Symposium Organizers
John F. Rabolt University of Delaware
Gregory C. Rutledge Massachusetts Institute of Technology
Bruce Chase DuPont Central Research
Joachim Wendorff Philipps University
WW1: Modeling and Theoretical Considerations in Polymer Nanofibers
Session Chairs
Tuesday PM, December 01, 2009
Room 203 (Hynes)
9:30 AM - WW1.1
Properties of Electrospinning Jets.
Darrell Reneker 1 , Tao Han 3 , Sureeporn Tripatanasuwan 1 , Alex Yarin 2
1 Polymer Science, University of Akron, Akron, Ohio, United States, 3 , Lanxess Corporation, Shanghai China, 2 , University of Illinois Chicago, Chicago, Illinois, United States
Show AbstractThe tensile stress in an electrospinning jet can be measured by creating a short lateral displacement pulse on a short segment of the jet, and observing the widening of the displaced region and the motion of the displacement pulse as it is carried by the jet [1]. These observations can be made even as the rheological properties of the fluid in the jet are changing because of evaporation of the solvent. The highest values of the tensile stress are found in the transitional region near the tip of the flow modified Taylor cone. The location along a tapering electrospinning jet at which the radial electric field is large enough to initiate a corona discharge in the surrounding air can be observed in real time with a highly sensitive video camera [2]. The value of the critical field for corona onset depends only slightly on parameters such as barometric pressure and relative humidity, but more directly on the diameter of the jet and the electrical charge density on the surface of the jet. Measurement of the diameter at which the corona occurs permits calculation of the charge per unit area on the surface. Charge is carried away from the jet by the air-borne ions in the corona, so the charge density carried downstream from the location at which the corona discharge stops is stabilized at the value at that point. These new observations, combined with other measurements, including the diameter of the jet as a function of position along the straight segment, velocity measurements as a function of position made with a laser Doppler velocimeter, flow rate of the fluid, electrical current, electrical conductivity and viscoelastic parameters of the fluid, enlarge our insight into the performance and control of electrospinning jets that produce nanofibers [3,4]. _____________________1. “Viscoelastic Electrospinning Jets: Initial Stresses and Elongation Rheometry”, Tao Han, Alexander Yarin, Darrell H Reneker, Polymer, Volume 49 (2008) Pages 1651-1658, DOI:10.1016/j.polymer.2008.01.0352. “Corona discharge from electrospinning jet of poly(ethylene oxide) solution”, Sureeporn Tripatanasuwan, Darrell H Reneker, Polymer, Volume 60 (2009) Pages 1835 – 1837.3. "Electrospinning Jets and Polymer Nanofibers”, Darrell H. Reneker and Alexander L. Yarin, Polymer, Volume 49, Issue 10 (2008) Pages 2387-2425, DOI:10.1016/j.polymer.2008.02.002. Feature Article4. "Electrospinning of Nanofibers from Polymer Solutions and Melts”, D.H. Reneker, A.L. Yarin, E. Zussman, H. XuAdvances in Applied Mechanics, Vol. 41 pp 43-195, 2006
9:45 AM - WW1.2
Microscale Structural Model of Alzheimer's Aβ(1-40) Amyloid Fibril.
Raffaella Paparcone 1 , Markus Buehler 1
1 , MIT, Cambridge, Massachusetts, United States
Show AbstractAmyloids play a crucial role in several common severe and neurodegenerative diseases such as Parkinson’s disease, Alzheimer’s disease and type II diabetes. Many different amino acid sequences can convert to amyloid configuration, showing universal features such as an elongated unbranched morphology and a core structure that consists of a set of beta-sheets oriented in parallel to the fibril axis, with their strands perpendicular to this axis. Recent progress in the application of solid-state NMR and in growing peptide elongated microcrystals has provided detailed structural and biochemical information and revealed that the molecules composing the fibrils feature a high degree of uniformity. The understanding of the structural and mechanistic basis of such properties has become of particular interest in the biological community. The physical models that explain such properties remain, however, elusive. This is partly due to the fact that structural models of microscale amyloid fibrils are unknown, preventing bottom-up studies to describe the link between their hierarchical structure and physical properties. Here we present an atomistic-based multi-scale analysis, used to predict the structure of Alzheimer’s Aβ(1-40) fibrils in different morphologies. We perform a systematic analysis of the structure of amyloid fibers of different lengths and, on the basis of geometrical and energetic considerations, we propose a structural model of amyloid fibers with lengths of hundreds of nanometers at atomistic resolution. Our model predicts the formation of twisted amyloid microfibers with a periodicity on the order of 100 nm, in close agreement with experimental results1, providing a direct link between the atomistic details of small fibers to the overall geometric properties of larger-scale structures. We report a detailed structural analysis of amyloid structural models and present a quantitative comparison with experimental results. Our results for the first time provide a direct link between the amino acid sequence and structural features on scales of hundreds of nanometers.
10:00 AM - WW1.3
Hierarchical Structure Controls Nanomechanical Properties of Vimentin Intermediate Filaments.
Zhao Qin 1 2 , Laurent Kreplak 3 , Markus Buehler 1 2 4
1 Laboratory for Atomistic and Molecular Mechanics, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Center for Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada, 4 Center for Computational Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractIntermediate filaments (IFs), in addition to microtubules and microfilaments, are one of the three major components of the cytoskeleton in eukaryotic cells, playing a vital role in mechanotransduction and in providing mechanical stability to cells. Despite the importance of IF mechanics for cell biology and cell mechanics, the structural basis for their mechanical properties remains unknown. This has prevented us from answering fundamental structure-function relationship questions related to the biomechanical role of intermediate filaments, which is crucial to link structure and function in the protein material’s biological context. Here we utilize a novel atomistic-level model of the human vimentin dimer and tetramer, which is obtained through a bottom-up approach based on structural optimization via molecular simulation. Our model is validated against key geometric parameters extracted from experiments, including fibril diameter, fibril packing and intermolecular spacing. We use these models to study their response to mechanical tensile stress. We describe a detailed analysis of the mechanical properties and associated deformation mechanisms, and discover that the hierarchical structure of IFs is crucial in defining its unique mechanical properties. We observe a transition from alpha-helices to beta-sheets with subsequent interdimer sliding, which has been inferred previously from experiment. By upscaling our results, we report for the first time, a quantitative comparison to experimental results of IF mechanics, showing good agreements. By identifying the links between structures and deformation mechanisms at distinct hierarchical levels, we show that the multi-scale structure of IFs is crucial for their characteristic mechanical properties, in particular their ability to undergo severe deformation of ≈300% strain without breaking. Our results enable a new paradigm in studying biological and mechanical properties of IFs from an atomistic perspective, and lay the foundation to understanding how properties of individual protein molecules can have profound effects at larger length-scales.
10:15 AM - WW1.4
Mechanical Instabilities of Compliant Polymer Nanofibers.
Xiangfa Wu 1
1 Mechanical Engineering and Applied Mechancis, North Dakota State University, Fargo, North Dakota, United States
Show AbstractRecent experiments have indicated the unique mechanical behaviors of polymer nanofibers (e.g. electrospun nanofibers), including the size effect in their modulus and strength and the surface instabilities observed in fabrication (e.g. wrinkling) and tension tests (e.g. rippling). This study provides a continuum mechanics approach to account for the rippling conditions of polymer nanofibers subjected to large axial tension. The material of the polymer nanofibers [polyacronitrile (PAN)] is modeled as hyperelastic solid based on the stress-strain diagram obtained in single-fiber tension tests. As a result, critical rippling parameters are determined, including the critical stretch, ripple wavelength, and critical fiber radius, below which the polymer nanofibers cannot exist due to the spontaneous rippling. The model predictions are compared with the experimental results in the literature. Application of the present model to other polymer nanofibers (e.g. hollow nanofibers) is further considered.
10:30 AM - **WW1.5
Confined Assembly of Block Copolymer/Nanoparticle Nanofibers: Triaxial Electrospinning and Coarse-Grained Molecular Dynamics Modeling.
Vibha Kalra 1 , Jung Lee 1 , Jay Park 1 , Yong Joo 1
1 Chemical & Biomolecular Engineering, Cornell University, Ithaca, New York, United States
Show AbstractThe importance of spatial location of nanoparticles in polymer nanocomposite materials has fueled interest in using block copolymers (BCP) as particle guiding scaffolds. Researchers have tailored the surface chemistry of functional nanoparticles (NPs) to prevent aggregates and selectively place them in desired BCP domains. However, self-attracting NPs such as magnetite, having numerous potential applications in electrical and biomedical fields, tend to aggregate and phase separate from BCP matrix due to strong magnetic dipole attractions. To control the distribution and location of magnetic nanoparticles in a polymer matrix, we have combined electrospinning and confined assembly of polystyrene-b-polyisoprene (PS-b-PI) block copolymer. First, various confined assemblies with cylinders, concentric lamellar rings, and coexistence of both cylinders and concentric rings have been obtained in electrospun block copolymer nanofibers. This confined assembly is then utilized as a template to guide the placement of functional nanoparticles such as magnetite selectively into the PI domain in self assembled nanofibers. For 10 wt% NPs, a transition of morphology is seen from concentric rings to a bicontinuous phase with NPs uniformly dispersed in the PI domain. To further investigate the effect of the interfacial interaction and frustration due to physically confined environment on the self assembly in electrospinning, triaxial configuration has been used where the middle layer with block copolymer is sandwiched by the innermost and outermost silica layers. Our results indicate that confined-assembly is significantly altered by the presence and interaction with both inner and outer silica layers. When nanoparticles are incorporated into PS-b-PI with PI cylinder morphology and placed as the middle layer, the PI phase with magnetite nanoparticles migrates next to the silica layers. The migration of PI phase to the silica layers has been observed for the mixture of PS and PS-b-PI with PS cylinder morphology as the middle layer. Finally, to further understand the effect of flow conditions on the nanoparticle location in block copolymers, we have performed coarse grained molecular dynamics simulations under planar elongational flow where spatially and temporally periodic boundary conditions devised by Kraynik and Reinelt have been implemented for unrestricted simulation times. Our results show that the peak concentration of both selective nanoparticles at the center of the preferred domain and non-selective nanoparticles at the domain interface becomes broader with increasing elongation rate, suggesting that elongational flow can be used as another parameter to control nanocomposite self assembly. Our results also reveal that the onset of flow induced transition from lamellar to disordered morphology is greatly influenced by particle-particle and particle polymer interactions.
11:00 AM - WW1:Modeling
BREAK
WW2: Methods of Processing of Polymer Nanofibers I
Session Chairs
Yong Joo
Stanislav Petrik
Tuesday PM, December 01, 2009
Room 203 (Hynes)
11:30 AM - **WW2.1
Coaxial Electrospinning - A Versatile Approach to Engineering Polymer Nanofibers.
Andrew Steckl 1 , Daewoo Han 1 , Nick Bedford 1
1 , University of Cincinnati, Cincinnati, Ohio, United States
Show AbstractElectrospinning utilizes a voltage to induce sufficient charges in a polymer solution to overcome the surface tension of the liquid and force a fluid jet to be ejected. The liquid jet undergoes simultaneous whipping and evaporation resulting in a polymer fiber. This relatively straightforward technique has produced micro-/nano-fibers from a large variety of polymers. Advantages of the electrospinning process include: (a) control of the fiber diameter from micro- to nano-meter dimensions; (b) production of very long fibers (cm-km); (c) control over the fiber compositions; (d) spatial alignment of multiple fibers; (e) formation of membranes with very high surface-to-volume ratio. In this paper a review of coaxial electrospinning is presented. Coaxial electrospinning greatly expands the capability of electrospinning by enabling the formation of core-sheath fibers in a single step. This is accomplished by feeding two separate polymer solutions through a coaxial nozzle which consists of a central tube surrounded by a concentric annular tube. This core-sheath concept is extremely versatile, as it can combine different properties from core and sheath materials into a single fiber. Compared to alternative methods for core-sheath fiber production, coaxial electrospinning provides a simple, one step and highly cost-effective process. It can utilize a large variety of materials and controllable stack thickness of core-sheath structured fibers, without the need for vacuum, elevated temperature treatment, plasma exposure or sophisticated chemistry. The requirements for successful coaxial electrospinning are first discussed, including viscoelastic properties, immiscibility and inter-diffusion, dielectric constants, evaporation rates, solution feeding ratio, etc. Then several examples of coaxial electrospun fibers for various applications are reviewed: tissue engineering, controlled drug delivery, superhydrophobic membranes, encapsulation of biopolymers or fluids, micro/nanofluidic devices, molecular sensors and textile applications. Finally, potential new areas of application such as the formation of self-cleaning and self-powered fibers by coaxial electrospinning are considered.
12:00 PM - WW2.2
Photocatalytic Self Cleaning Textile Fibers by Coaxial Electrospinning.
Nick Bedford 1 , Andrew Steckl 1
1 , University of Cincinnati, Cincinnati, Ohio, United States
Show AbstractChemical degradation and self-cleaning by hydrophilic semiconductor photocatalysts, such as anatase phase titania (TiO2), have a wide range of applications, including toxic chemical decomposition, protective/self-cleaning clothing, self-cleaning glass, and self-cleaning membranes. Of particular note, chemically protective and self-cleaning clothing have obvious health, environmental, and military applications. Studies have been performed on titania treated textile materials, such as cotton or wool like fibers. A major shortcoming of these treated textiles is the poor surface-to-volume ratio (SVR), limiting the overall photocatalytic activity. One method for increasing the SVR of a fibrous material is to use electrospinning. Electrospinning is a versatile technique for producing micro-/nano-fibers from a large variety of polymers. Electrospinning utilizes a high voltage power supply to extract a liquid jet from a nozzle which is fed polymer solution by a syringe pump. Electrospinning can produce non-woven fiber mats with exceptional SVRs and high porosity.In this study, photocatalytic self-cleaning textile fibers with high SVR are created via coaxial electrospinning. Cellulose acetate (CA) is used as the core phase which after a deacetylation step becomes cellulose. Cellulose, a biopolymer of consisting of β-1,4-glycosidic linked D-glucose units, is one of the most abundant naturally occurring materials and is commonly found in green plant cell walls and wood. A major source of cellulose is cotton, 95% of which consist of cellulose. A dispersion of TiO2 nanoparticles, with and without a low concentration of CA, is used as the sheath phase. The titania nanoparticles attach to the electrospun fiber in flight by adhesion to hydroxyl groups already present in the CA. A simple deacetylation step produces cellulose fibers. The coaxial electrospun fibers show self cleaning effects in indoor lighting conditions and outperform electrospun cellulose fibers surface loaded with TiO2. At ~90 mW/cm2, the coaxial photocatalytic fibers completely degrade blue dyes solutions within seven hours, while TiO2 surface loaded fibers only degrade ~80% of the blue dye and do not experience any further change. The durability/washability of the photocatalytic fibers was tested against three staining agents and the fibers were shown to maintain their self cleaning properties after multiple staining and washing steps. Due to their increased SVR, the photocatalytic activity observed in the fibers created by coaxial electrospinning is comparable to that of micron sized TiO2 modified fibers exposed to ultraviolet light.
12:15 PM - WW2.3
Control of the Location and Morphology of Metal and Metal Oxide Catalysts in Nanofibers via Coaxial Electrospinning.
Nate Hansen 1 , Yong Joo 1
1 Chemical Engineering, Cornell University, Ithaca, New York, United States
Show AbstractMonoaxial electrospinning has been used to produce silica and polyacrylonitrile (PAN) nanofibers containing nickel nanocrystals and TiO2 nanoparticles, respectively. TEM, XRD, and XPS studies show that both the formation of nickel nanoscrystals in silica nanofibers from thermal treatment of the nickel nitrate precursor and the direct inclusion of prefabricated TiO2 nanoparticles into PAN solution give rise to a uniform distribution of metal and metal oxide phases throughout the nanofiber. As a result, less than 10% of total nickel and TiO2 nanoparticles reside on the fiber surface. To increase the surface concentration and reduce the total consumption of nickel and TiO2, coaxial electrospinning has been implemented, where pure silica precursor or PAN solution and that with high loading of the nickel precursor or TiO2 nanoparticles are used as the core and shell layer, respectively. These fibers, both monoaxial and coaxial, are employed in catalytic applications, silica/nickel nanofibers in the alkaline hydrolysis of biomass and PAN/TiO2 nanofibers in photocatalytic experiments. The use of coaxial electrospinning has shown two major improvements over monoaxially elecrospun nanofibers: i) an increase in catalytic efficiency with the same overall catalyst loading and ii) the ability to electrospin solutions with higher loading of catalysts on the skin layer that were previously unable to be electrospun by using the pure core solution as the driving force for electrospinning.
12:30 PM - WW2.4
Controlling Nanofiber Alignment and Packing Density Through the Modulation of Residual Surface Charge on Nanofibers during Electrospinning.
Vasudha Chaurey 1 , Nathan Swami 1 , Po-Chieh Chiang 2 , Yi-Hsuan Su 2 , Chia-Fu Chou 2
1 Electrical & Computer Engineering, University of Virginia, Charlottesville, Virginia, United States, 2 Institute of Physics, Academia Sinica, Taipei Taiwan
Show AbstractPolymeric nanofibers of well-controlled alignment, chemistry and packing density are necessary for the construction of scaffolds with modulated pore sizes and volumes for eventual applications within controlled biomolecule release and tissue regeneration systems. Electrospinning has been the technique of choice over several decades since it can generate biocompatible and biodegradable nanofibers over relatively large areas and with a high throughput. Commonly investigated methods for the alignment of nanofibers during electrospinning include mechanical rotation methods using a mandrel set-up [1] or electrostatic methods through insulator gaps on a conducting collector plate [2]. Within both these methods, the residual charge on the polymeric nanofiber during electrospinning can be used to control electrostatic repulsion between the deposited polymer nanofibers and the incoming polymer jet to enable a greater degree of control over nanofiber alignment and packing density. Prior studies have not systematically explored this methodology for nanofiber alignment. In this work the residual surface charge on electrospun polymeric nanofiber was varied by two methods – varying the “grounded” area on the collector plate where the polymer charge may be neutralized and through the use of polymers with differing charged side-groups. Polymers such as PLAGA (Poly-Lactic Gycolic Acid), PCL (polycaprolactone) and blended polymers were used to study the effects of residual nanofiber charge on alignment. The degree of alignment of the resulting nanofibers was characterized using Fourier transform image processing methods [3]. The alignment of fibroblast cells on these nanofiber scaffolds for varying degrees of alignment and packing was characterized to correlate the direction of nanofiber alignment to that of the differentiated cell alignment for various configurations of residual nanofiber charge during electrospinning. Based on these results we present a possible methodology for the control of nanofiber alignment and packing density through the control of residual surface charge on the polymeric nanofiber during electrospinning [4].References[1] Corey, J.M., Lin, D.Y., Mycek,K. B., Chen, Q., Samuel, S., Feldman, E, Martin, D.C. “ Aligned electrospun nanofibers specify the direction of dorsal root ganglia neurite growth”, Journal of Biomedical Materials Research Part A DOI 10.1002 (2007).[2] Li D, Wang YL, Xia YN, “Electrospinning nanofibers as uniaxially aligned arrays and layer-by-layer stacked films”, Advanced Materials, 16, 361-366, (2004).[3] Ayres CE, Jha BS, Meredith H, Bowman JR, Bowlin GL, Henderson SC, Simpson DG, “Measuring fiber alignment in electrospun scaffolds: a user's guide to the 2D fast Fourier transform approach” J. Biomater. Sci. Polymer Edn, Vol. 19, No. 5, pp. 603–621 (2008).[5] V. Chaurey et al, “Control of nanofiber alignment through the modulation of surface charge” (Manuscript in preparation).
12:45 PM - WW2.5
Fabrication of Highly Conductive Pedot Nanofibers.
Alexis Laforgue 1 , Lucie Robitaille 1
1 Industrial Materials Institute, National Research Council Canada, Boucherville, Quebec, Canada
Show AbstractThe development of polymer nanofibers represents a research area of great interest due to the variety of potential applications. Electrospinning is one of the most promising techniques for the production of nanofibers thanks to its versatility and relative simplicity. In the past few years, an increasing number of studies has been dedicated to the fabrication of electrospun nanofibers containing intrinsically conductive polymers (ICPs) such as polyaniline, polypyrrole, polythiophenes, poly(p-phenylene vinylenes) or polyfluorenes. Potential applications of such nanofibers include conductive textiles, flexible organic electronics, energy storage and sensors. Poly(3,4-ethylenedioxythiophene) (PEDOT) is one of the most conductive and stable ICP. In 2004, Winther-Jensen et al. reported the preparation of PEDOT ultrathin films showing conductivities exceeding 10E3 S/cm using a vapour-phase polymerization process [1]. However, much lower conductivities, in the order of 10E4 - 1 S/cm, have been reported for electrospun fibers incorporating PEDOT [2,3]. Conductivities in the order of 10 S/cm were also observed on PEDOT nanofiber webs but the fiber geometry was not preserved and the webs were transformed into a porous film structure upon rinsing procedures [4].A two-step process to obtain pure PEDOT nanofibers was developed by using a combination of electrospinning and vapour-phase polymerization [5]. The first results led to highly conductive porous materials (200 S/cm) but the fibers partially “melted” in the process.In this paper, we will describe the optimization of the technique, that allowed the fabrication of well defined nanofibers of pure PEDOT. The average fiber diameter was 350 ± 50 nm. The conductivity of the fiber mats was measured to be around 60 ± 10 S/cm. The paper will present a complete structural and morphological study as well as spectroscopic and electrochemical characterizations of the nanofiber mats. The integration of the PEDOT nanofiber mats into flexible energy storage devices will be also presented.[1] B. Winther-Jensen, J. Chen, K. West, G. Wallace, Macromolecules 2004, 37, 4538.[2] A. El-Aufy, B. Naber, F.K. Ko, Polymer Preprints 2003, 44, 134.[3] S. Nair, E. Hsiao, S.H. Kim, Chem. Mater. 2009, 21, 155.[4] H.D. Nguyen, J.M. Ko, H.J. Kim, S.K. Kim, S.H. Cho, J.D. Nam, J.Y. Lee, J. Nanosci. Nanotech. 2008, 8, 4718.[5] A. Laforgue, L. Robitaille, Polym. Preprint 2008, 49(2), 624.
WW3: Methods of Processing of Polymer Nanofibers II
Session Chairs
H. Young Chung
Andrew Steckl
Tuesday PM, December 01, 2009
Room 203 (Hynes)
2:30 PM - WW3.1
Controlling the Crystalline State of Electrospun Nylon 6 by Varying the Solvent Evaporation Kinetics.
Carl Giller 1 , Bruce Chase 1 , John Rabolt 1 , Christopher Snively 1
1 Materials Science and Engineering, University of Delaware, Newark, Delaware, United States
Show AbstractThe role of solvent evaporation on the crystalline state of electrospun Nylon 6 fibers was examined by electrospinning into a closed chamber filled with varying concentrations of solvent vapor. Previous studies have established that electrospun Nylon 6 fibers exhibit the γ form crystalline polymorph. In this study, it was found that the thermodynamically stable α form became increasingly present in Nylon 6 fibers electrospun out of both 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) and formic acid as the vapor phase solvent concentration increased. It is believed that the formation of the metastable γ form is due to the fast solvent evaporation kinetics associated with the electrospinning process. By varying the rate of solvent evaporation during electrospinning, we were able to control the resulting crystal structure of the electrospun Nylon 6, as evidenced by XRD and Raman and FTIR spectroscopies. We are currently examining whether this behavior is universally observed across all families of polymorphic polymers.
2:45 PM - WW3.2
Electric-Field-Induced Polyethylene Nanofibrils with Highly Oriented Crystalline Structure by Solvent Evaporation-Controlled Electrospinning.
Taiyo Yoshioka 1 , Roland Dersch 2 , Masaki Tsuji 3 , Andreas Schaper 1
1 Material Sciences Center, Philipps University, Marburg Germany, 2 Department of Chemistry, Philipps University, Marburg Germany, 3 Institute for Chemical Research, Kyoto University, Uji Japan
Show AbstractThe development of a method to fabricate polymer nanowires with a diameter of several tenth nanometers or less is desired in various fields, such as nanowire transistors, solar cells, photo-detectors, and bio-sensors. We developed a fabrication technique of polymer nanowires with very thin diameter, narrow size distribution, and highly developed fiber structure, by a special electrospinning technique. In this study, we have performed experiments on high temperature electrospinning of polyethylene (PE) solutions. In order to induce a strong elongational force to the electrospun fibers a collecting system composed of a pair of parallel conductive stripes with an insulating gap (termed as “parallel electrode collector”) for collecting the fibers in parallel fashion was used. The collecting system creates a split-electric-field just above the collector. Under those conditions, fibers having a multiple-fibrillated structure composed of fibrillated and non-fibrillated parts were produced, when the fibers arrived at the split-electric-field before solidification. The fibrillated parts are composed of many thin fibrils with a narrow diameter distribution of 10-30 nm. The selected-area electron diffraction (SAED) analysis showed that each fibril is composed of a highly oriented crystalline structure while the non-fibrillated parts are almost unoriented. The formation mechanism of the highly developed fiber structure in the fibrils will be discussed. It is suggested that this special electrospinning method can be applied to various polymer systems as a method to fabricate extremely thin and uniform nanowires.
3:00 PM - WW3.3
Synthesis of Porous Nanofibers from Metal Organic Frameworks.
Laura McJilton 1 , Hiroyasu Furukawa 2 , Aaron Strickland 1 3 , Juan Hinestroza 1 3
1 , Cornell , Ithaca, New York, United States, 2 , UCLA, LA, California, United States, 3 , iFyber, LLC, Ithaca, New York, United States
Show AbstractSynthesis of porous nanofibers that trap selected gasses allow for a variety of applications, including filtration and sequestering of gas. Metal Organic Polyhedra (MOPs) and Metal Organic Frameworks (MOFs) nodes of metal ions or carboxylate clusters joined by organic links, have attracted attention due to their ability to capture and retain gases [1]. Recent work has led to the formation of discrete nanoparticles of MOPs and MOF material soluble in organic solvents [2-3]. These innovations suggest formation of a composite textile material for gas storage and filtration applications composed of MOFs and MOPs embedded in textile fibers. In order to form flexible textiles for filtration, MOPs and MOFs are incorporated into nylon nanofibers by direct mixing and in situ synthesis on the nanofiber surface.[1] Design, synthesis, structure, and gas (N2, Ar, CO2, CH4 and H2) sorption properties of porous metal-organic tetrahedral and heterocuboidal polyhedra, A. Sudik, N. Ockwig, A. Millward, A. P. Côté, O. M. Yaghi, J. Am. Chem. Soc., 2005, 127, 7110.[2] Crystal Structure, Dissolution, and Deposition of a 5 nm Functionalized Metal-Organic Great Rhombicuboctahedron, H. Furukawa, J. Kim, K. E. Plass, and O. M. Yaghi, J. Am. Chem. Soc., 2006, 128, 8398-8399.[3] Assembly of Metal−Organic Frameworks from Large Organic and Inorganic Secondary Building Units: New Examples and Simplifying Principles for Complex Structures, j. Kim, B. Chen, T. Reineke, H. Li, M. Eddaoudi, D. Moler, M. O’Keeffe, O. M. Yagi, J Am. Chem. Soc., 2001, 123, 8239
3:15 PM - WW3.4
Phase Transitions of Liquid Crystals Confined Inside Carbon Nanopipes: A Modulated DSC Study.
Nihar Pradhan 1
1 Physics, Worcester Polytechnic Institute, Worcester, Massachusetts, United States
Show AbstractAbstract:Liquid crystalline materials confined to restrictive nano-channels are of great interest in recent years because of their potential application in electro-optics and display technology. This calorimetric and imaging study focuses on thin, 30 ~ 40 nm thick, films of 8CB and 10CB liquid crystals coating the inner walls of hollow aligned Multi-Wall Carbon Nanopipes (MWCNPs). The MWCNPs were grown inside ~200 nm diameter Anodic Aluminum Oxide (AAO) nano-channels. A TEM study confirmed the film coating of the inner surfaces of MWCNPs by the liquid crystals and characterized their geometry. The phase transition characteristics of the confined liquid crystal films were studied using a modulated DSC technique. Here, the isotropic to smectic-A (10CB), the isotropic to nematic (8CB), and the nematic to smectic-A (8CB) were studied in the aligned MWCNP within the AAO nano-channels and in liberated MWCNP in a random packed sample. The unique shifting of phase transition temperatures, change of amplitude and broadening of the heat capacity peaks from the bulk samples will be presented.
3:30 PM - WW3.5
Significant Increase in Electrical Conductivity of Electrospun MEH-PPV/PEO/LiCF3SO3 Submicron Fibers by Post-stretching.
Yuya Ishii 1 , Heisuke Sakai 1 , Hideyuki Murata 1
1 School of Materials Science, Japan Advanced Institute of Science and Technology, Nomi shi, Ishikawa ken, Japan
Show AbstractUniaxial alignment of conjugated polymer is intensively studied because of their unique properties, such as enhanced conductivity, polarized luminescence and absorption, and in-plane refractive index anisotropy. We have succeeded to produce uniaxially aligned single submicron conjugated polymer fiber by a newly developed electrospinning method, which allows us to precisely control the number and alignment of submicron fibers. In this presentation, we focus on electrical conductivity of electrospun single fiber as a function of stretching ratio. Unstretched electrospun poly[2-methoxy-5-(2’-ethyl-hexyloxy)-1, 4-phenylenevinylene] (MEH-PPV)/ poly(ethylene oxide) (PEO)/LiCF3SO3 single fiber shows 3.0 times higher electrical conductivity than that of the spin-coat film of MEH-PPV/PEO/LiCF3SO3. The electrical conductivity is further improved as a function of stretching ratio. After the stretching of the MEH-PPV/PEO/LiCF3SO3 submicron fibers up to 1.5 times and 2.0 times, the electrical conductivity of the MEH-PPV/PEO/LiCF3SO3 submicron fibers increase in 12.7 times and 127 times compared with that of the unstretched fiber. Polarized photoluminescence studies suggest that enhancement in electrical conductivity is ascribed to the chain alignment of MEH-PPV in the submicron fibers. References1) Y. Ishii, H. Sakai, and H. Murata, Mater. Lett. 62, 3370 (2008). 2) M. Campoy-Quiles, Y. Ishii, H. Sakai, and H. Murata, Appl. Phys. Lett. 92, 213305 (2008).
3:45 PM - WW3.6
Nylon Nanofibers Mat Effectively Reinforcing Polyaniline Thin Films.
Angel Romo-Uribe 1 , Layza Arizmendi 2 , Maria Romero-Guzman 1 , Selene Sepulveda-Guzman 3 , Rodolfo Cruz-Silva 4
1 Instituto de Ciencias Físicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, Mexico, 2 Polimeros, Centro de Investigación en Ingeniería y Quimica Aplicada, Saltillo, Coahuila, Mexico, 3 Centro de Innovación, Investigación y Desarrollo en Ingeniería y Tecnología, Universidad Autónoma de Nuevo León, Monterrey, Nuevo Leon, Mexico, 4 Centro de Investigación en Ingeniería y Ciencias Aplicadas, Universidad Autónoma del Estado de Morelos, Cuernavaca, Morelos, Mexico
Show AbstractThis research demonstrates that nylon nanofiber (NNF) mat can be an effective mechanical reinforcement to polyaniline (PANI) thin films. Nanofibers of ca. 250 nm diameter were produced by electrospinning of a nylon 6 solution in formic acid. Scanning electron microscopy (SEM) showed that the solution impregnation method utilized was effective to embed the nanofibers into the PANI matrix. The effectiveness of nylon nanofibers as mechanical reinforcement of a PANI thin film was assessed via dynamic mechanical analysis in tension mode. The as-cast PANI films displayed a tensile dynamic modulus, E’, of ca. 0.65 GPa at room temperature. Scanning in temperature showed that the PANI film has a usage temperature of up to about 80°C, this being limited by its glass transition temperature, and over this temperature range the elastic modulus was nearly independent of temperature. On the other hand, the PANI-nanofiber composite displayed a significantly higher tensile modulus at room temperature (1.1 GPa) and its usage temperature was extended up to just over 200°C, this being limited by the melting transition of nylon 6 (at 220°C). The results therefore showed that the NNF mat increased the usage temperature of PANI films over 100°C opening up applications for PANI membranes.
4:00 PM - WW3: Proc II
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4:30 PM - **WW3.7
Production Nozzle-Less Electrospinning Nanofiber Technology.
Stanislav Petrik 1
1 , ELMARCO s.r.o., Liberec 9 Czechia
Show AbstractTheoretical background and technical realization of the free liquid surface (nozzle-less) electrospinnig process will be described. The process is the basis of both laboratory and industrial production machines called NanospiderTM. Technical capabilities of the machines (productivity, nanofiber layer metrics, and quality consistency) will be described in detail. Comparison with competing/complementary technologies will be given, e.g. nozzle electrospinning, nano-meltblown, islets-in-the sea, centrifuge, etc. Application fields for nanofiber materials produced by various methods will be discussed.An overview of the applications for electrospun nanofibers will be presented:- Composite nanofiber materials for final products used in biomedical applications (wound care, surgery), sound absorption, filtration, and their recent test results- Newest achievements in development of unique materials for energy generation and storage (batteries, supercapacitors, fuel cells, and solar cells), catalysts, and composite materials
5:00 PM - WW3.8
Fabrication of Well-aligned 3D Nanofibrous Scaffold through Rotary Spinning System.
Mohammad Badrossamay 1 , Josue Goss 1 , Kevin Parker 1
1 School of engineering & Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Show AbstractA three-dimensional (3D), highly porous substrate can mimic in vivo cell-matrix interactions more accurately than more commonly used two-dimensional substrates [1]. Nanofiber structures have been widely employed as scaffolds in tissue engineering due to their high surface to mass ratios, high porosities, simple fabrication and geometric versatility [1-5]. Electrospinning (ES) is currently the most common technique used for nanofiber formation [1-6]. However, ES has several drawbacks, including high-voltage electrical field requirements, aligned fiber set up constraints, low production rates, and 3D fabrication restrictions [6]. Therefore, it is necessary to explore new, more reliable methods to generate aligned micro- and nano-scale polymeric fibers. We have developed a facile and effective method for fabricating well-aligned 3D fiber structures by using a rotary spinning system (RSS). The polymer used in this report was poly (lactic acid), though other synthetic or naturally occurring polymers may be used. Solution of 8wt% PLA in chloroform was continuously fed to the rotating reservoir and the resulting fibers were collected on a round collector. Continuous, well-aligned PLA fibers with diameters ranging from 50-3500nm can be achieved from PLA solution. The morphology and pore configuration of the nanofibers could be tailored easily by altering the solution properties and rotation speed of the rotor. In compare to other nanofiber fabrication methods, RSS does not require a high-voltage electrical field, but is instead driven by centrifugal forces. Nanofiber fabrication is independent of solution conductivity. The resulting nanofibers can be fabricated into 3D structures of any arbitrary shape by varying the collector geometry. We believe that uniaxially aligned fiber structures formed by RSS can be used in a variety of bioengineering applications, such as cardiac, neural or vascular tissue engineering. Additionally, the 3D aligned fiber structures can be used in electronic and photonic devices and polymer composites. References:1-J Xie, et. al. Macro. Rap. Com. 29 (2008), 1775.2-D Lia, YN Xia, Adv. Mater. 16 (2004), 1151.3-WE Teo and S Ramakrishna, Nanotechnology 17 (2006) R89.4-CA Bashura, et. al. Biomaterials 27 (2006) 5681.5-PA Madurantakam , et. al , Nanomedicine 4 (2009), 193.6-RT Weitz, et. al . Nano Letters 8 (2008), 1187.
5:15 PM - WW3.9
Tunable Helical Cylinder Nanofibers via Kinetic Assembly of Charged Block Copolymer in Solution.
Sheng Zhong 1 , Ke Zhang 2 , Karen Wooley 2 , Darrin Pochan 1
1 Department of Materials Science and Engineering and Delaware Biotechnology Institute, University of Delaware, Newark, Delaware, United States, 2 Center for Materials Innovation, Department of Chemistry and Department of Radiology, Washington University in Saint Louis, Saint Louis, Missouri, United States
Show AbstractA multi-micrometer-long, helical cylinder is produced from kinetic coassembly of poly(acrylic acid)-block-poly(methyl acrylate)-block-polystyrene (PAA-b-PMA-b-PS) triblock copolymers with excess triethylenetetramine or diethylenetriamine, in a mixture of 67% volume ratio of water in tetrahydrofuran (THF). Both single- and double-stranded helices and left- and right-handed helix are found in the same system. Cryogenic transmission electron microscopic study shows that the kinetic pathway for formation of helical cylinders undergoes a complex but reproducible, nanostructure evolution which involves the long-range stacking of bended cylinders at early stages and the subsequent interconnection of these bended cylinders. Spherical micelles bud off of the interconnected nanostructure as the final step towards a defect-free helix. This transition occurs at stable temperature and solution composition and is due to the redistribution of excess amine molecules around hydrophilic corona. The stable pitch distance of the formed helices, which is due to unevenly distributed amine molecules in the micellar corona, can be efficiently tuned by varying the type and amount of the multivalent amine molecules, adding monovalent salt as well as tuning the pH of the solution.
5:30 PM - WW3.10
Electrospun Nanoparticle-Nanofiber Composites via a Novel One-Step Synthesis.
Carl Saquing 1 , Joshua Manasco 1 , Christina Tang 1 , Saad Khan 1
1 , North Carolina State University, Raleigh, North Carolina, United States
Show AbstractWe examine a facile approach to synthesize and incorporate metal nanoparticles (NPs) into electrospun polymer nanofibers (NFs) wherein the electrospinning polymer acts as both a reducing agent for the metal salt precursor, as well as a protecting and templating agent for the ensuing nanoparticles (Saquing et al., Small 2009). Such a true one-step process at ambient condition that is free of organic solvents is demonstrated using two systems: one comprised of poly(ethylene oxide) (PEO), at electrospinnable molecular weights of 600, 1000 or 2000 kDa, and the other involving alginate-polyethylene oxide blends, both containing AgNO3 salt. The PEO or the alginate transforms Ag+ ions to Ag NPs, a phenomenon which has not been previously possible without the addition of a separate reducing agent and stabilizer or the application of heat. Results from x-ray photoelectron spectroscopy and ultraviolet and visible absorption spectrophotometry analyses support the formation of pseudo-crown ethers in high MW PEO as the mechanism in the development of NPs. The Ag NPs reduce fiber diameter and enhance fiber quality (reduced beading) due to increased electrical conductivity. Interestingly, several of the nanofibers exhibit Ag NP localized nanochain formation and protrusion from the nanofiber surface that was found to be attributed to the combined effect of applied electrical field on the polymer and the differences between the electrical conductivity and polarizability of the polymer and metal NPs. Furthermore, we also present our investigation of the effect of adding a surfactant in facilitating the electrospinning of NP-loaded alginate-PEO solution. Results show that both the alginate to PEO and NP to polymer ratios can be increased significantly with the addition of micellar concentrations of surfactant to generate bead-free nanofibers. Viscosity scaling relationships of the alginate-PEO-AgNO3-surfactant aqueous system were also obtained to determine the role of chain entanglement and its correlation to solution properties (including surface tension and electrical conductivity) in fiber formation during electrospinning.
5:45 PM - WW3.11
Study of the Growth of PANI Nanofibers by Various Methods and its Effect on Hydrogen Storage.
Rudran Retnadurai 1 , Michael Niemann 1 , Sesha Srinivasan 1 , Ayala Phani 2 , Yogi Goswami 1 , Elias Stefanakos 1 , Ashok Kumar 1
1 Clean Energy Research Center, University of South Florida, Tampa, Florida, United States, 2 , Nano-RAM Technologies, Bangalore India
Show AbstractSyntheses of Polyaniline (PANI) nanofibers have been carried out using the chemical method by varying the time and temperature of nucleation. The polymers’ growth characteristics and surface morphologies were analyzed. It has been found that the formation of nanofibers vary with the nucleating temperature and cross linking time. Growth of dendritic structures and fiber sprouts suggest that the growth kinetics depend very much on the mechanical agitation of the polymer solution during synthesis. PANI nanofibers (NF) with rough surfaces are found to be formed when synthesized with constant agitation at 5°C. On the other hand, smooth PANI NF were formed when synthesized with constant agitation at about 0°C. PANI blooms with fiber sprouts reveal an insight on the actual growth of these nanofibers. It has not been clearly mentioned in literature so far if the surface morphology of PANI nanofibers plays a role in the hydrogen storage. Therefore, in the current investigation, extensive hydrogen adsorption/desorption (PCT) studies have been carried out on the various synthesized PANI nanofibers.
Symposium Organizers
John F. Rabolt University of Delaware
Gregory C. Rutledge Massachusetts Institute of Technology
Bruce Chase DuPont Central Research
Joachim Wendorff Philipps University
WW4: Characterization of Structure and Morphology of Polymer Nanofibers
Session Chairs
Dawnielle Farrar
Eyal Zussman
Wednesday AM, December 02, 2009
Room 203 (Hynes)
9:45 AM - WW4.1
Molecular Characterization of Orientation and Order in Electrospun Polymer Nanofibers.
John Rabolt 1
1 Materials Science and Engineering, University of Delaware, Newark, Delaware, United States
Show AbstractAlthough electrospun polymer nanofibers have been the subject of extensive study over the last decade, the ability to align polymer chains relative to the macroscopic fiber axis has not been well understood. In order to enhance the mechanical and, perhaps, the electrical and optical properties of these fibers, orientation of the polymer backbones along the direction of the fiber axis must be achieved. Using a combination of electric field induced fiber collection/alignment and a series of semicrystalline polymers and biopolymers, we have been able to produce macroscopically aligned fiber sheets with very high molecular orientation of polymer chains parallel to the fiber axis. Electron microscopy, Raman spectroscopy, infrared spectroscopy and wide angle x-ray diffraction have been used to characterize and quantify the extent of orientation of the polymer backbones in polymeric fibers with diameters in the range of 200-2000 nm. In addition, “real-time” studies of polymer solutions using polarized Raman spectroscopy have revealed that molecular orientation does exist as the polymer passes through the stable part of the electrospun jet. Methods to “freeze in” this orientation will be discussed. Recently we have perfected (1) the technique of AFM probe electrospinning and applied it to the production of polymer nanofibers. The enhanced electric field strength and reduced working distance afforded by this new technique combine to produce polymer nanofibers with reduced crystalline content, perhaps due to a “quenching” affect.1. S. Sullivan, T. Beebe and J. Rabolt, private communication (
10:00 AM - WW4.2
Molecular Orientation Evolution During Electrospinning Of Atactic Polystyrene Using Real-Time Raman Spectroscopy.
Giriprasath Gururajan 1 , Carl Giller 1 , Christopher Snively 1 , Bruce Chase 1 , John Rabolt 1
1 Dept. of Materials Science and Engg., University of Delaware, Newark, Delaware, United States
Show AbstractReal-time Raman spectroscopy was successfully utilized to monitor solvent evaporation and molecular orientation during electrospinning of atactic polystyrene (a-PS). The importance of jet stability for real-time measurements has been reported in our previous study. Therefore, a binary solvent system of N, N-dimethyl formamide (DMF) and tetrahydrofuran (THF) was used with a-PS in this study, which insured a stable straight jet during the experiment. The strong Raman bands centered at 866 cm-1, 914 cm-1 and 1004 cm-1 unique to DMF, THF and a-PS respectively, were used to monitor concentration changes for different processing parameters: concentration, flow-rate and electric-field strength. The changes in the intensity of a radial skeletal ring vibration of the aromatic group at 623 cm-1 in two different polarization geometries: ZZ and YY were monitored for orientation measurements. This study reports the first of a kind quantitative vibrational spectroscopic measurement during the electrospinning process. A significant change in concentration and orientation was observed during the process. The changes are explained in relation to the process.
10:15 AM - WW4.3
Effects of One-dimensional Confinement on Polymer Morphology: Characterization of Sub-micron Thermoplastic Fibers Prepared Using Islands-in-the-sea Approach.
Elizabeth Welsh 1 , Michael Sennett 1 , Peter Stenhouse 1
1 , US Army Natick Soldier Research, Development & Engineering Center, Natick, Massachusetts, United States
Show AbstractConfinement of a polymer in one or more dimensions at sub-micron length scales can have significant and unpredictable effects on polymer structure and properties. Understanding these effects in nanofiber geometry has the potential to improve control of fiber properties. This may allow for the creation of fibers with specific properties optimized for particular applications, enhance the level of performance of fibers in existing applications or create new applications for nanofibers. This in turn could lead to more effective textiles and composites for ballistic protection, improved microfiber or nanofiber strength for improved textile durability, and utilization of small diameter fibers to impart permselectivity, sensing, and decontamination functionalities into textiles. Critical confinement dimensions vary depending on the polymer or system being studied, but range from about 1 micron to 10’s of nanometers. The nanofiber diameter can also be influenced by confinement geometry and interfacial effects of the polymers. Multi-component islands-in-the-sea fiber melt-spinning techniques have been used to create sub-micron nanofibers (the islands) in a confining matrix (the sea) at high rates. Bicomponent fiber trials were conducted using a high island count to produce fibers with up to 120,000 islands-in-the-sea. Trials using polypropylene as the nanofibers with poly(lactic acid) or polyethylene as the confining polymer were fabricated. The nanofiber confinement diameter was controlled by varying the number and volume fraction of the islands as well as processing conditions. Preliminary results indicate that the amount of orientation occurring within the nanofibers varies depending on processing conditions. Initial investigation indicates nanofiber diameter size in the 100 nanometer range and below. The relationship between polymer morphology and properties will be reported including crystallite size within the nanofibers, degree of confinement and quasi-static and dynamic mechanical properties. The results of WAXD analysis, AFM analysis, thermal analysis, and microscopy will also be reported.
10:30 AM - WW4.4
Crystal Polymorphism in Electrospun Composite Nanofibers of Poly(vinylidene fluoride) with Nanoclay.
Lei Yu 1 , Peggy Cebe 1
1 Physics, Tufts University, Medford, Massachusetts, United States
Show AbstractWe investigated for the first time the morphology and crystal polymorphism of electrospun composite nanofibers of poly(vinylidene fluoride) (PVDF) with two nanoclays: LucentiteTM STN and SWN. Both nanoclays are based on the hectorite structure, but STN has organic modifier in between the layers of hectorite while SWN does not. PVDF/nanoclay was dissolved in N,N-dimethylformamide/acetone and electrospun into composite nanofiber mats with fiber diameters ranging from 50~800 nm. Scanning electron microscopy shows that addition of STN and SWN can greatly decrease the number of beads and make the diameter of the nanofibers more uniform due to the increase of electrospinning solution conductivity brought by the nanoclay. Infrared spectroscopy and X-ray diffraction confirm that both STN and SWN can induce more extended PVDF chain conformers, found in beta and gamma phase, while reducing the alpha phase conformers in electrospun PVDF/Nanoclay composite nanofibers. With the attached organic modifier, even a small amount of STN can totally eliminate the non-polar alpha crystal conformers. The ionic organic modifier makes STN much more effective than SWN in causing crystallization of the polar beta and gamma phases of PVDF. An ion-dipole interaction mechanism is utilized to explain the crystal polymorphism behavior in electrospun PVDF/nanoclay composite nanofibers.
10:45 AM - WW4.5
Fabrication and Characterization of High Aspect Ratio Conducting Polymer Fibers.
Miguel Saez 1 , Lauren Montemayor 2 , Priam Pillai 1 , Ian Hunter 1
1 BioInstrumentation Laboratory, Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractElectroactive conducting polymers are currently studied for use in smart textiles that incorporate sensing, actuation, control, and data transmission. The development of intelligent garments that integrate these various functionalities over wide areas (i.e. the human body) requires the production of long, highly conductive, and mechanically robust fibers. This study focuses on the electrical, mechanical and electrochemical characterization of high aspect ratio polypyrrole fibers produced using a novel, custom-built fiber slicing instrument. In order to ensure high conductivity and mechanical robustness, the fibers are sliced from tetra-ethylammonium hexafluorophosphate-doped polypyrrole thin films electrodeposited onto a glassy carbon crucible. The computer-controlled, four-axis slicing instrument precisely cuts the film into thin, long fibers by running a sharp blade over the crucible in a continuous helical pattern. This versatile fabrication process has been used to produce free-standing fibers with square cross-sections of 2 μm × 3 μm, 20 μm × 20 μm, and 100 μm × 20 μm with lengths of 15 mm, 460 mm, and 1,200 mm, respectively. An electrochemical dynamic mechanical analyzer built in-house for nano- and microfiber testing was used to perform stress-strain and conductivity measurements in air. The fibers were found to, on average, have an elastic modulus of 1.7 GPa, yield strength of 37 MPa, ultimate tensile strength of 80 MPa, elongation at break of 49%, and an electrical conductivity of 12,700 S/m. SEM micrographs show that the fibers are free of defects and have cleanly cut edges. Preliminary measurements of the fibers’ strain-resistance relationship have resulted in gage factors suitable for strain sensing applications. Initial tests of the actuation performance of fibers in neat 1-butyl-3-methylimidazolium hexaflourophosphate have shown promising results. These monofilament fibers may be spun into yarns or braided into 2- and 3-dimensional structures for use as actuators, sensors, antennae, and electrical interconnects in smart fabrics.
11:00 AM - WW4: Structure
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11:30 AM - **WW4.6
Electrospinning of Nanofibers - A Morphological Study.
Eyal Zussman 1
1 Mechanical Engineering, Technion, Haifa Israel
Show AbstractIn the electrospinning process, a polymer solution is extruded from a spinneret, and in the presence of a sufficiently strong electric field, a jet is formed at the tip. This jet then undergoes extreme elongation thereby stretching the polymer molecules within it. As this is occurring, the rapid solvent evaporation fixes the polymer matrix in this stretched, yet non-equilibrium state. This process allows for the fabrication in a single stage and in less than 10 ms, of nanofibers. The morphology and mechanical properties of the collected fibers are commonly studied by focusing on the parameters of the electrospinning process. However, the effect of the evaporation rate on the physical features of the electrospun fibers has not been studied in detail. The very rapid evaporation process is a challenging problem for experimental investigation. In particular, it was demonstrated that when the evaporation is very fast, the polymer density at the fiber/vapor interface increases sharply, thus creating a polymer density gradient that acts as a barrier, or skin, that resists further solvent evaporation. These results are in good agreement with our presumption that despite the rapid evaporation that has occurred, the collected electrospun nanofibers still contain a significant amount of solvent. The presence of the solvent, which now evaporates even slower due to the barrier that has formed, apparently results in “relaxation” of the fabricated nanofibers. This relaxation causes certain post-processes to take place within the system, e.g. buckling of core-shell fibers which will discussed in the lecture.
12:00 PM - WW4.7
Morphology and Internal Structure of Electrospun Poly(vinylidene difluoride) and Poly(vinylidene fluoride-co-trifluroethylene) nanofibers
Zhenxin Zhong 1 , Darrell Reneker 1
1 Polymer Science, University of Akron, Akron, Ohio, United States
Show AbstractPoly(vinylidene fluoride) (PVDF) and its trifluoroethylene copolymers (PVDF-TrFE) have drawn great attention due to their attractive electrical properties including ferro-, piezo- and pyro-electricity. Electrospun nanofibers provide a unique morphology to study the crystallization behaviors of the polymers at the nanoscale. The morphology, polymorphic behavior and internal structure of electrospun PVDF and PVDF-TrFE nanofibers were investigated by atomic force microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, differential scanning calorimety and FT-IR spectroscopy. The effect of annealing on the structure of electrospun nanofiber was also studied. Long cylindrical specimens with cross-sections in the range of 10 nm to several micons were obtained by electrospinning. PVDF fibers electrospun from acetone solution are porous and contain both alpha and beta phase crystals. Almost pure beta phase was obtained in electrospun PVDF nanofibers from dimethyl sulfoxide solution. The electron diffraction diagrams reveal the polymer molecules were aligned with the fiber axis. Low dose electron diffraction of fibers annealed at 130 oC showed a higher fraction of the molecular chains aligned with the fiber axis than in the as spun fiber. For an electrospun PVDF-TrFE fiber annealed above its Curie point, the rearrangement of polymer molecules leads to the formation of ordered nanoscale patterns in the fibers. Morphological changes induced by intense electron irradiation in electrospun nanofibers were characterized.
12:15 PM - WW4.8
Wrinkled Surface Topographies and Internal Porous Morphologies of Electrospun Polymer Fibers.
Chia-Ling Pai 1 , Lifeng Wang 2 , Mary Boyce 2 , Gregory Rutledge 1
1 Chemical Engineering, MIT, Cambridge, Massachusetts, United States, 2 Mechanical Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractA variety of irregular cross-sectional shapes and corresponding wrinkled surface textures have been observed in electrospun fibers besides the generally expected circular cross-section and smooth surface topology. Also, it is found that smooth fibers with highly porous interiors can be formed in a humid environment. The resulting external topographies and internal morphologies result from a competition amongst the dynamics of phase separation, the rate of solvent evaporation, and a buckling instability. For example, in the presence of high humidity, the formation of interior porosity in polystyrene (PS) fibers electrospun from solutions in dimethylformamide (DMF) is attributed to the relatively rapid diffusion of water vapor into the jet, leading to a liquid-liquid phase separation that precedes solidification. In the presence of low humidity, the fibers exhibit a wrinkled morphology that can be explained by a buckling instability when the characteristic time of buckling precedes the drying time and the characteristic time for phase separation. The key to understanding this phenomenon is the formation of a thin glassy skin on the surface of the gel-like core during processing. Solvent evaporation leads to the rapid formation of a thin glassy shell. As solvent evaporation from the core proceeds, the core contracts and pulls radially inward on the stiff outer shell. The critical buckling conditions have been investigated as a function of modulus and Poisson’s ratio of the shell and core, thickness of the shell, and the radius of the fiber. By controlling the relative rates of evaporation of solvent from the shell and the core of the jet, the adsorption of nonsolvent from the environment, relative humidity, temperature, surrounding gas composition, the selection of polymer and solvent with regard to their interaction, the concentration of polymer, the molecular weight of polymer, the selection of the core and shell fluids in co-axial electrospinning, or different solvent combination for the evaporation, either porous or consolidated fibers and/or either smooth or wrinkled fibers can be produced in accord with the needs of specific applications. For example, hydrophilic or hydrophobic properties of mats can be enhanced because wrinkling imparts a second, finer scale roughness on top of the curved fiber surfaces.
12:30 PM - WW4.9
Impact of Fiber Length Scale on the Breakthrough Pressure for Non-wetting Textured Surfaces.
Shreerang Chhatre 1 , Anish Tuteja 1 , Wonjae Choi 2 , Joseph Mabry 3 , Gareth McKinley 2 , Robert Cohen 1
1 Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge , Massachusetts, United States, 2 Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Space and Missile Propulsion Division, Air Force Research Laboratory, Edwards Air Force Base, California, United States
Show AbstractRecent studies have shown that woven and non-woven fabrics composed of nanoscale fibers form good platforms for developing superhydrophobic and superoleophobic substrates. The wettability of a textured surface depends on the geometric details and length scales of the surface texture and the inherent wettability of the chemically-equivalent smooth surface. Surfaces which are strongly non-wetting to oil and other low surface tension liquids can be realized by trapping microscopic pockets of air within the asperities of a re-entrant texture, thereby generating a solid-liquid-vapor composite interface. For low surface tension liquids like hexadecane (γlv = 27.5 mN/m), the composite interface is at best metastable due to the low value of the equilibrium contact angle (θE). Thus, on application of a sufficient pressure difference (e.g. an externally applied pressure or a sufficiently large Laplace pressure from a small droplet) the metastable composite interface transitions to a fully-wetted interface. As the length scale of the re-entrant surface features is reduced (e.g. to electrospun polymer fibers) the robustness of the composite interface increases.We develop a design parameter framework to predict the apparent contact angle (θ*) and the breakthrough pressure (Pb) as a function of the equilibrium contact angle on a chemically identical smooth surface (θE), the physical properties of the contacting liquid and the geometric parameters of the surface texture. In this work, we use a set of self-similar wire meshes (i.e. with a constant spacing ratio D* = (R+D)/R = 2.45, where 2D, is the inter-wire spacing) with wire radii varying from R = 18 to 114 μm. The wire meshes are dip-coated with an assortment of conformal polymeric coatings which encompass a broad variation in solid surface energy (γsv) from about 10 to 30 mJ/m2. Apparent contact angle (θ*) and breakthrough pressure (Pb) are measured on this set of idealized surfaces and match favorably with the design parameter framework predictions. The breakthrough pressure (Pb) on the dip-coated wire meshes is found to vary inversely with the length scale of the texture. Consequently, similar textured surfaces with submicron or nano scale textures are expected to have very high breakthrough pressures (Pb). As a result, such surfaces can be used as membrane separators with controlled wettability and breakthrough pressure for different liquids.
12:45 PM - WW4.10
An Industrial Perspective on Surface Characteristics of Electrospun Nano/Micro fiber Mat.
H. Young Chung 1 , Doug Crofoot 1 , Andrew Dallas 1
1 Corporate Technology, Donaldson Co., Inc., Minneapolis, Minnesota, United States
Show AbstractElectrospinning, due to its processing characteristics, provides distinct features of nano-to-micro scale fiber diameters, spaces-in-between fibers and surface characteristics defined by fiber diameter, spaces-in-between, morphology and its chemical constituents. Tremendous progress has been made at MIT and elsewhere to enhance the hydrophobicity of electrospun nanofiber mats to achieve superhydrophobic and/or oleophobic properties. However, there are other aspects of surface characteristics are not fully explored yet. Authors wish to discuss other aspects of surface characteristics of nanofiber web from the view point of practical filtration/ separation applications.The term, surface characteristics, can be confusing as the word can mean different things to different people. Compatibility and surface reactivity are important characteristics for biological systems and where the nanofiber layer comes in contact with liquid.Tribology and surface electrical properties become important when a nanofiber mat is exposed to an air stream. Adsorption is critical when one needs to separate a fluid among other fluids. In the case of adsorption application, the surface areas of nanofibers provided by electrospinning, while being a few hundred times larger than conventional fiber, is not as large as that of activated carbon/catalyst structure.We will discuss those surface characteristics of nanofiber mat from the view point of filtration and separation aspects. In addition, we will suggest some areas for future research.
WW5: Structure-Property Relationships for Polymer Nanofibers
Session Chairs
Wednesday PM, December 02, 2009
Room 203 (Hynes)
2:30 PM - **WW5.1
Nanofibers by electrospinning – from fundamental research to real applications
Andreas Greiner 1 , Seema Agarwal 1 , Joachim Wendorff 1
1 Dept. of Chemistry, University of Marburg, Marburg Germany
Show AbstractA wealth of knowledge about nanofibers by electrospinning has been accumulated by the research community in the past decade [1,2]. These efforts also induced many fascinating ideas for applications of nanofibers. However, next to possible market problems, productions issues and lack of business models restricted the commercialization of many of these ideas till now. This contribution will discuss in detail on selected examples based on results of fundamental research problems and solutions on the way to commercialization of nanofibers by electrospinning. [1] A. Greiner, J. H. Wendorff, Angew. Chem. Int. Ed. 2007, 46, 5670.[2] S. Agarwal, A. Greiner, J. H. Wendorff Polymer 2008, 49, 5603
3:00 PM - WW5.2
Fiber Encapsulated Nanoparticle Arrays.
Nikhil Sharma 1 4 , S. Ismat Shah 1 2 , Sylvain Cloutier 3 4 , Darrin Pochan 1 4
1 Materials Science & Engineering, University of Delaware, Newark, Delaware, United States, 4 Delaware Biotechnology Institute, University of Delaware, Newark, Delaware, United States, 2 Physics & Astronomy, University of Delaware, Newark, Delaware, United States, 3 Electrical and Computer Engineering, University of Delaware, Newark, Delaware, United States
Show AbstractOne dimensional nanostructures exhibit anisotropy in their physical properties that renders them deployable in applications in magnetism and nano-scale photonics. Electrospinning is a versatile and robust method of producing extremely high aspect ratio 1D nanostructures. Herein, we present the construction of nanofiber encapsulated particle arrays via electrospinning. Highly aligned arrays of silica and iron oxide nanoparticles encapsulated within Poly(ethylene oxide) fibers have been fabricated and characterized by electron microscopy. Dichroism of the hybrid nanofiber arrays has been systematically tuned by controlling the extent of silica nanoparticle incorporation into the fiber matrix. In the case of magnetic nanoparticle arrays of iron oxide, anisotropic magnetic behavior was observed along different orthogonal axes (parallel and perpendicular to the fiber alignment axis), with a notable increase in the coercivity of the arrays in the parallel configuration.
3:15 PM - WW5.3
Technique to Measure Adhesive Forces Between Electrospun Nanofibers.
Qiang Shi 1 , Kai-Tak Wan 2 , Shing-Chung Wong 1 , Pei Chen 1 , Todd Blackledge 3
1 Department of Mechanical Engineering, The University of Akron, Akron, Ohio, United States, 2 Department of Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts, United States, 3 Department of Biology, The University of Akron, Akron, Ohio, United States
Show AbstractIn this study, we developed a technique and a mechanics model to measure the dry adhesive properties between electrospun nanofibers. Due to the difficulty in handling these nanofibers and measuring the contact areas, little is reported and understood on the dry adhesive forces between nanofibers. Of critical importance is the ability to mimic naturally occurring dry adhesion such as that between gecko's and spider's foot hairs and untreated surfaces using electrospinning-enabled techniques. The adhesion test was performed on two poly(ε-caprolactone) electrospun ultrafine fibers using a nanoforce tensile tester. The specimens were cut and exposed when mounted on trimmed cardboard sheets for gripping and testing. The contact area of fibers was determined independently by scanning electron microscopy (SEM). Two different geometries of fiber adhesion were characterized and evaluated. The adhesive forces between nanofibers were assessed as a function of fiber diameter. A theoretical model was constructed based on the elastic/viscoelastic behavior of the fibers and a thermodynamic energy balance between the energy stored in the deformed sample and the interfacial adhesion energy. The presence of long-range intersurface forces will be considered in this model. Other structural properties such as the degree of crystallinity, crystal and molecular orientations of the spun fibers will be reported using wide angle and small angle X-ray diffraction techniques. The effects of fiber diameter and crystallinity on dry adhesion will be discussed.
3:30 PM - WW5.4
Dynamic Mechanical Properties of Polystyrene and Elastomeric Block Copolymer Nanofiber Blend.
Sungwon Ma 1 , Yonathan Thio 1
1 Polymer, Textile and Fiber Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractThe dynamic mechanical properties of blend of neat polystyrene and two elastomeric block copolymer nanofibers as filler have been explored. The elastomeric block copolymer nanofibers are prepared by employing the phase separation property of polystyrene-b-polyisoprene copolymer. The block copolymer having cylindrical morphology is first self-assembled in the form of fiber and then exposed to crosslinking agent (S2Cl2) for cold vulcanization. The effect of processing conditions - such as centrifugation and crosslinking agents –on the morphology of nanofiber is also studied resulting in two elastomeric polymer nanofibers: fully crosslinked nanofiber (FCF) and fully crosslinked multi-junctioned nanofiber (FCM). For comparison with these nanofibers, partially crosslinked multi-junctioned sample (PCM) and uncrosslinked PS-PI block copolymer (UCB) have been investigated as well. The crosslinking density is calculated by measuring the change in intensity of the double bond peaks using FT-IR spectroscopy. The blends are prepared by solvent casting by mixing neat polystyrene and four nanofillers: FCF, FCM, PCM, UCB. The thermo-mechanical properties and morphology of the blends were characterized by dynamic mechanical analysis (DMA) and scanning electron microscope (SEM). DMA results show that the modulus increase with increasing filler loading in the terminal region in case of both PS/FCM and PS/FCF systems and the increasing rate is related to the crosslinking density. Another interesting observation was obtained from PS/FCM blend where the Tg is decreased from that of pure PS and the moduli decreased with the increase in filler content below Tg of neat PS. These results are interpreted in terms of the effects of crosslinking density and the free volumes of fillers in blends.
3:45 PM - WW5.5
Nanofiber Formation Through Conducting Polymer Self-assembly for Energy Applications.
Yeng Ming Lam 1 , Teddy Salim 1 , Shuangyong Sun 1 , Chris Boothroyd 2 , Lydia Helena Wong 1
1 School of Materials Science and Engineering, Nanyang Technological University, Singapore, Singapore Singapore, 2 Centre of Electron Nanoscopy, DTU, Kongens Lyngby Denmark
Show AbstractNanoscale assemblies are the result of many physical and chemical factors. Some of these factors are the interaction energies (polymer/ polymer, polymer/solvent), the physical properties of the solvent and the chemical structures of the polymers. Detailed understanding of the factors involved in the control of these structures will enable us to design different types of supramolecular assemblies.In some organic solar cell devices, it is well known that an ordered morphology is essential for charge transport. This is to provide continuous pathways for electrons or holes to travel to the electrodes. Conventionally this organization is attained using thermal annealing. However for polymeric substrates, annealing is less desirable. Here, we will report our work using alkylmercaptane and alkylbromide-based “poor solvents” in morphology modification and how the chemical structure and host solvent affects the morphology. We will also show how one dimensional nanofibers can be achieved for thiophene-based polymers and how the chemical structure affects the film organization and properties, the morphology and the device properties. Other critical factors for controlling nanofiber growth are the solvent, the concentration and the cooling rate. We also make use of these thiophene based nanofibers in solar cells and are able to obtain good power conversion efficiencies. This solution-based, pre-treatment method provides a good alternative to thermally annealing the thin film for solar cell applications. On top of this, we are also working on gaining some understanding and control of the organization of the thiophene-based molecules which may also help in the understanding and controlling the organization of other conjugated polymers.
4:00 PM - WW5:Properties
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4:30 PM - **WW5.6
Continuous Nano-Scaled Carbon Fibers with Superior Mechanical Strength.
Hao Fong 1
1 Department of Chemistry, South Dakota School of Mines and Technology, Rapid City, South Dakota, United States
Show AbstractContinuous nano-scaled carbon fibers can be developed by stabilization and carbonization of highly aligned and extensively stretched electrospun polyacrylonitrile copolymer nanofiber precursor under optimal tension. These carbon fibers with diameters being tens of nanometers would possess a superior mechanical strength which is unlikely to be achieved through conventional approaches. This is because (1) the innovative precursor, with fiber diameter approximately 100 times smaller than that of conventional counterparts, would possess an extremely high degree of macromolecular orientation and a significantly reduced amount of structural imperfections; and (2) the ultra-small fiber diameter would also effectively prevent the formation of structural inhomogeneity particularly sheath-core structures during stabilization and carbonization.
5:00 PM - WW5.7
Thermo-mechanical Behaviors of the Carbon Nanofiber Filled Polyethylene- oxide.
Ananta Adhikari 1 , Karen Lozano 1 , Mircea Chipara 2
1 Department of Mechanical Engineering, University of Texas-Pan American, Edinburg, Texas, United States, 2 Department of Physics and Geology, University of Texas-Pan American, Edinburg, Texas, United States
Show AbstractThermal and mechanical properties of Carbon nanofiber (CNF) filled polyethylene oxide (PEO) composites along with neat PEO were studied using Thermogravimetric analysis (TGA), Dynamical Mechanical Analysis (DMA) and Differential Scanning Calorimetry (DSC). TGA and DMA analysis showed a gradual increase of thermal stability and mechanical behavior of polymer with the filler content. Crystallization kinetic analyses demonstrate the strong temperature dependence crystal growth. Crystal nucleation activity is presented based on Lauritzen-Hoffman (LH) nucleation theory and is in agreement with the value of crystallization activation energy.
5:15 PM - WW5.8
Time and Strain Rate Mechanics of Polymeric Nanofibers.
Mohammad Naraghi 1 , Ioannis Chasiotis 1
1 Aerospace Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractThe viscoelastic/plastic and failure properties of electrospun polyacrylonitrile (PAN) nanofibers were investigated at quasi-static and intermediate strain rates (10-4 - 200 s-1) as a function of their fabrication parameters by using a novel, MEMS-based, experimental method for traceable nanoscale metrology. The nanofiber true ultimate strength was as high as 900 MPa, while the fiber ductility for the same strength values exceeded 300% for some of the fabrication conditions. The elastic modulus and the tensile strength of PAN nanofibers with diameters between 200-800 nm varied by a factor of seven with nanofibers in the range of 200-300 nm having the highest strength and stiffness. Spectroscopy showed that the thinner fibers, which demonstrated higher mechanical strength, were characterized by significant molecular alignment. The flow instabilities occurring during part of the electrospinning process were found to control the molecular alignment in the nanofibers, therefore directly affecting the uniformity in fiber extension during cold drawing. The mechanical response of the PAN nanofibers as a function of the applied strain rate was monotonic at rates 10-2 - 200 s-1. Given this strong strain rate sensitivity of the particular nanofibers, creep experiments with single nanofibers were also conducted. In agreement with the strain rate experiments and the aforementioned fiber diameter size effects, the creep compliance of thinner nanofibers (200-300 nm) was five times smaller than that of the thicker fibers (600-800 nm). Semi-empirical models were proposed to capture the viscoelastic/plastic response of the PAN fibers. The application of these calibrated models to predict the nanofiber mechanical response at slow strain rates was in very good agreement with our experiments.
5:30 PM - WW5.9
Mechanical Properties of Electrospun Nylon-6 Nonwoven Fabrics.
Chunhui Xiang 1 , Margaret Frey 1
1 Department of Fiber Science and Apparel Design, Cornell University, Ithaca, New York, United States
Show AbstractThe influence of fiber strength and fiber-fiber cohesion on mechanical properties of electrospun nylon-6 nonwoven fabrics was investigated. Carbon nanotubes were used as a reinforcing phase to improve mechanical properties of fibers by acting as a physical reinforcement and as a nucleation agent to increase overall crystallinity of fibers. Fiber –fiber cohesion was influenced by solvent bonding and thermal annealing strategies. Ten percent by weight and twenty percent by weight of nylon-6 in 88% formic acid concentrations were electrospun into one sheet of nonwoven fabrics by parallel electrospinning. Beaded fibers electrospun from 10% nylon-6 acted as adhesives to improve the mechanical properties. Cohesion between as-spun fibers was also modified by changing the spinneret to collector distance during the spinning process. Both fiber strength and cohesion were increased by subjecting the electrospun nylon 6 non-woven fabrics to free and constrained annealing at 65 celcius for 12 hrs. This annealing process reduced internal stresses (decrease shrinkage) and increased crystallinity and crystalline alignment within fibers.
Symposium Organizers
John F. Rabolt University of Delaware
Gregory C. Rutledge Massachusetts Institute of Technology
Bruce Chase DuPont Central Research
Joachim Wendorff Philipps University
WW6: Chemical and Surface Modification of Polymer Nanofibers
Session Chairs
Greg Rutledge
Corinne Wittmer
Thursday AM, December 03, 2009
Room 203 (Hynes)
9:45 AM - WW6.1
Functionalized Electrospun Textiles for Chemical and Biological Protection.
Liang Chen 1 , Lev Bromberg 1 , Heidi Schreuder-Gibson 2 , Phillip Gibson 2 , T. Alan Hatton 1 , Gregory Rutledge 1
1 Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 , U.S. Army Natick Soldier Research,Development & Engineering Center, Natick, Massachusetts, United States
Show AbstractProtective clothing systems in current use are primarily based upon full barrier protection by physically or chemically adsorbing all the toxins on the surfaces of fabrics. Current protective multilayer fabric systems are bulky and possess low moisture vapor permeability. Electrospun fabrics are remarkable for their breathability, light weight and high specific surface area, the last of which can be used to make the material highly reactive by the attachment of functional compounds. Such fabrics are promising candidates for use in the next generation of chemical and biological protection clothing, filters and masks. As proof of principle, we describe electrospun fiber mats functionalized with amidoxime groups, obtained either by electrospinning polymer blends containing polyacrylamidoxime, or by surface oximation of prefabricated polyacrylonitrile fiber mats. Amidoxime groups are reactive in degradation of organophosphate nerve agents and pesticides. For protection against bacterial contaminants, bactericidal fiber mats were produced by the electrospinning of polymer blends containing a biocide, chlorhexidine (CHX), with the capability to kill bacteria not only through a gradual release of unbound CHX from the fibers but also via contact with CHX bound to the fibers. In addition, multifunctional electrospun fiber-based fabrics for both chemical and biological protection were achieved via layer-by-layer electrostatic assembly of a reactive polyanion, polyhydroxamic acid, which serves to decompose nerve agents, and a bactericidal polycation, poly (N-vinylguanidine) onto prefabricated electrospun fibers. The capability of these functionalized protection fabrics to detoxify representative chemical and biological agents and their mimics is demonstrated. The breathability of the functionalized electrospun fiber-based systems is also addressed.
10:00 AM - WW6.2
Controllable Chemical Modification of Polyaniline Nanofibres.
Emer Lahiff 1 , Carol Lynam 2 , Niamh Gilmartin 2 , Gordon Wallace 3 , Richard O’Kennedy 2 , Dermot Diamond 1
1 CLARITY: The Centre for Sensor Web Technologies, Dublin City University, Dublin 9 Ireland, 2 School of Biotechnology and Biomedical Diagnostics Institute, Dublin City University, Dublin 9 Ireland, 3 ARC Centre of Excellence for Electromaterials Science, Intelligent Polymer Research Institute, Wollongong, New South Wales, Australia
Show AbstractPolyaniline (PAni) is an example of a stable conducting polymer whose properties (optical/electrical) change in response to the immediate environment of the material. PAni thus has huge potential in sensor applications. By focusing on PAni nanofibres we can increase the surface area exposed to molecules which are to be detected, thus enabling enhanced sensitivity and improved response times [1]. Our focus is on the covalent modification of these structures post-polymerisation. This can be achieved while simultaneously maintaining the intrinsic nano-morphology of the polymer material. Functionalisation is achieved by a quick and scalable reflux process, and both amide and carboxylic acid side-groups can be attached. The modified nanofibres maintain their ability to switch between different forms displaying distinctly different properties (as shown by UV-vis spectroscopy), thus making them suitable for adaptive sensing applications [2]. Using the technique described, control over the extent of functionalisation can be achieved [3]. The resulting material is characterised using electron microscopy, nuclear magnetic resonance, cyclic voltammetry and a range of spectroscopic techniques. Functionalised PAni nanofibres can then be used as templates for further modification, thus improving the selectivity of PAni. In particular we have demonstrated the subsequent attachment of biomolecules, whereby resulting PAni-antibody conjugates have applications in the field of electrochemical immunosensors. [1] Huang, J. X.; Virji, S.; Weiller, B. H.; Kaner, R. B., Polyaniline nanofibers: Facile synthesis and chemical sensors. Journal of the American Chemical Society 2003, 125, (2), 314-315.[2] E. Lahiff, S. Bell, D. Diamond, Functionalised Nanostructured Polyaniline – A New Substrate for Building Adaptive Sensing Surfaces. Mater. Res. Soc. Symp. Proc. 2008, 1054, 1054-FF05-05.[3] E. Lahiff, T. Woods, W. Blau, G.G. Wallace, D. Diamond, Synthesis and characterisation of controllably functionalised polyaniline nanofibres. Synthetic Metals 159 (2009), 741-748.
10:15 AM - WW6.3
Chemistry before and after electrospinning
Seema Agarwal 1 , Christian Brandl 1 , Fei Chen 1
1 , University of Marburg, Marburg Germany
Show AbstractElectrospinning is in general done by the use of soluble or meltable polymers [1,2]. Next to other parameters molecular characteristics such as molecular weight, molecular weight distribution, stereochemistry, degree of branching etc. could have a significant effect on fiber dimensions and fiber morphologies and thereby on properties of nanofiber-based nonwovens. Further, a wealth of possible chemical modifications of these nanofiber-based nonwovens can widen their property profile in nearly any direction. This contribution will discuss in detail on selected examples chemical issues of polymers used for electrospinning as well as chemical modification of electrospun nonwovens for property modifications.[1] A. Greiner, J. H. Wendorff, Angew. Chem. Int. Ed. 2007, 46, 5670.[2] S. Agarwal, A. Greiner, J. H. Wendorff, Adv. Funct. Mater., in press.
10:30 AM - WW6.4
Actuating Electroactive Fibers From Alkoxysilane Functionalized Polyferrocenylsilanes.
Jeffrey McDowell 1 , Ian Manners 1 , Geoffrey Ozin 2
1 Chemistry, University of Toronto, Toronto, Ontario, Canada, 2 Chemistry, University of Bristol, Bristol United Kingdom
Show AbstractCrosslinked conductive polymer networks that mediate chemical, electronic and mechanical signals are enticing materials from which to construct actuators and sensors as well as more complex polymer fiber based structures capable of emulating natural skeletal muscle. We have recently synthesized and characterized a novel class of high molecular weight electroactive polyferrocenylsilane (PFSs) that has been functionalized with pendant alkoxysilane groups and which can be conveniently gelled by sulfonic acid catalyzed condensation of the crosslinkable alkoxysilanes. PFS electroactive gel are capable of converting an electrical signal to mechanical stress and strain as a result of a change in dimension in response to electrochemical oxidation or reduction coupled with transport of charge balancing ions and solvent molecules. Other gelators include the common photoacid generator (PAG), triphenylsulfonium triflate. PFS gel microstructure can therefore be created photolithographically. Such microstructors can potentially be useful in organic electronics or can function as electroactuating microvalves and pumps in microfluidic applications. Interest in electronically tuning surface wettability via the so-called lotus effect has led to our creation of microstructured surfaces consisting of our polymer which can swell and contract. In contrast to polyaniline (PANI) and polypyrrole (PPy), high solubility and high molecular weight PFS enable electrospinning solutions of these polymers into electroactive gel microfibers. There is no need to electrospin PFS as part of a blend with high molecular weight nonconductive polymers or use nonconductive fibers as templates for PANI or PPy polymerization. , Using a 5kV voltage applied between the needle and ITO substrate, fibers can be produced and collected. ITO substrates are incorporated into miniature electrochemical cells containing lithium triflate/γ-butyrolactone electrolyte and examined using optical microscopy. Applying 2.0V anodic potential to the ITO results in immediate oxidation of PFS fibers followed by strain induced buckling. Buckling occurs in many cases as regular sinusoid perturbations along the fiber and is reversible. Application of cathodic 2.5V potential causes most of the distorted fibers to return to their initial form. Such inherent shape memory is potentially useful in creating microswitches, microactuators and micromanipulators.
10:45 AM - WW6.5
Nanogel-Functionalized Polymeric Nanofibers.
Qichen Wang 1 , Chandra Valmikinathan 2 , Xiaojun Yu 2 , Matthew Libera 1
1 Department of Chemical Engineering and Materials Science, Stevens Institute of Technology, Hoboken, New Jersey, United States, 2 Department of Chemistry, Chemical Biology, and Biomedical Engineering, Stevens Institute of Technology, Hoboken, New Jersey, United States
Show AbstractThe fabrication of polymeric nanofibers by electrospinning has been used to form fibrous matrices that may closely mimic the structure of the extracellular matrix (ECM) in biological tissue. The length scales afforded both by the nanofiber diameter and the average inter-fiber spacing are consistent with those required by subcellular signal transduction in a range of biological tissue. This fibrous alternative to native ECM may provide the necessary early cues to support cell invasion and tissue regeneration as demonstrated by many investigators. We have been studying a range of polycaprolactone (PCL) based fibers, and we have shown that these nanofibers are suitable matrices for musculoskeletal tissue engineering and neural tissue engineering, as demonstrated by promoting cell attachment, proliferation and differentiation of osteoblast cells and stimulating neurite outgrowth from neuronal cells. To further control the surface properties of the nanofibers, we are exploring the functionalization of nanofiber surfaces using self-assembled nanohydrogels. We synthesized hydrogel particles with diameters ranging from about 50 – 500 nm by the copolymerization of PEG diacrylate (PEGDA) with acrylic acid (AA) dissolved in dichloromethane and dispersed as an emulsion in water. Our initial experiments have avoided surfactants. The acrylic acid provides charged groups that facilitate electrostatic self-assembly as well as sites for post-polymerization chemical functionalization. The resulting gels display pH responsiveness and swell by a factor of 6-12 times. To introduce a positive charge on the PCL-based nanofibers, chitosan was blended into PCL, and the polymeric blended nanofibers were prepared through electrospinning. Hydrogel particles were deposited onto the nanofibers by soaking nanofiber mattes in colloidal solution of gel particles in PBS at pH 7.4 overnight followed by repeated washing in PBS and deionized water. The scanning electronic microscopy (SEM) imaging of dried mattes shows nanofiber surfaces with attached gel particles. The particles tend to accumulate at nanofiber triple junctions suggesting that drying may reorganize the gel distribution. We tested the bioactivity of these nanogel-functionalized nanofibers with the osteoblast cells and neuronal cells. The results indicated that the nanogel functionalized nanofibers supported the attachment of osteoblast cells and stimulated neurite outgrowth from neuronal cells. The nanogel functionalized nanofibers have potential applications in tissue engineering and infection control. They bring the opportunity to provide further cues for ECM mimics, to control surface roughness, enable the delivery of growth factors, and create growth-factor gradients to guide cellular response and tissue formation, and provide new mechanisms to repel opportunistic bacteria and increase the infection resistance of a synthetic tissue scaffold.
11:00 AM - WW6: Chemical
BREAK
11:30 AM - WW6.6
Writing Polymer Nanofibers on Superhydrophobic Surfaces for the Directed Deposition of 3D Nanowire Surface Structures.
Benjamin Hatton 1 , Laurent Corbin 2 1 , Howard Stone 1 , Joanna Aizenberg 1
1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 2 IPR - UMR, UR1-CNRS, Rennes, Bretagne, France
Show AbstractAn aqueous droplet on a superhydrophobic nanopost array is only exposed to the very tips of the post structures, and therefore material deposition from solution can be limited to those selective areas. Herein we demonstrate a novel method for the directed writing of polymer nanofibers from a droplet solution of polyvinyl alcohol (PVA) on the posts of a superhydrophobic array of Si posts (300 nm diameter, 6 – 8 um tall, pitch spacing 1-4 um), etched by deep reactive ion etching [1]. Highly uniform, parallel strands of PVA nanofibers with diameter ~ 50 nm have been ‘drawn’ from solution to connect the posts, in a rapid, room temperature process, by translating a droplet over the non-wetting surface. A motorized XY stage was used to control the movement of a droplet at the end of a syringe tip along specific directions. The fiber formation depends on the polymer concentration, droplet speed, and surface functionalization, to form stable fibers at the receding edge of a mobile droplet in the Cassie (non-wetting) superhydrophobic state, under conditions of high shear rates. We have developed a model for the formation mechanism as a balance of the viscosity, surface tension, the pulling speed, the rate of solvent evaporation and the post array geometry. We show that this approach is general and is widely applicable to the directed deposition of a range of fibrous materials. In particular, it has been applied to the deposition of multi-walled carbon nanotubes, and collagen fibers. Since this method provides a means to connect specific posts together with nanofibers along controlled directions, it could be applied to the design of nanoelectronic structures and 3D nanostructures. In addition, such polymer nanofibers could be used as a template for vapor deposition, inorganic mineral growth from solution and directed adhesion of biological cells.[1] Krupenkin, T. N.; Taylor, J. A.; Schneider, T. M.; Yang, S., Langmuir 2004, 20, 3824-3827.
11:45 AM - WW6.7
In Situ Crosslinking of Electrospun PVA Nanofibers.
Christina Tang 1 , Carl Saquing 1 , Jonathon Harding 1 , Saad Khan 1
1 Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina, United States
Show AbstractWe examine a single step reactive electrospinning of polyvinyl alcohol (PVA) and a chemical crosslinking agent, glutaraldehyde (GA) with a catalyst, hydrochloric acid (HCl) to generate water insoluble PVA nanofibers. Crosslinked hydrophilic membranes such as nanofibrous membranes of chemically crosslinked PVA have potential applications for separation of organic-water mixtures by pervaporation. The development of a single-step process to crosslink electrospun fibers may accelerate the crosslinking processes by eliminating the need for post-electropinning treatment. The rheological properties of PVA solutions were studied and correlated with electrospinnability. The reactive electrospinning process lowered the critical PVA concentration required for successful electrospinning of the system. During in situ crosslinking, significant changes in rheological properties occurred and these were monitored in parallel with electrospinning. By measuring the dynamic rheological properties simultaneously, we associated changes in rheological properties to changes in fiber morphology for two regimes: (1) below the critical concentration to electrospin pure PVA and (2) above the critical concentration to electrospin pure PVA. In regime (1) fiber morphology changed from beaded fibers to uniform fibers to flat fibers and in regime (2) fiber morphology changed from uniform fibers to flat fibers. The electrospinning windows to generate uniform fibers for both regimes could be manipulated by changing the molar ratio of GA to PVA and the volume ratio of HCl to GA. Fibrous material was insoluble in water and the uniform fiber morphology could be maintained after soaking in water overnight. The critical molar ratio of GA to PVA and volume ratio of HCl to GA to crosslink 7 wt.% PVA and maintain fibrous morphology were determined.
12:00 PM - WW6.8
Poly(3,4-alkylenedioxythiophene) Nanostructures.
A.Sezai Sarac 1
1 Chemistry , Istanbul Technical University, Istanbul Turkey
Show AbstractElectrochemical coating of electroactive polymeric nanostructures on carbon substrates as nanoporous structure can increase the surface area, to obtain such structures polymer support and polymer electrode interfaces should be well defined . Nanostructured Poly( 3,4- propylenedioxythiophenes) (PProDOT) have exhibited high surface area and faster diffusion rates of ions into the nanostructures,which can be used in the Electrochemical capacitor( supercapacitor) applications.Supercapacitors are unique devices exhibiting greater capacitance than conventional capacitors, due to combination of the double-layer capacitance and pseudocapacitance associated with the participation of adsorbed intermediates in the surface redox-type reactions,showing high cycle life and stability, with useful electronic applications.Capacitor behavior of Single Carbon Fiber Microelectrode (SCFME) can be significantly enhanced by the formation of carbon/conjugated polymers as nano and microcomposites by electropolymerization of ProDOT, such system can represent a very well-defined region of pseudocapacitance properties because of the Faradaic redox reactions of their rich surface functionality.Higher energy densities can be achieved due to charging occuring through the small volume of material.Experimental conditions play important role on the final properties of modified CFMEs .The efficiency of the electropolymerization on carbon fiber surfaces under cyclovoltammetric conditions can be evaluated, i.e., scan rate, scan number, yield and morphology .Substituted PProDOT thin films have been cyclovoltametrically coated onto carbon fiber electrode to obtain an active functionalized microelectrode . In this presentation Electroactive Nanostructured PProDOT formations onto carbon fiber are reported . Evaluations of capacitor performance by electrochemical impedance spectroscopy and characterization of surface functionalities and surface morphology by FTIR reflectance, cyclic voltammetry(CV), and scanning electron microscope (SEM) are reported. Different pore structures were obtained by using different monomers ,the size of the cyclovoltametrically prepared polymeric pore structures was in the range of nm scale up to several hundreds nm by depending on the polymerization charge. Effect of the parameters on the capacitive behaviour of the substituted polyalkylenedioxythiophene coatings and on the morphology of films obtained by AFM and SEM was discussed. Capacitive behavior of the substituted PProDOT coated SCFME was investigated by CV in monomer free solution which was agreed with the capacitance obtained from electrochemical impedance spectroscopy. The electrochemical impedance data fitted to equivalent circuit models, used to find out numerical values of the proposed components. The dependencies of the equivalent circuit components of nanoscale structures at different experimental conditions are discussed.
WW7: Polymer Nanofibers for Medicine and Biology I
Session Chairs
Greg Rutledge
Corinne Wittmer
Thursday PM, December 03, 2009
Room 203 (Hynes)
12:15 PM - **WW7.1
Silk Nanofibers for Biomaterials.
Corinne Wittmer 1 , Thomas Claudepierre 2 , Xianyan Wang 1 , Christophe Egles 3 , Jonathan Garlick 3 1 , David Kaplan 1 3
1 Biomedical Engineering, Tufts University, Medford, Massachusetts, United States, 2 Ophthalmology, University of Leipzig, Leipzig Germany, 3 Cancer Biology and Tissue Engineering, Tufts University School of Dental Medicine, Boston, Massachusetts, United States
Show AbstractElectrospinning of silk proteins can proceed under controlled conditions to provide systematic insight into fiber features with many options to functionalize these nanoscale fibers. Since electrospinning of silk protein can be conducted using water as the solvent, the silk protein solution can be doped with bioactive components that retain their function during electrospining. For example, we have used this technique to generate electrospun silk mats containing epidermal growth factor (EGF) for the acceleration of wound healing. The EGF was incorporated into the silk mats during the spinning process and was released over a 48 hr period. In an in vitro model of wound healing, based on the use of human skin equivalents, the functionalized silk mats fostered healing by increasing the rate of wound closure of the epidermal tongue by 90 percent. The preservation of the structure of the mats during the healing period and the biocompatibility and slow degradation of the silk demonstrate that this system is a promising material for wound healing needs. Using a similar approach, silk electrospun fibers can serve as a cellular guide, to direct the outgrowth of nerve cells. In this case, the fibers provide a template along with the nerves grow, suggesting new options in nerve regeneration and in artificial circuitry. The strategies employed in these processes as well as the material features and biological outcomes will be reviewed to illustrate the versatility and potential utility of these nanoscale protein fibers in a range of medical applications.
12:45 PM - WW7.2
Electrospun and Natural Fibers Containing Biologically Active Components as Antibacterial Materials
Matthew Dickerson 1 , Maneesh Gupta 1 , Heather Luckarift 2 , Lawrence Drummy 1 , Glenn Johnson 2 , Rajesh Naik 1
1 Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright Patterson AFB, Ohio, United States, 2 Materials and Manufacturing Directorate, Air Force Research Laboratory, Tyndall AFB, Florida, United States
Show AbstractTextile materials capable of mitigating pathogenic bacteria and other potentially harmful biological agents are highly desirable and are under active development for use in filtration, protective equipment, high performance clothing, and wound dressings. We present results on the fabrication of antimicrobial fibers based on natural B. mori silk fiber and electrospun nanofiber architectures. The hybrid fibers produced in this work contain silver nanoparticles prepared through in situ synthesis techniques and were functionalized with antibacterial enzymes or peptides utilizing layer-by-layer processing strategies. The influence of peptide or enzyme loading, presence of silver nanoparticles, polyelectrolyte material selection, and electrospun fiber composition on the ability of these fibers to neutralize several strains of bacteria will be described. The efficacy of enzyme/peptide stabilization through layer-by-layer polyelectrolyte processing and the persistent antimicrobial activity of the resultant fibers were assessed under challenging environmental conditions and will be discussed in the context of the electrospun and B. mori fiber systems. The SEM and TEM characterization of the antibacterial fibers produced during the course of this study will be presented and factors impacting future textile development discussed.
WW8: Polymer Nanofibers for Medicine and Biology II
Session Chairs
Thursday PM, December 03, 2009
Room 203 (Hynes)
2:30 PM - **WW8.1
Electrospinning of Natural and Synthetic Polymers for Medical Applications.
Gary Wnek 1 , Olivier Arnoult 1 , Linghui Meng 1 , Bin Dong 1 , Meghan Greggor 2
1 Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, Ohio, United States, 2 Chemical Engineering, Case Western Reserve University, Cleveland, Ohio, United States
Show AbstractSignificant opportunities exist for the fabrication of materials having a useful biological function (e.g., enzyme activity) that are easily fabricated and utilized. Electrospinning has the requisite versatility to meet these requirements. Of particular interest has been the fabrication of collagen Type I scaffolds using electrospinning. We have found that benign solvents composed of water, alcohols and salts can afford collagen solutions suitable for electrospinning. Crosslinked collagen nanofiber scaffolds offer good mechanical properties and are being investigated as platforms for biological cell and tissue growth. We also have employed electrospinning of aqueous dispersions in polymer/organic solvent mixtures to afford non-woven matrices of polymers such as PLGA are rich with aqueous pockets containing water-soluble molecules for use as multi-functional scaffold materials for applications in regenerative medicine. Requirements of the scaffolds include serving as a mechanical support for cell delivery, the ability to deliver useful molecules (e.g., drugs, growth factors, enzymes, DNA), the ability to control porosity, and the ability to degrade within a desired timeframe. The utility of the ‘two-phase’ approach will be illustrated with selected applications in medicine.
3:00 PM - WW8.2
Single-step Electrospinning Towards Bimodal Fiber Meshes for Ease of Cellular Infiltration.
Rafael Gentsch 1 , Hans Boerner 1
1 , Max-Planck-institute of colloids and interfaces, Potsdam Germany
Show AbstractFiber meshes with bimodal size distribution, composed of micron and submicron sized fibers, which differ by one order of magnitude, can be obtained in a single-step process by electrospinning. A standard one syringe set-up was used to spin viscous poly(ε-caprolactone) and poly(lactic-co-glycolic acid) solutions in chloroform and mixed fiber meshes could be directly obtained by reducing the spinning rate at intermediate to high humidity. A mechanism for the formation of those meshes was proposed based on analysis of high speed camera images of the spin jet. Scanning electron microscopy (SEM) and mercury porosity of the meshes suggest a suitable pore size distribution for effective cell infiltration. While the micrometer fibers in the mixed meshes generate the open pore structure, the submicrometer fibers support cell adhesion and facilitate cell bridging of the large pores. This was revealed by initial cell penetration studies, showing superior ingrowth of epithelial cells into the hierarchical meshes compared to e. g. a mesh which was composed of unimodal roughly 1.5 micrometer thick fibers. Mixed mesh materials are promising, because they exhibit hierarchical pore/surface systems and combine two beneficial properties of one polymer at two different length scales. Therefore such nonwovens might not only be useful as scaffolds for in vitro tissue engineering, but also advanced filters will be possible, where nanofiber meshes increase the capture efficiency and microfibers provide porosity, preventing a drastic pressure drop. Moreover, catalyst supports could be generated, where rapid transport of the substrates and products require large pore structures and high catalytic activity makes large internal surfaces essential. Additionally, these fiber meshes might be interesting for drug delivery systems with different release kinetics given by the bimodality of the fiber diameter.
3:15 PM - WW8.3
Force Induced Alpha-helix to Beta-sheet Transition in Coiled-coil Protein Filaments: Process, Character and Critical Conditions.
Zhao Qin 1 2 , Markus Buehler 1 2 3
1 Laboratory for Atomistic and Molecular Mechanics, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Center for Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Center for Computational Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractHere we report a computational and theoretical study of the alpha-helix to beta-sheet transition in coiled-coil protein structures, a frequently observed mechanism of deformation in alpha-helix rich protein materials such as wool, hair, intermediate filaments and hoof. We observe the alpha-beta transition during the shearing process of coiled-coil protein domains. This transition, caused by mechanical force, leads to a stable conformation of beta-sheet, and absorbs loading energy at the same time. The resulting beta-sheet has an ultimate strength at the same level as natural beta-sheet materials. We propose a zipping model in describing the transition process for the secondary structure of the protein, in which the hydrogen bonds break and reform in the protein backbones. Using the Hierarchical Bell Model and existing experimental results, we carry out a theoretical analysis of the dependence of the alpha-beta transition on the length of the constituting alpha-helices. The result suggests that a coiled-coil with 33 amino acids in length is necessary to meet the critical condition to initiate the alpha-beta transition. For short peptides, the shearing force is not sufficient to induce the structural transition, while for long peptides, the transition can largely appear during mechanical deformation. We verify this result by 13 randomly picked coiled coils from the protein data bank, facilitated by a study of 170 molecular dynamics simulations. The simulation results, in agreement with the theoretical analysis, suggest this critical length is common to many coiled-coil proteins. Our work provides, to the best of our knowledge, the first explanation of such a transition that is widely found in the deformation of alpha-helix-rich protein materials. This research provides a linkage between the two most abundant secondary protein structures, and suggests a mechanical pathway to induce the transition. This may have interesting applications in the design of material with high stiffness, as well as high capacity of energy absorption.
3:30 PM - WW8.4
DNA Nanofiber Decontamination Membranes.
Daminda Navarathne 1 2 , Yogesh Ner 2 , Menka Jain 3 , James Grote 4 , Gregory Sotzing 1 2
1 Department of Chemistry, University of Connecticut, Storrs, Connecticut, United States, 2 Polymer Program, University of Connecticut, Storrs, Connecticut, United States, 3 Department of Physics, University of Connecticut, Storrs, Connecticut, United States, 4 , US Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio, United States
Show AbstractHighly ordered self assembly of the biological molecules has become an attractive tool for material scientists in designing advanced functional materials. One such example is complexes of DNA with surfactants or lipids with cationic head groups. Apart from their biological importance, these materials have emerged as an important class of optoelectronic materials. Surface modification of the DNA with surfactant leads to materials which can be easily fabricated into various morphologies, including electrospun nanofibers. The fabrication of high surface area nanofibers based on DNA enables an attractive material for decontamination filters. In particular, DNA has ability to specifically bind with wide range of materials, including DNA intercalators, heavy metal ions, polycyclic aromatic hydrocarbons (PAHs) etc. Utilizing this property of DNA combined with high surface area of the nanofiber, we will present their utility for designing efficient detoxification filter for DNA adduct forming harmful compounds. Furthermore, we will discuss formation of uniform DNA nanofibers by varying electrospinning parameters. It was observed that, morphology of DNA nanofibers is dependent on both the electrospinning parameters and molecular weight of DNA. By varying these parameters, we will demonstrate formation of beaded and non-beaded nanofibers. The decontamination efficiency of these nanofibers for both heavy metal ions and planar aromatic compound will be discussed. We will also emphasize the role of high surface area nanofibers in terms of decontamination efficiency by comparing it with thin film controls. Finally, we will discuss unique strategies to isolate nanofibers from the detoxified media. This aspect is particularly important for water purification application, where a trace quantities of contaminant needs to be removed.
3:45 PM - WW8.5
Poly (vinyl alcohol) and Milk Protein Nanofiber for Biomedical Applications.
Narahari Mahanta 1 , Yiwei Teow 1 , Suresh Valiyaveettil 1
1 Chemistry, National University of Singapore, Clementi Singapore
Show AbstractIn this work, we explored the preparation of nanofiber from polyvinyl alcohol (PVA) and milk protein incorporated with calcium carbonate (CaCO3) and magnesium carbonate (MgCO3) by electrospinning technique. The thermal properties of the nanofibers were characterized by thermo gravimetric analysis (TGA) and differential scanning calorimetry (DSC). Field emission scanning electron microscope (FESEM) studies revealed that when PVA was mixed with milk protein along with 50 wt% of CaCO3 or MgCO3, smooth nanofibers of 300-500 nm diameters were formed. The presence of CaCO3 and MgCO3 in the nanofiber was confirmed by X-ray powder diffraction (XRD) analysis. The cytocompatibility of electrospun composite nanofiber were evaluated using human lung fibroblasts (IMR-90). There was an increase in cell attachment with time for all the different fibers. However, the cell viability after a week showed that there was increase in cell density on PVA-Milk protein, PVA-CaCO3 and PVA-MgCO3 fiber over PVA fiber (control). Also there was an enhanced cell attachment on PVA-Milk/CaCO3 and PVA-Milk/MgCO3 fiber in the order of 1.5 to 2 fold. These results indicated that cytocompatibility of the nanofibers in presence of milk protein had better cell adhesion properties. This endorsed the fact that milk protein fibers could be a potential candidate for tissue engineering.
4:00 PM - WW8: Biomed II
BREAK
4:30 PM - **WW8.6
Effects of Fibrous Scaffold Alignment on Cardiovascular Cell Phenotypes in vitro.
Robert Akins 1
1 Biomedical Research, Nemours Foundation - A.I. duPont Hospital for Children, Wilmington, Delaware, United States
Show Abstract Controlling multicellular organization is a central goal in the design of biomaterials for tissue engineering. In particular, there is a need for materials that can induce cellular alignment in the engineering of cardiovascular tissues. The lateral alignment of muscle cells in the heart and many blood vessels is critical to function. The effects of alignment imposed by biomaterial scaffolds on the component cells of engineered tissues, however, are only partially understood. In the studies presented here, electrospun, biodegradable polyurethane (ES-PU) mats with either aligned or unaligned fibers were used as scaffolds to support primary cardiac ventricular cell cultures. Cells isolated from two-day old neonatal rats were grown on the ES-PU scaffolds and parallel tissue culture polystyrene controls. The ES-PU supported high-density cell cultures, and flow cytometric data showed that cell subpopulations remained stable for at least two weeks in culture when a high-potency, serum-free medium was used. The ES-PU cultures contained electrically-coupled, spontaneously contractile muscle with connexin-43 localized to points of cell:cell contact. The orientation of the ES-PU microfibers correlated with the multi-cellular organization of cultures such that aligned materials yielded highly-oriented cardiomyocyte groupings similar to those seen in mature ventricular tissue. Atrial natriuretic peptide (ANP) is a peptide hormone expressed predominantly in atrial myocytes in the mature heart. During development, ANP is also produced in immature ventricular cells; however, its production is down-regulated during tissue maturation. Mature ventricular mycoytes only produce ANP under pathologic conditions associated with ventricular hypertrophy and disruption of tissue organization. Since its production decreases with the structural maturation of the cardiac ventricle, ANP represents a useful marker for studying cardiac ventricular cell molecular phenotype. In our studies, ANP was significantly lower in cells grown on aligned ES-PU than in cells grown on either isotropic scaffolds or tissue culture polystyrene indicating that scaffold-imposed lateral cell alignment resulted in a more mature cell phenotype. We conclude that the physical organization of microfibers in ES-PU scaffolds impacts both multi-cellular architecture and cardiac cell phenotype in vitro.
5:00 PM - WW8.7
Synthesis Oxygen Generating Nanofibers with Antimicrobial Properties for Bone Implant.
Junping Wang 1 , Geoffrey Ng 1 , Yizhou Zhu 1 , Xiaojun Yu 1
1 , Stevens Institute of Technology, Hoboken, New Jersey, United States
Show AbstractA common cause of implant failure is infection. Implant surfaces tend to accumulate serum proteins, which promote bacterial growth and colonization and hence, infection. Complicating the matter is that the bacteria form biofilms, a complex glycocalyx which enmeshes the area surrounding them, shielding them from the immune system and antibiotics. Due to the presence of this biofilm, treatment of infections of this nature requires removal of the implant, debridement of the bone in which it is implanted, and extensive antibiotic treatments. This treatment comes at great cost to the patient, both monetarily and in terms of quality of life. Oxygen radicals are highly reactive can kill bacterial through the oxidation of proteins, inhibition of membrane transport processes and DNA damage resulting in mutagenesis. Hydrogen peroxide has been reported to repress the expression of biofilm regulator icaR , thus prevent the biofilm formation. Moreover this effect is still active at low concentrations of H2O2. This property may cause the minimum damage to surrounding host tissue in orthopedic surgery. In a recent study, oxygen generating scaffolds have also been fabricated with sustained oxygen release over an extended period of time for enhanced tissue survival under hypoxic conditions. However under normal conditions oxidative stress has been reported to be harmful to many cell types. In our study, we incorporate oxygen generating materials calcium peroxide within nanofibers, which can produce hydrogen peroxides in the reaction with water, in order to develop an implant coating materials with anti-biofilm activity, as well as facilitate tissue regeneration. Moreover, in order to alleviate the harmful effect of the oxidative stress on the osteoblast cells, ascorbic acid, an antioxidant were also added to protect the human osteoblast cells. The PCL nanofibers containing different ratio of calcium peroxide w/o ascorbic acid were fabricated using co-electrospinning technique. In the preliminary study, we have evaluated the cytotoxicity of the nanofibers to the human osteoblast cells by the MTS cell proliferation assay. Our results have shown that 1%CaO2 will not affect the osteoblast cell numbers, however when the concentration of CaO2 increased to a certain amount (5%), cell numbers will significantly decrease probably due to the oxidative stress. However, the addition of ascorbic acid was shown to significantly alleviate the oxidative stress caused cell death, thus enhance the cell survival rate. Our results have demonstrated that the oxygen generating nanofibers will serve as potential coating materials for bone implant application.
5:15 PM - WW8.8
Controlled Assembly of Biologically Inspired Arrays of Polymeric Fibers: Potential Applications.
Sung Kang 1 , Boaz Pokroy 1 , L. Mahadevan 1 , Joanna Aizenberg 1
1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Show AbstractIn nature, there are many interesting examples where high-aspect-ratio structures are utilized for responding to various stimuli. For example, the sea anemone uses its tentacles for sensing and actuation and the gecko controls adhesion to various surfaces using hierarchically assembled fibrous structures on its feet. In man-made materials, the fabrication of stable high-aspect-ratio structures is challenging, as lateral adhesion leads to their collapse and clumping. This has been considered as a detrimental effect in nano- and micro-fabricated devices. Recently, we have made efforts to understand the clustering and lateral adhesion of high-aspect-ratio structures and to use this understanding to control the process and induce tunable movement and assembly of nanoposts into non-trivial, but large-area, highly reproducible patterns [1]. A detailed study of the effect of various geometrical and mechanical parameters (such as the influence of the diameter, pitch, cross-section, and modulus of polymeric posts, as well as the symmetry of the post array) on the capillary-induced self-organization of a periodic array of polymeric nanobristles into chiral hierarchical clusters and their use in particle trapping and release will be discussed. Reference:[1] B. Pokroy, S. H. Kang, L. Mahadevan, J. Aizenberg, Science 323, 237-240, 2009.
5:30 PM - WW8.9
Biocompatible and Crystallizable Structures of Low Molecular Weight Poly(2-isopropyl 2-oxazolines) from Electrospinning.
Vasana Maneeratana 1 2 , Christina Diehl 1 , Helmut Schlaad 1
1 Colloid Chemistry, Max-Planck Institute for Colloids and Interfaces, Potsdam Germany, 2 Laboratoire de Chimie de la Matière Condensée de Paris, Université Pierre et Marie Curie, Paris France
Show AbstractInterests in stimuli-sensitive or ‘‘smart’’ polymers have fueled interests in researchers looking to design multi-functional biomaterials. Reference to smart polymers alludes to characteristics such as those exhibiting Lower Critical Solution Temperature (LCST) phase changes at body temperatures, such as poly(N-isopropyl-acrylamide) (P(Nipaam)) and poly(2-oxazolines). Other smart characteristics include that of self-assembly and crystallization, as seen specifically in poly(2-isopropyl 2-oxazolines) (PIPOX); wherein the latter polymer creates an arrays of complex structures. Once crystallized, these structures become immiscible with water. Additionally, PIPOX incorporates other features such as the crystallization behavior with functionalizable copolymers used towards sensing applications. Processing PIPOX with electrospinning is introduced as another facet for new nano-scale structures to take advantage of the biocompatible and smart features. The uses of extremely low molecular weight polymers are rarely discussed, but important for a variety of reasons such as the shortening the time from synthesis to production. Taking advantage of the low molecular weight batches, ranging from 3000 g/mol up to 27,000 g/mol, that can be produced in a day or less, we have focused on electrospinning these homo polymers to essentially produce another level of structural hierarchy as a low, molecular weight crystallizable biocompatible mat. The discussion will focus on crystallization studies and other morphological aspects. Long-range possibilities from these aspects include modulus tailoring of these mats to serve as biocompatible substrates towards the use in stem-cell differentiation, biodegradable implants, and biosensors.
5:45 PM - WW8.10
Electrospun Alginate-Based Nanofibers for Use as Tissue Scaffolds: Investigation of Single and Coaxial Needle Approaches.
Christopher Bonino 1 , Melissa Krebs 2 , Sung In Jeong 2 , Carl Saquing 1 , Kimberly Shearer 1 , Eben Alsberg 2 , Saad Khan 1
1 Department of Chemical & Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina, United States, 2 Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio, United States
Show AbstractBiocompatible nanofibers prepared by electrospinning are of interest as tissue engineering scaffolds. Electrospun nanofibrous mats have the potential to support cell adhesion and proliferation due to their high surface-to-volume ratio. Alginate is a natural biocompatible polysaccharide that has shown promise in regenerative medicine applications as a scaffold material. However, alginate has inherent material properties that prevent it from being electrospun in a pure state. Namely, alginate is an anionic polyelectrolyte in water and has charge repulsions which reduce its chain entanglements. To overcome this we use polyethylene oxide (PEO), a second biocompatible polymer. Nanofiber mats are prepared using two methods: (1) by blending alginate with PEO in single needle electrospinning or (2) with PEO as the sheath and alginate as the core in coaxial electrospinning. Electrospun mats are then treated by solutions containing calcium salts in order to crosslink the alginate and remove the PEO. Our preparation methods use biocompatible polymers and crosslinking agents, which more readily permits the use of the nanofiber mats as tissue scaffolds. In addition to these approaches, we will also discuss the feasibility of electrospinning alginate with different molecular weights (i.e., 37 kDa and 196 kDa) and relate the properties of the pre-electrospinning solutions to the fiber morphology.
WW9: Poster Session: Polymer Nanofiber
Session Chairs
Bruce Chase
John Rabolt
Darrell Reneker
Friday AM, December 04, 2009
Exhibit Hall D (Hynes)
9:00 PM - W9.34
Coaxial Electrospinning of Compound Elastomeric Polymer Fibers.
Andrew Steckl 1 , Daewoo Han 1
1 , University of Cincinnati, Cincinnati, Ohio, United States
Show AbstractElastomeric polymer microfibers have many applications, ranging from textiles for swimwear to medical grafts. Electrospinning is a versatile technique for the production of polymer nano/microfibers with diverse materials. Core-sheath structured or hollow nano/microfibers can be produced using the coaxial electrospinning method. Using the core-sheath structure, different properties from two different polymers are integrated into a single fiber.We have investigated coaxial electrospinning to produce core-sheath fibers incorporating elastomeric polymers. We have successfully produced various core/sheath structured fibers combining the elastomer polyurethane (PU - the key component in Spandex and Lycra) with polyamides (Nylon) and fluoropolymers (Teflon) using coaxial electrospinning. The average fiber diameter of coaxial PU/Nylon-6 fiber is ~ 2μm. Core diameter (~1.36μm) and sheath thickness (~325nm) have been evaluated by TEM images and theoretical calculation based on the volume of electrospun materials. Tensile strength and elasticity tests have been performed to compare the mechanical properties of coaxial fibers of various compositions. Coaxial PU/Nylon-6 fibers show ~60% elasticity recovery after 100% extension. The fiber morphologies associated with solvent selection have also been studied.Using coaxial fibers of PU core and Nylon-6 sheath, good elasticity from the PU core and superior toughness and abrasion resistance from the Nylon-6 sheath can be obtained. Superhydrophobic textiles also have been demonstrated with the PU or Nylon-6 core and Teflon sheath materials, showing an average water contact angle of 158° and rolling-off angle of 7°.Coaxial electrospinning of elastomeric polymer fibers is a very promising approach that enables the fabrication of core-sheath structured nano/microfibers with very interesting and unique features.
9:00 PM - WW9.1
Reinforcing Efficiency of Epoxy Resin by 4-(Aminophenoxy)Benzoyl-functionalized Carbon Nanotubes and Carbon Nanofibers.
Kyungsu Kim 1 , Inyup Jeon 1 , Jongbeom Baek 1
1 , ulsan national institute of science and technology, Ulsan metropolitan city Korea (the Republic of)
Show AbstractEpoxy/carbon nanotube (CNT) composites have been extensively investigated due to they could be useful for bulk applications. The enhancement of mechanical properties and electrical conductivity of epoxy/CNT composites depend primarily on the homogeneous dispersion of CNT into epoxy matrix and the interfacial interactions between the components. Although the dispersion of CNT into supporting matrices such as solvents, polymers and inorganic materials has been studied last two decades, it is still remaining challenge due to the homogeneous dispersion of CNT without damaging its framework. Hitherto, the best option should be the chemical functionalization of CNT with minimum damage to provide chemical affinity to supporting matrices.Epoxy or polyepoxide is a thermosetting polymer formed from reaction of an epoxide resin with polyamine as hardener. Epoxy is the most widely used adhesives including fiber-reinforced plastic materials and general purpose adhesives. Epoxies have excellent adhesion, chemical and heat resistance, excellent mechanical and very good electrical insulating properties. By introducing additives into epoxy resin, many properties can be modified. For example, silver-filled epoxies show good electrical conductivity. However, the drawback is the cost and interfacial bonding between epoxy and silver particles.As an alternative, CNT has received much attention due to their expected outstanding mechanical and electrical properties. However, to effectively deliver its properties to supporting matrices, aforementioned two issues have to be resolved first when it is used as nanoscale reinforcing additive. Hence, vapor-grown carbon nanofibers (VGCNF) and multi-walled carbon nanotubes (MWNT) were functionalized with custom synthesized 4-(4-aminophenoxy) benzoic acid in polyphosphoric acid (PPA)/phosphorous phentoxide (P2O5) medium via “direct” Friedel-Crafts acylation reaction. The resultant 4-(aminophenoxy)benzoyl-functionalized VGCNF (AB-VGCNF) and MWNT (AB-MWNT) were blended with epoxy resin by simple mechanical stirring in dichloromethane, which was added to help efficient mixing. The thermal, mechanical and electrical properties of the nanocomposites were studied with respect to AB-VGCNF or AB-MWNT loads.
9:00 PM - WW9.10
Elongational Rheology of Electrospinning Jets.
Hyungjin Lee 1 , Darrell Reneker 1
1 Polymer Science, University of Akron, Akron, Ohio, United States
Show AbstractA new method for measurement of longitudinal stresses in an electrospinning jet was introduced [1]. An improved elongational rheometer, with a shorter displacement pulse permits measurements to be made in the region closer to the flow modified Taylor cone, where the elongational stress is large, and the change in stress with position is quite rapid. With a shorter pulse, data on pulse position and width are obtained with higher precision. The range of longitudinal stresses that can be measured is larger. 1. T. Han, A. L. Yarin and D. H. Reneker, Polymer. 49, (2008) pages 1651-1658.
9:00 PM - WW9.11
Illumination of an Electrospinning Jet and Its Characterization Using Videography and Stereography.
Kaiyi Liu 1 , Darrell Reneker 1 , Camden Ertley 1
1 Polymer Science, University of Akron, Akron, Ohio, United States
Show AbstractThe relationship between lighting arrangements and the visual images of an electrospinning jet was determined, and then was used to characterize the path of the jet. The jet was illuminated with both a steady intense beam of light coming from below and to the left, and from a short, intense flash light behind and above the jet. A digital video camera was used to observe and record the jet stereoscopically through a pair of prisms. Some frames of the video contained images provided by both the steady light and the flash. The analysis of the stereographic images showed that the instantaneous jet path was the path described in the Reneker-Yarin model[1,2]. The envelope cone ordinarily seen consists mostly of moving glints of the steady light reflected from the surface of segments of the jet. For a particular arrangement of one beam of light and one viewing direction, all of the glints observed occur on parallel tangents to the surfaces of the segments. Computer modeling was used to show how the glint trace bifurcated at the onset of the bending instability. The stereographic images of glint traces provided information to determine the velocities and positions, in 3-dimensional space, of selected segments of a jet. The electrical bending coils of an electrospinning jet decelerate along the vertical direction. Strategies for placement of additional lights to illuminate dark segments of a jet when using one camera were developed. “Stopped motion” paired stereographic images produced by the flash light revealed the handedness of the coiled path of an electrospinning jet, while the observation of glint traces, produced when a particular arrangement of beams of continuous light were used, permitted real time determination of the handedness of the jet using only observations made by eye. Changes in handedness of a coiled jet were frequently observed.[1]. D.H. Reneker, A.L. Yarin, Polymer, Vol. 49, (2008) pp 2387-2425. [2]. D.H. Reneker, A.L. Yarin, E. Zussman, H. Xu, Advances in Applied Mechanics, Vol. 41 (2006) pp 43-195.
9:00 PM - WW9.12
Extraction and Characterization of Cellulose Whiskers from Commercial Cotton Fibers.
Eliangela Teixeira 2 , Mariselma Ferreira 1 , Maria Alice Martins 1 , Ana Carolina Correa 2 , Luiz Henrique Mattoso 2
2 LNNA, Embrapa Instrumentaçao Agropecuária, Sao Carlos, SP, Brazil, 1 CCNH, UFABC, Santo André, SP, Brazil
Show AbstractDuring the last years there has been a growing interest in incorporating cellulose whiskers as nanoreinforcement in polymer matrixes [1]. The purpose of this study is to evaluate the performance of the cellulose whiskers obtained from commercial cotton. In this sense, cellulose whiskers were prepared by acid hydrolysis of commercial cotton fibers. The acid hydrolysis was carried out with sulfuric acid solution 6.5M at 45 °C and at 60 °C under vigorous stirring for 20 min and 75 min. The resulting suspension was neutralized by dialysis and the cotton whiskers were dried using an oven and freeze drying. Chemical composition of cotton fibers was found to be cellulose 88.3% ± 0.3, hemicellulose 8.0% ± 0.3 and lignin 4.8% ± 0.5. Cotton whiskers, which were dried using a freeze drier showed high thermal stability than those dried in an oven. The TG curves of cotton fibers showed an initial peak between 50 and 100°C due the vaporization of water. After this peak, in inert atmosphere, TG curve has only one large plateau and the DTG curve has one degradation peak at 300 °C due to the thermal depolymerization of hemicellulose, lignin, and α-cellulose decomposition (wt loss 80%). The X-ray diffractograms of cotton fibers and cellulose whiskers showed three peaks for all samples at 2θ = 16°; 22.6° and 34.7°. These are characteristic of the crystal polymorph I of cellulose. The peak at 2θ = 16° correspond to the (110) crystallographic planes and the peaks at 2θ = 22.6° and 34.7° correspond to the (002), and (023) or (004) planes, respectively. Morphological studies of commercial cotton fibers showed a length around 500-1000 μm and 25-27 μm of diameter, its have a smooth and uniform surface and show no sign of external fibrillation or formation of fibrils. Cellulose cotton whiskers provided an average length and diameter of 150 ± 50 nm and of 14 ± 5 nm, these values were calculated from the ImageJ software from about 120 counts. The size of cellulose whiskers is mainly dependent on the source and the acid hydrolysis conditions [2]. The cotton whiskers obtained showed shape similar to broader rod like and a tendency for aggregation could be observed. Acknowledgements: Capes, CNPq, Fapesp. [1] H. Zhao; J. et al. Carbohydrate Polymers, 2007, 68, 235.[2] M. A. S. A. Samir; Biomacromolecules, 2005, 6, 612.
9:00 PM - WW9.13
Quantitative Investigations of Nanoscale Elasticity of Nanofibrillar Matrices.
V. Tiryaki 1 , V. Ayres 1 , A. Khan 2 , R. Delgado-Rivera 3 , I. Ahmed 4 , S. Meiners 4
1 Electrical and Computer Engineering, Michigan State University, Lansing, Michigan, United States, 2 Department of Paper Engineering, Chemical Engineering, and Imaging, Western Michigan University, Kalamazoo, Michigan, United States, 3 Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, New Jersey, United States, 4 Department of Pharmacology, University of Medicine and Dentistry of New Jersey, Piscataway, New Jersey, United States
Show AbstractThe introduction of scaffolding materials with appropriate biochemical cues and physical properties into damaged sites within the central nervous system can encourage endogenous or exogenous cellular re-colonization. The scaffolding material currently under investigation is a synthetic electrospun polyamide nanofibrillar matrix that has demonstrated promise in tissue engineering approaches for the repair of the injured spinal cord [1] and is architecturally mimetic for the capillary basement membrane at the blood brain barrier. Recent research indicates that local elasticity can powerfully influence cellular responses [2]. For example, astrocytes possess receptor-mediated signaling mechanisms that enable these neural cells to actively probe and respond to the elasticity of their environment through exertion of strong local traction forces. Furthermore, the elasticity of native or synthetic extracellular matrix has been shown to induce differentiation of pluripotent stem cells. We present quantitative investigations of the nanofibrillar matrix elasticity, achieved through use of a dynamic new mode of atomic force microscopy, Scanning Probe Recognition Microscopy (SPRM) [3,4]. SPRM uniquely allows auto-tracking along individual nanofibers, which are then compiled into a statistical representation of the nanofibrillar matrix as a whole. Complementary transmission electron microscopy investigations are performed to assess nanofiber internal structures. Our previously published results indicate that individual nanofibers may sometimes be hollow, impacting on the elasticity of the matrix [3]. The elasticity of unmodified nanofibers and nanofibers covalently modified with fibroblast growth factor-2 (FGF-2), a prevailing cytokine involved in regulation of the growth of astrocytes, neurons, and other neural cells, are investigated. Unmodified and FGF-2 modified planar plastic surfaces serve as controls. [1] Meiners S, Ahmed I, Ponery AS, Amor N, Harris SL, Ayres V, Fan Y, Babu AN, 2007. Engineering electrospun nanofibers spinal cord repair: A discussion. Polymer Internat 56: 1340-1348. Invited manuscript for In Focus issue[2] Discher, DE, Janmey, P, Wang, YL, 2005. Tissue cells feel and respond to the stiffness of their substrate. Science, 310: 1139-1143. [3] Fan, Y, Chen, Q, Ayres, VM, Baczewski, AD, Udpa, L, Kumar, S, 2007. Scanning probe recognition microscopy investigation of tissue scaffold properties. Int. J. Nanomedicine 2: 651-661.[4] Ayres, VM, Chen, Q, Fan, Y, Flowers, DA, Meiners, SA, Ahmed, I, Delgado-Rivera, R, Scanning probe recognition microscopy investigation of neural cell prosthetic properties, in press, International Journal of Nanomanufacturing: Special Issue on Nanomanufacturing Systems, Processes and Simulation.
9:00 PM - WW9.14
Electrospun Polystyrene Buckling Coils.
Yu Xin 1 , Darrell Reneker 1
1 Polymer Science, University of Akron, Akron, Ohio, United States
Show AbstractElectrospinning offers a useful way to produce micro- and nano- polymer fibers and structures. Electrospinning utilizes an electrical force on the surface of a polymer solution or polymer melt to overcome the surface tension and produce a charged jet. This charged jet moves straight towards the grounded collector for a certain distance and bends into spiral coils. Finally the jet is solidified and collected on the grounded collector as a nonwoven cloth. The resulting fibers have complicated overlapping coiled paths[1]. The present work deals with the buckling phenomenon characteristic of a polystyrene jet. The periodic coils are attributed to the occurrence of compressive forces as the jet decelerates at the collector. Buckling-related morphologies are often accompanied by electrical bending-related morphologies. However, in this work, the fibers were collected on a moving plate before the bending instability occurred. In other words, the straight segment of the jet impinged onto the collector before the electrical bending coils formed. The buckling patterns observed include sinuous, figures-of-eight, recurring curves, coiled and other structures that resembled many patterns created by uncharged jets of highly viscous fluids impinging a hard flat surface. The resulting buckling morphologies can be controlled by changing different parameters, such as solution viscosity, conductivity, molecular weight, applied voltage, distance from spinneret to collector, atmospheric pressure, atmospheric humidity, volumetric flow rate. Besides, under certain conditions, uniformly buckled coils with nearly constant diameter can be made at a rate of one turn per microsecond. These small "springs" can be collected into durable three dimensional structures that are very soft, or as part of hierarchical structures in which the buckling loops support segments of nanofibers in a way that prevents breakage in a high velocity air stream.Reference1. T. Han, D. H. Reneker, A. L. Yarin, Polymer, 2007, 20, 6064
9:00 PM - WW9.15
Varying the Diameter of Aligned, Electrospun Fibers for Tissue Engineering Applications.
Han Bing Wang 1 2 , Michael Mullins 2 , Jared Cregg 1 , Connor McCarthy 1 , Ryan Gilbert 1
1 Biomedical Engineering, Michigan Technological University, Houghton, Michigan, United States, 2 Chemical Engineering, Michigan Technological University, Houghton, Michigan, United States
Show AbstractOne limitation in creating aligned, electrospun polymer fibers is the ability to control the fiber diameter with little variability. It is believed that by controlling the fiber diameter and the space between fibers that scaffolds can be created which differentially alter cellular migration and extension. The current study provides methods for controlling fiber diameter. The working distance (distance between the needle tip and the collection surface), the electrospinning time, and the electrospinning solvents were altered to create three groups of highly aligned, poly-L-lactic acid (PLLA) fibers for tissue engineering applications. Electrospun fibers with diameters in the micron range (1325 ± 383 nm) were created by dissolving PLLA (8 wt%) in a mixture of chloroform and dichloromethane (50:50 wt%). To create electrospun fibers with diameters in the submicron range (759 ± 179 nm), 8 wt% PLLA was dissolved into 1,1,1,3,3,3 hexafluoro-2-propanol (HFP). PLLA was dissolved into an HFP solution that contained 2 wt% of 10X phosphate buffered saline (PBS) to create nanometer diameter fibers. Also, for this situation, the working distance and collecting time was reduced, which yielded electrospun fibers with diameters in the several hundred nanometer range (293 ± 65 nm). Fiber diameter was characterized using images captured from a scanning electron microscope (SEM). To these images, the Fast Fourier Transform (FFT) and angle difference analysis were used to assess fiber alignment. The results showed that micron and submicron fibers were highly aligned. With the micron and submicron diameter fibers, 98% of the fibers were ±10 degrees of a line drawn parallel to the aligned fibers, while only 88% of the nanometer diameter fibers were ±10 degrees of a line drawn parallel to the aligned fibers. Fiber density was measured manually by counting the number of fibers per unit length (mm). The densities of micron and submicron fibers were statistically the same (600 fibers/mm) and this was accomplished by altering the electrospinning time. The density of nanometer diameter fibers (1800 fibers/mm) was three times higher than that of micron and submicron diameter fibers. By varying electrospinning parameters, unique aligned fiber geometries can be constructed to influence cellular extension and migration.
9:00 PM - WW9.16
Rheological Study of Blends of Polystyrene and Crosslinked Elastomeric PS-b-PI Copolymer Nanofiber.
Sungwon Ma 1 , Yonathan Thio 1
1 Polymer, Textile and Fiber Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractWe investigate the viscoelastic properties of blends of polystyrene and crosslinked PS-b-PI nanofibers in terms of the effect of the molecular weight, filler loading, and strain amplitude. The elastomeric block copolymer nanofiber was prepared by cold vulcanization. Varying the processing conditions allowed control of the length as well as measurement of the interaction between fiber and matrix. Rheological characterization was used to study the viscoelastic properties and filler-matrix interaction in the samples. Storage and loss moduli were found to increase with increase in filler loading in the low frequency region. We found a correlation between the molecular weight of the matrix polystyrene and the strength of matrix-fiber interaction. The Cross-Williamson model for three parameter model was used to predict and analyze zero-shear viscosity and the relaxation time. The temperature dependence of viscosity of the various blends, as characterized by the measured value of activation energy, was found to agree with expectations based on the properties of the fibers.
9:00 PM - WW9.17
Electrospinning and Microstructural Characterization of Architecturally-Discrete Isotactic-Atactic-Isotactic Triblock Stereoblock Polypropylene Thermoplastic Elastomers.
Carl Giller 1 , Giriprasath Gururajan 1 , Wei Zhang 2 , Bruce Chase 1 , Lawerence Sita 2 , John Rabolt 1
1 Materials Science and Engineering, University of Delaware, Newark, Delaware, United States, 2 Chemistry and Biochemistry, University of Maryland, College Park, Maryland, United States
Show AbstractWell-defined elastomeric stereoblock polypropylenes consisting of symmetric blocks of isotactic polypropylene covalently attached to a larger block of atactic polypropylene were recently synthesized. While the molecular weights and molecular weight distributions of the samples are comparable, the amount of total isotactic content varies for each polymer. Due to the solubility of these materials in a variety of solvents, we were able to electrospin these materials into polymeric fibers. Field emission scanning electron microscopy (FE-SEM) was employed to examine the morphology of the resultant fibrous mats as well as the diameters of the fibers. It was observed that as the percent of the isotactic content of the materials increased, the morphology of the fibers appeared less fused.Due to the unique triblock structure of these materials, it is hypothesized that the isotactic portions of each of these materials undergo different crystallization phenomena and thus possess different thermal and structural properties. Fourier transform infrared (FTIR) and Fourier transform Raman (FT-Raman) spectroscopies, as well as differential scanning calorimetry (DSC) have shown that the crystallinity of these materials increases with the isotactic content, and that electrospinning does have a realizable effect on the microstructure of these polymers. Currently we are examining these materials with small and wide angle x-ray scattering (SAXS and WAXS) in order to discern what effect electrospinning has on the long and short range order, respectively, of these materials. The SAXS measurements are being complemented by small angle neutron scattering (SANS) studies on deuterated analogues of these materials in order to discern the melting and crystallization dynamics of the selectively deuterated isotactic segments.
9:00 PM - WW9.18
Emission Color Tuning in Semiconducting Polymer Nanotubes by Energy Transfer to Luminescent Dopants.
Gareth Redmond 1
1 School of Physics, University College Dublin, Dublin Ireland
Show AbstractThe tuning of emission chromaticity in poly(N-vinylcarbazole) (PVK) nanotubes by energy transfer from the host polymer to luminescent dopants is presented. Aligned forests of close-packed nanotubes are synthesised by solution-assisted template wetting. Nanotubes typically exhibit lengths of 8-15 microns, outer tube diameter 160 nm and wall thickness 26 nm with smooth surface morphologies, few structural defects, and good dispersion of the dopants. Under optical excitation, PVK tubes display blue luminescence. By contrast, tubes doped with the organo-lanthanide chelate Eu(dbm)3(Phen), for example, exhibit well-resolved emission peaks characteristic of the europium ion with virtually no PVK emission, confirming efficient energy transfer. Emission spectra of individual doped tubes have CIE (1931) coordinates X = 0.575 and Y = 0.327 indicating good colour purity at the single nanotube level. By doping PVK nanotubes with the luminescent dyes Coumarin 6 and Nile Red, blue-green-red emission colour tuning is achieved. Tubes that are appropriately co-doped with these dyes also exhibit yellow and white emission. Exploitation of single-step Förster energy transfer to achieve shifts in emission energy in this manner is important since it allows a single material to be used as a blue light emitter, as a host for visible emitting dyes and, potentially, also as a host NIR emission dyes. This feature should simplify processing of nanotubes for multi-wavelength emissive applications.
9:00 PM - WW9.19
Manipulation, Assembly and Characterization of Optically Functional 1-D Organic Nanostructures.
Gareth Redmond 1
1 School of Physics, University College Dublin, Dublin Ireland
Show AbstractOne-dimensional (1-D) nanostructures based on organic materials are attracting significant research interest due to the many novel chemical, physical and electronic properties that may arise in highly anisotropic systems and the possibility for exploitation of such properties in a wide variety of applications. In particular, the potential of semiconducting polymer nanowires and nanotubes is now being explored for realisation of sub-wavelength photonic devices such as photodetectors, lasers and electroluminescent diodes. Successful realisation of such devices relies upon the ability to precisely manipulate and assemble these nanostructures so they can be successfully interconnected and integrated onto chips. While there has been significant research published on the assembly of inorganic nanostructures there has been very limited research carried out in relation to the assembly of organic nanostructures. To this end, we have explored a range of manipulation and assembly methods. In this talk I will present our recent results concerning nanowire manipulation and assembly by probe manipulation, magnetic fields, optical trapping, and “shear alignment”.A probe-based system was successfully developed to manipulate nanowires and assemble them into complex mesostructures for possible device applications as a step towards a nanostructure prototype test platform. AFM analysis was carried out to confirm minimal damage was done to the nanowires. Epi-fluorescence microscopic imaging indicated that the nanowires luminesced under UV excitation with intense blue light emission. Far-field fluorescence microscopy allowed for characterisation of the functionality of whole nanowires while polarized optical microscopic studies of nanowire birefringence indicated axial alignment of the polymer molecules within the wires. To magnetically manipulate organic nanowires, 30 nm Fe3O4 nanocrystals were doped into the wires and were successfully aligned when placed in an external magnetic field. A demonstration of a doped polymer nanowire as a nanoroter undergoing 360° rotation under the influence of a rotating NbFeB magnet while clocking its polarized flouresence will be presented. We will also introduce a method to successfully align random nanowire mats has been developed by drop-depositing nanowires from suspension onto a substrate where aligned nanowire arrays were achieved by the method of shear alignment. Finally, a novel optical trapping system using a Laguerre – Gaussian laser beam is introduced as a new tool for manipulation, assembly and characterization of organic nanostructures. We will demonstrate for the first time successful trapping of number of organic nanowires and nanotubes and present data concerning the nanostructures physical properties while in the beam.
9:00 PM - WW9.2
Synthesis and Characterization of Poly(2,5-benzimidazole) (ABPBI) Grafted Multi-walled Carbon Nanotube.
Ji-ye Kang 1 , Soo-mi Eo 2 , Jong-beom Baek 1
1 , Ulsan National Institute of Science and Technology, Ulsan metropolitan city Korea (the Republic of), 2 , Chungbuk national university, Cheongju Chungbuk Korea (the Republic of)
Show AbstractPolybenzobisimidazole (PBI) polybenzazoles are high performance polymers with extremely high thermal stability, mechanical properties and high chemical resistance. They have their transition temperature higher than their melting point and thus, they can be spun fibers directly from reaction mixtures. The resultant fibers display excellent textile and tactile performance. They are also used as military gadgets, fire protection gears and space materials, due to their exceptional mechanical properties and fire resistance. Among them, extensive works on PBI as fuel cell membranes have been conducted, since it has proton conductivity in broader temperature range. There are two types of monomers to prepare PBIs. The one is AA and BB monomers to yield rigid-rod or rigid coil PBIs. The other is AB monomer to afford rigid-coil ABPBI, which is the simplest among benzimidazole-type polymers. ABPBI can be prepared from inexpensive and commercially available monomer, 3,4-diaminobenzoic acid, by condensation in polyphosphoric acid (PPA). Combining ABPBI with carbon nanotubes such as muti-walled carbon nanotube (MWCNT) and single-walled carbon nanotube (SWCNT) could potentially provide various potential applications for areas, where require affordable, lightweight, multifunctional materials. In our previous study, as an approach to the preparation of ABPBI/CNT composites, in-situ polymerizations of “protonated” AB monomer were carried out in the presence MWCNT or SWCNT in a mild acidic PPA medium. It is confirmed that CNT were remained structurally intact throughout in-situ polycondensation and subsequent work-up processes. It could be concluded that the condition was indeed viable for the dispersion of CNT and polymerization of AB monomer. In addition, the purification of as-received SWCNT and in-situ preparation of composites could also be achieved in a one-pot process. In this research, SWCNT and MWCNT were functionalized with 3,4-diaminobenzoic acid via “direct” Friedel-Crafts acylation reaction in polyphosphoric acid (PPA)/phosphorous pentoxide (P2O5) to afford diamino-functionalized carbon nanotuebe (DIF-CNT). The sites are used for the grafting of ABPBI. However, the result turned out to be not only functionalization, but short-grafting occurred at the same time. Hence, ABPBI grafted CNT (ABPBI-g-CNT) were prepared via in-situ polymerization of AB monomer 3,4-diaminobenzoic acid dihydrochloride in the presence (10 wt%) of DIF-CNT such as DIF-MWCNT or DIF-SWCNT in PPA to further extend molecular weight of ABPBI grafts. During dehydrochlorination, in-situ generated hydrochloric acid, which is expected to provide additional acidity to the system, helps the dispersion and purification of CNTs as well. The resultant ABPBI-g-CNT composite films were cast from methanesulfonic acid (MSA) solution and were characterized by FT-IR spectroscopy, TGA, XRD), FESEM, FETEM, tensile properties, and electrical conductivity.
9:00 PM - WW9.20
Cell Migration on the Electrospun Fibers.
Ying Liu 1 , Alicia Franco 1 , Lei Huang 2 , Richard Clark 3 , Miriam Rafailovich 1
1 Materials Science and Engineering, SUNY at Stony Brook, Stony Brook, New York, United States, 2 Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton, New York, United States, 3 Biomedical Engineering, SUNY at Stony Brook, Stony Brook, New York, United States
Show AbstractWe have shown that en masse cell migration of fibroblasts on the planar surface results in a radial outward trajectory, and a spatially dependent velocity distribution that decreases exponentially in time towards the single cell value. If the cells are plated on the surface of aligned electropsun fibers above 1 micro in diameter, they become polarized along the fiber, expressing integrin receptors which follow closely the contours of the fibers. The velocity of the cells on the fibrous scaffold is lower than that on the planar surface, and does not depend on degree of orientation. Cells on fiber smaller than 1 micro migrate more slowly than on the planar surface, since they appear to have a large concentration of receptors. True three-dimensional migration can be observed when plating the droplet on a scaffold comprises of at least three layers. The cells still continue to migrate on the fibers surfaces, as they diffuse into the lower layers of the fibrous scaffold.
9:00 PM - WW9.21
Photocatalytic Electrospun Polymeric Nanofibers Assembled with Multilayered TiO2 Nanoparticles.
Jung Ah Lee 1 , Kevin Krogman 1 , Minglin Ma 1 , Yoon Sung Nam 2 , Paula Hammond 1 , Gregory Rutledge 1
1 Department of Chemical Engineering, MIT, Cambridge, Massachusetts, United States, 2 Department of Biological Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractThe photocatalytic degradation of toxic chemicals, including chemical warfare agents and endocrine disruptors, using TiO2 is still challenging in terms of high reaction efficiency with natural sunlight (or mild UV light), immobilization on the supporting materials, and sufficient activity without degradation of the supporting materials. In this study, we developed a potential method to prepare highly efficient photocatalytically active TiO2-coated nanofibers using Layer-by-Layer (LbL) electrostatic assembly of TiO2 and POSS (polyhedral oligosilsesquioxane) nanoparticles onto electrospun fibers at room temperature without calcination process. The TiO2-coated fibers displayed an excellent catalytic property in degradation of allyl alcohol and bisphenol A (BPA) under a mild UV illumination. We present the estrogenic activity of the BPA treated water using TiO2-coated fibers determined by assaying the proliferation of human breast cancer cell MCF-7. The methodology introduced in this paper is a facile and universal method to prepare UV stable TiO2-decorated polymer fibers to increase the reactive surface area for high efficiency of photocatalytic activity.
9:00 PM - WW9.22
Multi-scale Mechanical Analysis of Beta-solenoid Protein Structures.
Sinan Keten 1 , Jose Fernando Rodriguez Alvarado 2 , Markus Buehler 1
1 Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractBeta-solenoids are a new class of nanotube-like protein structures that are observed in virulence factors, prion proteins and amyloids. We report molecular dynamics (MD) simulation and atomistically informed continuum modeling of the nanomechanics of the beta-helix protein motif, a recently discovered protein building block forming a tube-like structure with a triangular core. We find that the beta- helix structure is extremely extensible and can sustain tensile deformation up to 800 % engineering strain without rupture of the covalently bonded protein backbone. Our atomistic simulation results reveal that the instantaneous tensile strength of the tube is proportional to the rate of H-bond rupture, providing a link between the dynamics of hydrogen bond rupture and the mechanical signature of the protein structure. This finding suggests that concurrent as opposed to sequential breaking of bonds leads to higher mechanical resistance, corroborating earlier results found in studies of beta-sheet protein domains. Inspired by the beta-helical domain of the needle-like cell puncture device of bacteriophage T4, we carry out compressive loading and bending simulations on the full atomistic structure of this domain, and show that this protein motif can withstand extremely large compressive loads, far exceeding the tensile strength of proteins. We systematically characterize the mechanical strength of this protein nanotube using molecular dynamics simulations over a wide range of deformation speeds. We illustrate that the failure strength of the molecule have power law dependence on deformation rate. We observe H-bond rupture initiation as the atomistic mechanism of instability corresponding to the peak load in the force extension curve. We show that the behavior of the protein in small compressive deformation can be approximated by a rate dependent linear elastic modulus, which can be used in context of continuum formulations for mechanical stability. Length-dependent mechanical deformation modes under compressive loading are summarized in a deformation map. Our work provides a link between the structure and functional properties of this beta-topology and illustrates a rigorous framework for bridging the gap between experimental and simulation time-scales for future compression studies on proteins. Our findings illustrate the potential of the beta-helix protein motif as an inspiration for nano-scale materials applications, ranging from stiff nanotubes to self-assembling peptide based fibers.
9:00 PM - WW9.24
The Fabrication and Dielectric Properties of Poly(vinylidene fluoride trifluoroethylene chlorofluoroethylene) Terpolymer Nanorods.
Junhong Lin 1 2 , Sheng guo Lu 2 , Minren Lin 2 , Markus Geuss 4 , Qiming Zhang 3 2 1
1 Material Science and Engineering, Penn State University, State College, Pennsylvania, United States, 2 Material Research Institute, Penn State University, State College, Pennsylvania, United States, 4 , Max-Plank Institute for Microstructure Physics , Weinberg Germany, 3 Electrical Engineering, Penn State University, State College, Pennsylvania, United States
Show AbstractPoly(vinylidene fluoride trifluoroethylene chlorofluoroethylene) (P(VDF-TrFE-CFE)) terpolymer nanorods embedded in Anodic Alumina Oxide( AAO) templates with pore sizes of 25, 70, and 200nm diameter were fabricated by extending the time of the wetting process. The instability of the wetting process induced the terpolymer infiltration into the inner space of tepolymer nanotubes, which formed mostly filled terpolymer nanorods. It was observed that all these nanorods embedded in AAO templates still possess relaxor ferroelectric behavior. The broad dielectric peak shifts progressively to higher temperatures with increasing frequency and the frequency- permittivity peak temperature fits well with the Vogel-Fulcher (V-F) relation. Moreover, the freezing temperature of the V-F relation is reduced, with the reduction of nanorod diameter. This indicates that the lateral confinement of the nanorods influences the relaxor ferroelectric behavior of the relaxor ferroelectric P(VDF-TrFE-CFE) terpolymer.
9:00 PM - WW9.25
Molecular and Mesoscale Mechanisms of Osteogenesis Imperfecta Disease.
Sebastien Uzel 1 , Gautieri Alfonso 2 , Buehler Markus 3
1 Mechanical Engineering, MIT, Cambridge, Massachusetts, United States, 2 Bioengineering, Politecnico di Milano, Milan Italy, 3 Civil Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractCollagen is a crucial structural protein material, formed through a hierarchical assembly of tropocollagen molecules, arranged in collagen fibrils that constitute the basis for larger-scale fibrils and fibers. Osteogenesis imperfecta is a genetic disorder in collagen characterized by mechanically weakened tendon, fragile bones, skeletal deformities and in severe cases prenatal death. Even though many studies have attempted to associate specific mutation types with phenotypic severity, the mechanisms by which a single point mutation influences the mechanical behavior of tissues at multiple length-scales remain unknown. Here we show by a hierarchy of full atomistic and mesoscale simulation that osteogenesis imperfecta mutations severely compromise the mechanical properties of collagenous tissues at multiple scales, from single molecules to collagen fibrils. Mutations that lead to the most severe osteogenesis imperfecta phenotype correlate with the strongest effects, leading to weakened intermolecular adhesion, increased intermolecular spacing, reduced stiffness, as well as a reduced failure strength of collagen fibrils. Our findings provide insight into the microscopic mechanisms of this disease and lead to explanations of characteristic osteogenesis imperfecta tissue features such as reduced mechanical strength and lower cross-link density. Our study explains how single point mutations can lead to catastrophic tissue failure at much larger length-scales through the activation of cascaded material failure mechanisms.
9:00 PM - WW9.27
Electrospun Composite Nanofibers for Sensor Applications.
Li Han 1 , Anthony Andrady 1 , Kim Guzan 1 , David Ensor 1
1 , RTI International, Research Triangle Park, North Carolina, United States
Show AbstractElectrospun polymer nanofiber materials have attracted tremendous interest in sensor applications as their effective sensing surface area dramatically increases with decreasing fiber diameter. The highly tunable polymer composite chemistry and surface functionality of the nanofiber material provides a wide platform for exploring different applications, such as filtration media, sound isolation materials, and sensor components. This paper presents a nanofiber sensor platform device composed of electrospun polymer/carbon composite nanofibers combined with printed electrodes directly deposited onto the surface of the electrospun fiber mat to form an integrated sensor system for detecting various chemical vapors including volatile organic compounds (VOCs) and oxidative gases. In this sensor, the composite polymer nanofibers form a chemo-resistor sensing material since the conductivity of these composite sensing materials varies with chemical vapor exposure. The sensor performance exhibits very stable baselines with dramatically reduced noise levels compared to conventional interdigitated electrodes. Furthermore, the sensor response to different vapors shows a linear relationship between conductivity change and vapor concentration in the range of ppb – ppm for some analytes, including methanol, chloroform and ozone. The sensitivity and selectivity of these sensors to different vapor analytes will also be discussed.
9:00 PM - WW9.28
Additive-induced Porosity in Electrospun PVDF Fibers.
Ying Yang 1 , Liang Chen 1 , Chia-ling Pai 1 , Miguel Amat 1 , Greg Rutledge 1 , Alan Hatton 1
1 , MIT, Cambridge, Massachusetts, United States
Show AbstractThe structure of porous fibers with diameters in the micro- to nanometer size range is of interest technologically due to the high surface area and unusual morphology they exhibit. The relationship between electrospinning parameters and morphology of such fibers is indispensable and allows for design of polymeric fibers for applications such as sensors, catalyst supports and lithium ion battery electrolyte supports. In this paper, porous fibers based on poly(vinylidene fluoride) (PVDF) are prepared by electrospinning method from dimethylformamide (DMF) in a high humidity environment. The addition of a small amount of poly(ethylene oxide) (PEO) and water to the solution of PVDF in DMF produces an unstable solution that forms a gel within several hours, but can be electrospun into fiber prior to gelation. Various morphologies such as surface porosity, interior porosity, and pores that penetrate both surface and interior of the fibers have been observed experimentally as a result of electrospinning solutions of PVDF in DMF with different additive PEO concentration, different PEO molecular weight and different non-solvent concentration, and by fabricating the fibers in controlled environments of different humidity. The final morphology is shown to depend on the ratio of drying time to phase separation time, as reported previously [Pai et al, Macromolecules 2009, 42(6), 2102]. SEM micrographs of fiber cross sections reveal that the non-solvent can induce pores within the fiber interior while the addition of PEO can enhance the phase separation on the surface of PVDF fibers. The BET surface area for PVDF fibers with both surface and interior porosity and with mean fiber diameter of 3.5±1.7 μm is around 16 m2/g; this is an order of magnitude larger than 1.7 m2/g measured for non-porous PVDF fibers with mean fiber diameter of 2.0±0.8 μm.
9:00 PM - WW9.29
Novel Conductive Biocompatible Electrospun Nanofibers for Application in Microbial Fuel Cells.
Shuiliang Chen 1 , Haoqing Hou 2 , Andreas Greiner 1
1 Department of Chemistry and Scientific Center of Materials Research, Phillips-University Marburg, Marburg Germany, 2 Jiangxi Nanofiber Engineering Center, Jiangxi Normal University, Nanchang China
Show AbstractHerein, a novel electrospun nanofibers was prepared by growing a layer of nanostructured polyaniline on electrospun polyamide nanofibers, a piece of PA electrospun nanofiber non-woven grown with nanostructured polyaniline was shown in fig 1, the green color of uniform nanofiber non-woven demonstrated that polyaniline is in the highly conductive emeraldine salt state . Polyaniline was able to be spontaneously grown onto the electrospun polyamide nanofibers through simple chemical oxidative polymerization. Polymerization of aniline is particular prone to fibrillar polymer growth.[1-3](fig 2B). The growth of polyaniline on the electrospun polyamide nanofibers make the composite fibers shown core/shell structure and very rough surface (fig2A, C). It was well known that polyaniline (PANi) is unique among the family of conducting polymer, due to the simple way of synthesis, environment stability, reversible doping/de-doping chemistry.[4] The combination of conducting polymer with electrospinning technique and the novel morphology of fiber surface, made the resulting composite nanofiber nanowoven displayed many performances, such as highly specific surface area, good conductivity, good mechanical properties, excellent bacterial compatibility and reversible hydrophilicity/ hydrophobicity. This composite nanofiber shows potential application in microbial fuel cells (MFCs), such as serving as electrode or membrane.
9:00 PM - WW9.3
Grafting of Polyaniline onto the Surface of Amino-Functionalized Multi-Walled Carbon Nanotube via Interfacial Polymerization.
In-yup Jeon 1 , Jong-Beom Baek 1
1 , Ulsan National lnstitute of Science and Technolgy, Ulsan Metropolitan city Korea (the Republic of)
Show AbstractIt is commonly known that carbon nanotubes (CNTs) show outstanding mechanical and electrical properties. A numerous CNT-based composites have been developed in the hopes of improving mechanical and/or electrical properties. Many polymers have been used as matrix materials in polymer/CNT composites for various target applications. Among these polymer/CNT composites, a few reports have focused on the covalent attachment of conducting polymers onto the surface of CNTs. Polyaniline (PANi) is unique among the family of conjugated polymers, since its doping level can be readily controlled through an acid doping and base dedoping processes. Furthermore, PANi has relatively facile processability, electrical conductivity and environmental stability. Specifically, nanostructured PANi, which is in the forms of nanorod, nanowire, and nanofiber, offers the possibility of enhanced performance due to high aspect ratio and surface area. Uniform polyaniline nanofibers were readily synthesized via interfacial polymerization without the need for templates or functional dopants. It is an effective method to suppress secondary growth of polyaniline structure, forming uniform polyaniline nanofiber. Hence, PANi grafted MWNT (PANi-g-MWNT) composite was prepared by two step reaction sequences, the functionalization of MWNT and interfacial polymerization of aniline in the presence of functionalized MWNT. First, MWNT was functionalized with 4-aminobenzoic acid in polyphosphoric acid (PPA)/phosphorous pentoxide (P2O5) medium as a “direct” Friedel-Crafts acylation reaction to yield 4-aminobenzoyl-functionalized MWNT (AF-MWNT). And then, interfacial polymerization of aniline in CH2Cl2/H2O was carried out in the presence of AF-MWNT to afford PANi-g-MWNT composites. On the basis of conventional analysis, the thermooxidative stability of dedoped PANi-g-MWNT was approximately 43centigrade higher than that of corresponding PANi. The electrical properties of PANi-g-MWNT were remarkably improved compared to those of controlled PANi. For example, the electrical conductivity of PANi-g-MWNT was approximately from 480 times to seven orders of magnitude higher than that of PANi depending upon doping state. The result should be due to PANi served as “conducting bridge” to MWNT, which have high aspect ratio and electric conductivity. In addition, the capacitance of PANi-g-MWNT composite was greatly increased compared to that of PANi as well.
9:00 PM - WW9.30
Polyethylene Oxide Nanotubes.
Woo-Sik Jang 1 , Tomonori Saito 2 , Michael Hickner 2 , Jodie Lutkenhaus 1
1 Chemical Engineering, Yale University, New Haven, Connecticut, United States, 2 Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractPolyethylene oxide (PEO) is a material widely used in drug delivery, anti-fouling coatings, polymer electrolytes, and many other applications. A significant challenge for using PEO, especially in real-world applications, is that PEO dissolves in water. Here, we report the creation of ‘all-PEO’ nanotubes with electrostatic linkages that are stable in water. We combine layer-by-layer (LbL) assembly and nanotemplating to create nanotubes of controllable diameter and length. LbL assembly, which is the sequential adsorption of cationic and anionic polyelectrolytes from aqueous solution onto a substrate, was performed on a porous anodic aluminum oxide (AAO) template. Specially synthesized PEO with cationic or anionic side groups were used as the polyelectrolytes. Here, we focus on the fabrication and characterization of PEO nanotubes which have unique physical and chemical properties. The released tubes were observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). ‘All-PEO’ LbL films were also created in a similar fashion to the tubes. Its surface morphology and thickness was observed using atomic force microscope (AFM), reflectometry, and UV-Vis spectroscopy. A water-stability test was conducted to probe the swelling response in solutions of varying ionic strength. Future work is targeted at creating coaxial nanocables using LbL assembly and nanotemplating.
9:00 PM - WW9.31
SWCNT Nanocomposites Based on an All-aromatic Liquid Crystal Poly(ether imide): Synthesis and Characterization.
Maruti Hegde 1 , Theo Dingemans 1
1 NOVAM, Faculty of Aerospace, Delft University of Technology, Delft Netherlands
Show AbstractSingle-walled Carbon Nanotubes (SWCNT) have been investigated thoroughly over the last 10 years as reinforcing nanofillers in a wide variety of polymers[1]. In an attempt to explore highly aligned polymer-SWCNT nanocomposites we are exploring uniformly dispersed SWCNTs in an all-aromatic thermotropic liquid crystalline poly (ether-imide) (PEI) matrix. The mesomorphic nature of the matrix enables the formation of highly aligned films by stretching the nanocomposites in the liquid crystalline (LC)region[2]. Dispersion by in-situ polymerisation in the presence of monomers of interest along with sonication[3] enabled the preparation of polymer nanocomposites with high SWCNT loadings (up to 8.0 vol %). Optical microscopy, Scanning Electron Microscopy (SEM) and cryo-Transmission Electron Microscopy (cryo-TEM) were employed to analyze bundle size and uniformity of dispersion in the fully imidized LC matrix at different length scales. The storage modulus increased by a factor of 2.5, i.e. from 3.2 GPa to 8 GPa and could be increased again, by a factor of more than 4, to 14 GPa for an aligned LC film at 2.5 vol% loading. A marginal increase in glass-transition temperature and thermal stability could also be observed with increasing SWCNT concentration. Mechanical properties were significantly enhanced with the incorporation of SWCNT with a maximum tensile strength increasing to 162 MPa and increase in tensile modulus to 6.0 GPa (at 2.5 vol% loading). The tensile strength and tensile modulus for the neat polymer were found to be 73 MPa and 2.5 GPa, respectively. Preliminary results have shown that the tensile strength, modulus and elongation at break can be further improved by controlling the purity of monomers and dispersion quality of SWCNT’s in the polymer matrix. An increase in conductivity of the PEI-SWCNT nanocomposite film was also recorded. The purpose of this study is to improve the mechanical and thermal properties of a high-performance PEI by incorporating well-dispersed SWCNT’s.Literature.[1] P.M. Ajayan, Chem. Rev., 1999, 99(7), 1789.[2] Dingemans T.J. et al, Macromolecules,2008, 41(7), 2474. [3] C. Park et al, Chem. Phys. Letters.,2002, 364, 303.
9:00 PM - WW9.4
Phase Structure and Conformational Change of Electrospun Poly(trimethylene terephthalate) Composite Nanofibers Containing Carbon Nanotubes.
Qian Ma 1 , Peggy Cebe 1
1 Physics, Tufts Unversity, Medford, Massachusetts, United States
Show AbstractNanofibrous composite mats were prepared by electrospinning of poly(trimethylene terephthalate), PTT, with multiwalled carbon nanotubes (PTT/MWCNT). Trifluoroacetic acid(TFA) and methylene chloride(MC) with the volume ration of 50/50 were used as the electrospining solution and is a good solvent for PTT. Scanning electron microscopy was used to investigate the morphology of electrospun (ES) nanofibers with different weight fraction of carbon nanotubes (0.2, 1%, 2% CNTs by weight respectively). Wide angle X-ray diffraction patterns from as-spun fibers were obtained. Thermal properties were determined using heat capacity measurements under standard differential scanning calorimetry (DSC) using the three-runs method for baseline correction, heat flow amplitude calibration, and sample heat capacity determination. A model comprising three phases, a mobile amorphous fraction (MAF), rigid amorphous fraction (RAF) and a crystalline fraction (C), is appropriate for PTT/MWCNT. The phase fractions, Wi (for i = RAF, MAF or C) were determined by DSC. Crystallinity increases very slightly with the amount of MWCNT loading; at the same time, a large increase in RAF was observed: WRAF of PTT fiber with 2% MWCNT is almost twice that of homopolymer PTT fiber. The addition of MWCNTs enhanced the PTT chain alignment and increase RAF as a result. The relaxation of RAF in ES PTT/MWCNT composite nanofibers was also studied. Changes of absorbance ratio corresponding to characteristic groups are obtained with the FTIR spectroscopy. The fact that the absorbance of A1358 increased while A1385 decreased with the addition of MWCNTs strongly supported the three-phase model for PTT/MWCNT.AcknowledgementsThe authors thank the National Science Foundation, Polymers Program of the Division of Materials Research, for support of this work through DMR-0602473 and the MRI Program under DMR-0520655 for thermal analysis instrumentation.
9:00 PM - WW9.5
Derivation of an Inter-fiber Potential using Molecular Simulations.
Sezen Buell 1 , Krystyn Van Vliet 1 , Greg Rutledge 2
1 Department of Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States, 2 Chemical Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractPolymer nanofibers exhibit new, emergent behavior as the diameter of the fibers is decreased from macroscopic to nanometer length scales. In particular, electrospun polymer fibers are of significant interest to several value-added applications such as biomedical scaffolds, filtration and barrier membranes, functional textiles, and flexible energy storage composites. Of fundamental necessity for many of these applications is an understanding of the mechanical performance of these electrospun nonwoven materials, which is determined by the properties of individual nanofibers, fiber orientation distributions within the nonwoven mat, and chemomechanical interactions between neighboring nanofibers during mat assembly. As many fiber-fiber junctions exist within an electrospun nonwoven mat, the interfiber interaction is especially important in determining the overall mechanical properties of this material.Here, we present our study of nanoscale fiber-fiber contacts, designed to develop an accurate understanding and representation of these fiber- fiber contacts in nonwoven mats. We use molecular dynamics (MD) and energy minimization simulations of fibers comprised of many macromolecular chains of the prototypical polymer, polyethylene (PE)represented by a united atom model; these fibers exhibit average diameters of 4.6 nm at 100 K. We briefly review our results predicting the thermal and mechanical properties of individual polymer nanofibers. We then discuss two different approaches to determine the interfiber potential, and its implementation in the characterization of nanofiber-based nonwoven mats. First, we consider equilibration of two individual fibers in a NVT ensemble, and show that the radial mass density and cross-sectional area of these fibers change significantly as a function of separation distance from 10 nm (far apart) to 2 nm overlapping. This approach indicates the absence of repulsive interactions at small interfiber separation distances. Instead, macromolecular chains from each fiber diffuse and interpenetrate the opposite fiber, which is driven by a reduction in surface energy. This results ultimately in coalescence of two fibers into a single, larger fiber. Second, we consider equilibration of two fibers via energy minimization as a function of fiber separation distance, and show that this interaction can be approximated by an interfiber interaction potential that is similar in form to Lennard-Jones. This approach indicates that repulsive interactions are sustained between fibers that interact in the absence of significant thermal energy. We discuss how each of these interfiber interaction potentials describes fiber interactions upon electrospun mat assembly and post-processing, and how these potentials relate to simulated assemblies and mechanical properties of nonwoven mats comprising hundreds of polymer nanofibers.
9:00 PM - WW9.6
Fabrication and Morphology of Nanofibers by Triaxial Electrospinning.
Yilin Liu 1 , Giriprasath Gururajan 1 , Bruce Chase 1 , John Rabolt 1
1 Materials Science and Engineering, University of Delaware, Newark , Delaware, United States
Show AbstractIn recent years, coaxial electrospinning has been used to form core/shell nanofibers. In our ongoing research on nanofiber formation, we have successfully utilized a custom-built triaxial electrospinning setup to fabricate PMMA/PEO/PMMA structure nanofibers. In the first part of our study on these complex nanofibers, the effect of changing the component contents (flow-rate and concentration) on the morphology and microstructure of the fabricated fibers will be investigated. The challenges involved in processing and characterization of these fibers will be explained. The potential applications of these triaxially spun nanofibers will also be explored.
9:00 PM - WW9.7
Photoluminescent Nanofibers for Solid-State Lighting Applications.
Lynn Davis 1 , Li Han 1 , Paul Hoertz 1 , Guzan Kim 1 , Mills Karmann 1 , Howard Walls 1 , Damaris Magnus-Aryitey 1
1 , RTI International, Research Triangle Park, North Carolina, United States
Show AbstractPhotoluminescent nanofibers (PLN) can be formed by combining electrospun polymeric nanofibers and luminescent particles such as quantum dots (QD). The physical properties of PLNs are dependent upon many different nanoscale parameters associated with the nanofiber, the luminescent particles, and their interactions. By understanding and manipulating these properties, the performance of the resulting optical structure can be tailored for desired end-use applications. For example, the quantum efficiency of quantum dots in the PLN structure depends upon multiple parameters including quantum dot chemistry, the method of forming the PLN nanocomposites, and dispersion uniformity of the quantum dot particles. This is especially important in solution-based electrospinning environments where some common solvents may have a detrimental effect on the performance of the PLN. With the proper control of these parameters, high quantum efficiencies can be readily obtained for PLNs. Achieving high quantum efficiencies is critical in applications such as solid-state lighting where PLNs may be an effective secondary conversion material for producing white light. Methods of optimizing the performance of PLNs through nanoscale manipulation of the nanofiber are discussed along with guidelines for tailoring the performance of nanofibers and quantum dots for application-specific requirements.
9:00 PM - WW9.8
Orientation Analysis for Individual Electrospun PE Nanofibers by TEM.
Taiyo Yoshioka 1 , Roland Dersch 2 , Masaki Tsuji 3 , Andreas Schaper 1
1 Material Sciences Center, Philipps University, Marburg Germany, 2 Department of Chemistry, Philipps University, Marburg Germany, 3 Institute for Chemical Research, Kyoto University, Uji Japan
Show AbstractThe electrospinning technique, which is based on the action of an electrostatic force field, involves many physical instabilities. Well known phenomena are a broad distribution of diameter, the non-uniformity of the fiber morphology, and random jet passes. Actually, the diameter and morphology of electrospun fibers have always been carefully analyzed and several theoretical approaches to clear-up the jet pass have been reported. However, there are only a few studies of the fine structure of electrospun fibers (namely orientational degree of the molecular chains, of the crystallites and of the ordered superstructures) so far by using atomic force microscopy (AFM), Raman spectroscopy, and transmission electron microscopy (TEM). Here we present a systematic analysis of the molecular orientations in single polyethylene (PE) nanofibers, mainly by selected-area electron diffraction (SAED). High temperature electrospinning of PE solution was realized using an infrared heating system along with a conventional electrospinning set-up. SAED analyses of single fibers 70nm to 1.5um in diameter clarified that the degree of crystalline orientation is strongly depending on the fiber diameter, and ranges from i) non-orientation, ii) low orientation showing the equatorial arc reflections only, and iii) high orientation showing high order reflections including meridional reflection and nearly spot like equatorial reflections. The corresponding diameter ranges are: i) > 1um, ii) 500nm - 1um, and iii) < 500nm. It is reasonable to consider that the thinner fibers were subjected to stronger bending instability and experienced the longer jet path, which leads to a stronger and more long-time action of the elongational force forming a more developed fiber structure. On the other hand, SAED analysis for beaded-fibers showed that the beads are composed of non-oriented crystals independent on the bead diameter, while the crystalline orientation of the straight parts depends on the fiber diameter. The ribbon-like fibers always showed high crystalline orientation. Structural models of the different types of fibers will be discussed. Comparing the TEM results for individual fibers with the results by XRD and DSC for fiber bundles, the importance of TEM for detailed studies of the structure of individual nanofibers is shown.
9:00 PM - WW9.9
Continuous Electrospinning Of Nylon-6 Nanofibers Using An AFM Probe Tip.
Giriprasath Gururajan 1 , Bruce Chase 1 , John Rabolt 1
1 Dept. of Materials Science and Engg., University of Delaware, Newark, Delaware, United States
Show AbstractSyringe-needle based electrospinning has been extensively explored over the years to make polymeric nanofiber mats for electronic and biomedical applications. Typically, precise control of fiber deposition and diameter, large material requirements and clogging of needles are some of its drawbacks. In this study, we have successfully utilized an atomic force microscopy (AFM) tip for electrospinning 2 wt % Nylon-6 in 1,1,1,3,3,3-hexafluoro-2-propanol. A comparison of electrospun fibers processed under similar conditions from the two techniques (syringe-needle and AFM tip) indicate significant morphological and microstructural changes for AFM tip spun fibers possibly due to the role of surface charges and electric field strength. Electrospun fibers from both techniques display the γ form crystalline polymorph. However WAXD and DSC results show a small but significant decrease in crystallinity in AFM spun fibers indicating the effect of process dynamics on crystallization kinetics.
9:00 PM - WW9:PosNanFiber
WW9.23 Transferred to WW8.10
Show Abstract9:00 PM - WW9:PosNanFiber
WW9.26 Transferred to WW8.3
Show Abstract