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
Tuesday AM, 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 Show Abstract
1 Polymer Science, University of Akron, Akron, Ohio, United States, 3 , Lanxess Corporation, Shanghai China, 2 , University of Illinois Chicago, Chicago, Illinois, United States
The 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 . 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 . 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 Show Abstract
1 , MIT, Cambridge, Massachusetts, United States
Amyloids 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 Show Abstract
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
Intermediate 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 Show Abstract
1 Mechanical Engineering and Applied Mechancis, North Dakota State University, Fargo, North Dakota, United States
Recent 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 Show Abstract
1 Chemical & Biomolecular Engineering, Cornell University, Ithaca, New York, United States
The 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.
WW2: Methods of Processing of Polymer Nanofibers I
Tuesday AM, 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 Show Abstract
1 , University of Cincinnati, Cincinnati, Ohio, United States
Electrospinning 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 Show Abstract
1 , University of Cincinnati, Cincinnati, Ohio, United States
Chemical 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 Show Abstract
1 Chemical Engineering, Cornell University, Ithaca, New York, United States
Monoaxial 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 Show Abstract
1 Electrical & Computer Engineering, University of Virginia, Charlottesville, Virginia, United States, 2 Institute of Physics, Academia Sinica, Taipei Taiwan
Polymeric 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  or electrostatic methods through insulator gaps on a conducting collector plate . 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 . 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 .References 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). Li D, Wang YL, Xia YN, “Electrospinning nanofibers as uniaxially aligned arrays and layer-by-layer stacked films”, Advanced Materials, 16, 361-366, (2004). 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). 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 Show Abstract
1 Industrial Materials Institute, National Research Council Canada, Boucherville, Quebec, Canada
The 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 . 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 .A two-step process to obtain pure PEDOT nanofibers was developed by using a combination of electrospinning and vapour-phase polymerization . 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. B. Winther-Jensen, J. Chen, K. West, G. Wallace, Macromolecules 2004, 37, 4538. A. El-Aufy, B. Naber, F.K. Ko, Polymer Preprints 2003, 44, 134. S. Nair, E. Hsiao, S.H. Kim, Chem. Mater. 2009, 21, 155. 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. A. Laforgue, L. Robitaille, Polym. Preprint 2008, 49(2), 624.
WW3: Methods of Processing of Polymer Nanofibers II
H. Young Chung
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 Show Abstract
1 Materials Science and Engineering, University of Delaware, Newark, Delaware, United States
The 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 Show Abstract
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
The 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 Show Abstract
1 , Cornell , Ithaca, New York, United States, 2 , UCLA, LA, California, United States, 3 , iFyber, LLC, Ithaca, New York, United States
Synthesis 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 . 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. 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. 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. 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 Show Abstract
1 Physics, Worcester Polytechnic Institute, Worcester, Massachusetts, United States
Abstract: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 Show Abstract
1 School of Materials Science, Japan Advanced Institute of Science and Technology, Nomi shi, Ishikawa ken, Japan
Uniaxial 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 Show Abstract
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
This 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.
4:30 PM - **WW3.7
Production Nozzle-Less Electrospinning Nanofiber Technology.
Stanislav Petrik 1 Show Abstract
1 , ELMARCO s.r.o., Liberec 9 Czechia
Theoretical 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 Show Abstract
1 School of engineering & Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
A three-dimensional (3D), highly porous substrate can mimic in vivo cell-matrix interactions more accurately than more commonly used two-dimensional substrates . 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 . 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 Show Abstract
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
A 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 Show Abstract
1 , North Carolina State University, Raleigh, North Carolina, United States
We 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 Show Abstract
1 Clean Energy Research Center, University of South Florida, Tampa, Florida, United States, 2 , Nano-RAM Technologies, Bangalore India
Syntheses 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.
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
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 Show Abstract
1 Materials Science and Engineering, University of Delaware, Newark, Delaware, United States
Although 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 Show Abstract
1 Dept. of Materials Science and Engg., University of Delaware, Newark, Delaware, United States
Real-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 Show Abstract
1 , US Army Natick Soldier Research, Development & Engineering Center, Natick, Massachusetts, United States
Confinement 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 Show Abstract
1 Physics, Tufts University, Medford, Massachusetts, United States
We 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 Show Abstract
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
Electroactive 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.
11:30 AM - **WW4.6
Electrospinning of Nanofibers - A Morphological Study.
Eyal Zussman 1 Show Abstract
1 Mechanical Engineering, Technion, Haifa Israel
In 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 Show Abstract
1 Polymer Science, University of Akron, Akron, Ohio, United States
Poly(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 Show Abstract
1 Chemical Engineering, MIT, Cambridge, Massachusetts, United States, 2 Mechanical Engineering, MIT, Cambridge, Massachusetts, United States
A 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 Show Abstract
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
Recent 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 Show Abstract
1 Corporate Technology, Donaldson Co., Inc., Minneapolis, Minnesota, United States
Electrospinning, 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
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 Show Abstract
1 Dept. of Chemistry, University of Marburg, Marburg Germany
A 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.  A. Greiner, J. H. Wendorff, Angew. Chem. Int. Ed. 2007, 46, 5670. 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 Show Abstract
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
One 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 Show Abstract
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
In 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 Show Abstract
1 Polymer, Textile and Fiber Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
The 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 Show Abstract
1 School of Materials Science and Engineering, Nanyang Technological University, Singapore, Singapore Singapore, 2 Centre of Electron Nanoscopy, DTU, Kongens Lyngby Denmark
Nanoscale 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.
4:30 PM - **WW5.6
Continuous Nano-Scaled Carbon Fibers with Superior Mechanical Strength.
Hao Fong 1 Show Abstract
1 Department of Chemistry, South Dakota School of Mines and Technology, Rapid City, South Dakota, United States
Continuous 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 Show Abstract
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
Thermal 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 Show Abstract
1 Aerospace Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
The 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 Show Abstract
1 Department of Fiber Science and Apparel Design, Cornell University, Ithaca, New York, United States
The 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.