Milo S. P. Shaffer Imperial College London
Brian L. Wardle Massachusetts Institute of Technology
Gregory M. Odegard Michigan Technological University
Jun Hyuk Moon Sogang University
Z1/Y1: Joint Session: Hierarchical Materials and Nanomaterials Integration for Photonics
Monday PM, November 29, 2010
Ballroom B, 3rd floor (Hynes)
9:30 AM - **Z1.1/Y1.1
Multiscale Periodic Polymer Composites.
Edwin Thomas 1 , Henry Koh 1 , Mary Boyce 2 , Lifeng Wang 2 , Jae-Hwang Lee 1 , Jon Singer 1 Show Abstract
1 Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States, 2 Mechanical Engineering, MIT, Cambridge, Massachusetts, United States
Polymers provide a versatile materials platform for 1, 2 and 3D periodic nano-micro scale composites with either dielectric or impedance contrast or both, and these can serve as photonic and or phononic crystals for electromagnetic and elastic waves as well as mechanical frames/trusses. Compared to electromagnetic waves, elastic waves are both less complex (longitudinal modes in fluids) and more complex (longitudinal, transverse in-plane and transverse out-of-plane modes in solids). Engineering of the dispersion relation between wave frequency w and wave vector, k enables the opening of band gaps in the density of modes and detailed shaping of w(k). Hierarchical periodic polymeric structures can be made by the bottom-up self assembly of block polymers and by top-down interference lithography and electron beam lithography. Band gaps can be opened by Bragg scattering, anti-crossing of bands and discrete shape resonances. Current interest is in our group focuses using design - modeling, fabrication and measurement of polymer based for applications as tunable optics, control of phonon flow and blast mitigation. Reference:Periodic Materials and Interference Lithography: For Photonics, Phononics and Mechanics, M. Maldovan and E.L. Thomas, (Wiley-VCH), 2009.
10:00 AM - **Z1.2/Y1.2
Stacking the Nanochemistry Deck.
Geoffrey Ozin 1 Show Abstract
1 Chemistry , University of Toronto, Toronto, Ontario, Canada
The development of active photonic crystals is a theme of great interest for a wide variety of applications. In this lecture I will address the structural and compositional diversity that is attainable in novel one dimensional photonic crystal structures known as Bragg mirrors, which can be made from a range of well known nanomaterials. The unification of various nanomaterials properties with photonic crystal structural color and active color tuning provides new chemical opportunities for the development of functional photonic structures for a myriad of perceived applications from displays to authentification devices, sensors and switches, light emitting diodes and lasers, delivery systems and catalysts.
10:30 AM - **Z1.3/Y1.3
Design and Patterning of Multiscale Functional Architectures.
Jennifer Lewis 1 Show Abstract
1 Materials Science and Engineering, University of Illinois, Urbana, Illinois, United States
The ability to pattern functional materials in planar and three-dimensional forms is of critical importance for several emerging applications, including structural scaffolds, self-healing materials, flexible electronics and photovoltaics. Direct-write assembly enables one to rapidly design and fabricate materials in arbitrary shapes without the need for expensive tooling, dies, or lithographic masks. Recent advances in the development of concentrated inks with tailored rheological properties will be highlighted with an emphasis on patterning multiscale functional architectures for these targeted applications.
11:00 AM - Z1/Y1: JointY
11:30 AM - **Z1.4/Y1.4
Plasmonic Metamaterials: From Negative-index Materials to Photovoltaics.
Albert Polman 1 Show Abstract
1 , FOM Institute AMOLF, Amsterdam Netherlands
Metamaterials are materials with artificial electromagnetic properties defined by their sub-wavelength structure rather than their chemical composition. Here, we introduce a new class of metallodielectric materials composed of a three-dimensional architecture of strongly coupled metal nanostructures embedded in a dielectric. These metamaterials posses unique properties because the metal nanostructures sustain surface plasmons, resonant oscillations of the free electrons in the metal.We will present a new plasmonic metamaterial composed of an array of strongly coupled coaxial plasmonic waveguides that shows a negative index of refraction (n=-1.0) in the UV-blue spectral range. We will show optical refraction measurements on microprisms composed of this new material structure. Negative-index materials may be used to fabricate the “perfect lens” with a resolution well below the optical diffraction limit, or to demonstrate a three-dimensional optical cloak in the visible. Integration of these novel metamaterials in optical integrated circuits will be discussed.An alternative plasmonic metamaterial, composed of an array of subwavelength plasmonic light scatterers, can be used to enhance the efficiency of thin-film solar cells. The metal nanostructures are embedded in the metal backreflector of the cell. By “folding” the light it into waveguide modes of the active semiconductor layer, light can be more efficiently absorbed, and the cell can be made significantly thinner. We demonstrate this light trapping concept using Ag nanoparticles integrated with ultra-thin amorphous Si solar cells.
12:00 PM - Z1.5/Y1.5
Modeling and Characterization of Nanostructured Photoemitters.
Vijay Narasimhan 1 2 , Samuel Rosenthal 1 2 , Daniel Riley 1 3 4 , Joel Jean 5 , Igor Bargatin 5 , Zhi-Xun Shen 1 3 4 , Yi Cui 1 2 , Nicholas Melosh 1 2 3 Show Abstract
1 Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California, United States, 2 Department of Materials Science and Engineering, Stanford University, Stanford, California, United States, 3 Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California, United States, 4 Department of Physics and Applied Physics, Stanford University, Stanford, California, United States, 5 Department of Electrical Engineering, Stanford University, Stanford, California, United States
Nanostructured materials offer multiple avenues to develop efficient photoemitters. Nanostructures on the scale of the electron diffusion length improve emission efficiency through increased electron-surface collisions. Further, light scattering from nanoscale structures can enhance absorption through anti-reflection effects and coupling to guided photonic modes. In this way, the electron escape length is decoupled from the photon absorption length in the material. However, dense, high-aspect ratio features like nanowire forests may screen electric fields, thereby reducing collection efficiencies. All of these effects depend strongly on the geometry of the structure. It is therefore essential to develop a complete, versatile set of theoretical and experimental tools to study photoemission from nanostructured cathodes.In this work, we present a suite of integrated simulation tools for designing optimized devices. We model light absorption (Fourier Modal Method/Finite Difference Techniques), carrier diffusion and recombination (Monte Carlo), and electron emission ballistics. We fabricate and characterize nanostructured photocathode materials to demonstrate some of the unique geometric effects and to validate our simulation suite. Further, we explore the use of nanostructures to enhance photoemission and photon-enhanced thermionic emission (PETE) for solar energy conversion applications.
12:15 PM - Z1.6/Y1.6
Plasmonic Enhancement of Photocatalytic Reactions.
Wenbo Hou 1 , Zuwei Liu 2 , Prathamesh Pavaskar 3 , Stephen Cronin 3 1 2 Show Abstract
1 Chemistry, University of Southern California, Los Angeles, California, United States, 2 Physics, University of Southern California, Los Angeles, California, United States, 3 Electrical Engineering, University of Southern California, Los Angeles, California, United States
Photocatalytic reactions, such as water splitting and dye decomposition, have been of great interest. While TiO2 is one of the most promising photocatalysts for this purpose, it does not absorb light in the visible region of the electromagnetic spectrum. Because of TiO2’s short wavelength cutoff, there are very few solar photons (~4%) that can be used to drive this photocatalyst. Here, we demonstrate a new mechanism for inducing increased amounts of charge in TiO2 films by exploiting the extremely large plasmon resonance of Au nanoparticles. Irradiating Au nanoparticles at their plasmon resonance frequency creates intense electric fields, which can be used to increase electron-hole pair generation in semiconductors. As a result, the photocatalytic activity of large bandgap semiconductors, like TiO2, can be extended into the visible region of the electromagnetic spectrum. By integrating strongly plasmonic Au nanoparticles with strongly catalytic TiO2, we observe a factor of 66X enhancement in the photocatalytic splitting of water and 9X enhancement in methyl orange photodecomposition under visible illumination. Electromagnetic simulations indicate that the improvement of photocatalytic activity in the visible range is caused by the enhancement of the electric field intensity near the TiO2 surface, rather than by electron transfer between the Au nanoparticles and TiO2. The intense local fields produced by the surface plasmons couple light efficiently to the surface of the TiO2. This enhancement mechanism is particularly effective because of the relatively short exciton diffusion length, which normally limits its photocatalytic activity. Our results suggest that enhancement factors many times larger than this are possible if this mechanism can be optimized.
12:30 PM - Z1.7/Y1.7
Near-ultraviolet Sensor Based on Horizontal Low Temperature Solution Grown Zinc Oxide Nanowires.
Michael Swanwick 2 1 , Sieglinde Pfaendler 2 , Akintunde Akinwande 1 , Andrew Flewitt 2 Show Abstract
2 Electrical Engineering, University of Cambridge, Cambridge United Kingdom, 1 EECS, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
A near-ultraviolet (UV) sensor based on zinc oxide (ZnO) nanowires (NWs) which is sensitive to photo excitation at or below 400nm wavelength has been fabricated and characterized. The device uses a single optical lithography step with NWs grown at low temperature from solution. ZnO is a wide direct band gap (3.37 eV) semiconductor with an absorption edge in the near-UV range, making it an ideal near-UV photodetector. Prior work on ZnO NW photodectors have been based on either high temperature furnace grown NWs or complicated 3D structure using polymer polyfluorene and PEDOT:PSS. The high temperature process limits the choice of substrate material or requires the extra processing steps of putting NWs into solution, dispersing them on a substrate, and contact formation.We report the first ZnO NW near-UV sensor that is insensitive to visible light (visible blind), fabricated using a low temperature solution process. At a voltage bias of 1V across the device, we observed a 29 fold increase in current in comparison to dark current when the NWs were photo excited by 400nm light emitting diode (LED), 8.91µA (photo excitation current) vs. 311nA (dark current). We also measured the time response of the NWs to excitation from blue to IR (470nm to 880nm wavelengths) when the device was biased at 1V. There was no response of the NW to any of the photo excitation at 470nm-880nm. When the voltage bias was increased to 5V, the device showed a small increase in current (314nm increase) at 470nm but was approximately 27 times less than the photo response to the 400nm near-UV LED (8.63µA increase) while no change was observed for green, yellow, red and IR LEDs.The fabrication of the near-UV sensor device is based on a single optical lithography step with no processing steps that exceed 100°C. A thin film of ZnO, titanium and gold are sputtered on patterned resist followed by lift-off. The sidewall of the ZnO film within the material stack acts as a seed for horizontal growth of ZnO NWs. The hydrothermal NW growth follows a well published recipe in an 80°C convection oven for 1-20hrs. The gold cap restricts vertical growth of the NWs and doubles as the device electrodes. The symmetric devices have multiple electrode shapes and gaps between the electrodes ranging from 1-20µm.The horizontally grown ZnO NWs bridge the gap between the two electrodes. The wires vary in length from 0.8 to 8.4µm and diameter from 80 to 300nm depending on growth time. The ZnO NWs either grow into each other from opposite sides or bridge the full gap depending on the electrode gap and growth time. The number of wires per device is controlled by the electrode shape and ranges from 1 NW to 1000s of NWs. The result is a self aligned ZnO NW ‘visible blind’ near-UV sensor that utilizes a low temperature process and a simple one mask optical lithography step that can be integrated on a flexible substrate.
12:45 PM - Z1.8/Y1.8
Fabrication of High Performance Transparent Silver Electrode.
Sung Kyu Kang 1 , Seon Ho Kim 1 , Youn Jun Kim 1 , Sung Yang 1 Show Abstract
1 , Kyung Hee University, Yongin Korea (the Republic of)
Recently, transparent electrodes have been received intense interest since their potential promise for in many areas including touch screen panels, flexible displays, printable electronics, OLED, OTFT, photovoltaics. Although Ag has very low resitivity, it has limited application in transparent electrode since silver electrode exhibit low transparency, which is a major disadvantage, compared with graphene- and carbon nanotube-based electrode. We have demonstrated on the fabrication of transparent Ag nanoparticle-based electrode on glass using solution process. Our self-assembly based method allows the controlled deposition of Ag nanoparticles on substrate with high transparency (> 80%) and low sheet resistance(< 40 Ω/square). Detailed atomic force microscopy (AFM) and scanning electron microscopy (SEM) reveal that the film is very uniform. The film thickness is determined to be 5 nm which is good agreement with the diameter of Ag nanoparticles.
Z2: Directed Assembly of Colloids I
Monday PM, November 29, 2010
Room 313 (Hynes)
2:30 PM - **Z2.1
Growing Colloidal Polymers from Inorganic Nanoparticles.
Kun Liu 1 , Nie Zhihong 1 , Nana Zhao 1 , Wei Li 1 , Michael Rubinstein 2 , Eugenia Kumacheva 1 Show Abstract
1 Chemistry, University of Toronto, Toronto, Ontario, Canada, 2 Chemistry, University of North Carolina, Chapel Hill, North Carolina, United States
Self-organization of nanoparticles in supracolloidal structures is an efficient approach to producing various types of nanostructures. This method remains largely qualitative, because of its inability to quantitatively predict the architectures of nanoparticle ensembles or the kinetics of their formation. We report a discovery of the striking similarity between the self-assembly of inorganic nanoparticles and reaction-controlled step-growth polymerization. The nanoparticles act as multifunctional monomer units, which form reversible, noncovalent bonds at specific bond angles and organize themselves into a 'supracolloidal' polymer. We show that the kinetics and statistics of step-growth polymerization enable a quantitative prediction of the architecture of linear, branched and cyclic self-assembled nanostructures, their aggregation numbers and size distribution, and the formation of structural isomers.
3:00 PM - Z2.2
Formation of Non-close-packed Colloidal Crystals with Template-directed Self-assembly.
Deying Xia 1 2 , Vyom Sharma 1 , Chee Cheong Wong 2 , Craig Carter 1 , Yet-Ming Chiang 1 Show Abstract
1 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 School of Materials Science and Engineering, Nanyang Technological University, Singapore Singapore
Ordered colloidal particle arrays formed with directed self-assembly have potential technological importance for catalysis, sensors, optic devices and building blocks for further fabrication. Most previous works focus on cluster of particles or close-packed particle arrays or non-close-packed patterns on colloidal-lithography defined templates. It remains a challenge to fabricate non-close-packed particle crystals addressing one particle or less at each possible template site, as well as multi-component colloidal crystals. We developed a facile approach to fabrication of 1D and 2D non-close-packed colloidal crystals on nanolithography defined templates. Colloidal particles were deposited to form non-close-packed patterns using convective deposition. The non-close-packed particle chain was formed on the groove while the patterns with alternatively filling one hole with one colloidal particle and keeping one or two holes empty were successfully obtained on 2D square or hexagonal templates of holes. Furthermore, the multi-component colloidal crystals were fabricated on 2D templates with subsequent deposition of other kinds of particles. Finally, the diamond structure could be fabricated with further fabrication and selective removal of one type of particle as initial demonstration for application in photonic crystals.
3:15 PM - Z2.3
Hierarchical Structure Fabrication by Evaporative Self Assembly of Nanoparticles on Microstructures.
Hyuk-Min Kwon 1 , Adam Paxson 1 , Kripa Varanasi 1 Show Abstract
1 Department of Mechanical Engineeirng, M.I.T., Cambridge, Massachusetts, United States
Ordered three-dimensional micro/nano hierarchical surface textures can provide benefits to many applications, including inherent wettability enhancement and photonic crystal fabrication. We present a simple method for manufacturing well-defined micro/nano hierarchical structures based on self-assembly of colloidal nanoparticles around lithographically patterned micro-pillars. Different sizes of silica nano particles are self-assembled from colloids on different designs of micro-pillar forests. We found that simple spin-coating of colloidal nano particles on micro pillars creates regularly repeatable nanoparticle aggregations, and micro-pillar structure design plays a key role in the final shape of self-assembly patterns of nanoparticles. There are three different regimes of self-assembled patterns along different spacing ratios as well as aspect ratios of micro-pillar design. Our mathematical model of meniscus shapes of nanoparticle colloids between micro–pillars predicts the different shapes of self-assembled nanoparticle patterns. This approach provides a pathway for ordered, low-cost, scalable manufacturing techniques of hierarchical structures.
3:30 PM - Z2.4
Formation of Three-dimensional Colloidal Nanoparticle Superlattices in Spatially Controlled Locations and Probing the Formation Mechanism.
Chenguang Lu 1 , Austin Akey 1 , Irving Herman 1 Show Abstract
1 Applied Physics and Applied Mathematics, Columbia Univeristy, New York, New York, United States
A multiple solvent system consisting of colloidal nanoparticles in several solvents of gradually decreasing vapor pressures was investigated in the self assembly of hundred-layer thick colloidal nanoparticle superlattices in lithographically defined capillaries. Such a solvent system allows a very slow and tunable drying rate of solvents, which, together with the microfluidic flow into the capillaries, leads to the controllable formation of large, single crystalline 3D nanoparticle supercrystals. The underlying mechanism of superlattice formation was investigated via the drying rates for nanoparticle assembly for solvent systems of specific compositions. This technique generates single-crystalline 3D supercrystals of ~micrometer size at spatially controlled locations. The ordered nature of the structures formed was probed by high-resolution SEM and small angle x-ray scattering. This technique is versatile and has been applied to various types and sizes of colloidal nanocrystals, including those composed of CdSe and FexO.
3:45 PM - Z2.5
Facile Fabrication Routes for Viral Synthetic Hybrid Microparticles.
Christina Lewis 1 , Wui Siew Tan 2 , Daniel Pregibon 2 , Yan Lin 1 , Cuixian Yang 1 , Amy Manocchi 1 , Nicholas Horelik 1 , Kai Yuet 2 , Patrick Doyle 2 , Hyunmin Yi 1 Show Abstract
1 Chemical and Biological Engineering, Tufts University, Arlington, Massachusetts, United States, 2 Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
We present two facile fabrication routes for viral synthetic hybrid microparticles. In the first route, we hierarchically assemble genetically modified tobacco mosaic virus (TMV) nanotemplates with encoded polymeric hydrogel microparticles via nucleic acid hybridization. The encoded microparticles are produced in a high throughput microfluidic device via stop-flow lithography (SFL), and consist of spatially discrete regions containing encoded identity information, an internal control, and capture DNAs. For the hybridization based assembly, partially disassembled TMVs are programmed with linker DNAs that contain sequences complementary to both the virus 5’end and a selected capture DNA. Fluorescence microscopy, atomic force microscopy (AFM), and confocal microscopy results clearly indicate facile assembly of TMV nanotemplates onto microparticles with high spatial and sequence selectivity. In the second route, we directly embed functionalized viral nanotemplates in polymeric hydrogels. Specifically, genetically modified TMV nanotemplates are covalently labeled with fluorescent markers or metalized with palladium (Pd) nanoparticles (Pd-TMV), then suspended in a poly(ethylene glycol)-based solution. Upon formation in a microfluidic flow-focusing device, droplets are photopolymerized with UV light to form microparticles. Fluorescence and confocal microscopy images of microparticles containing fluorescently labeled TMV show uniform distribution throughout the microparticles. Catalytic activity, via the dichromate reduction reaction, is also demonstrated with microparticles containing Pd-TMV complexes. Additionally, Janus microparticles are fabricated containing viruses embedded in one side and magnetic nanoparticles in the other, enabling simple separation from bulk solution. This fabrication route harnesses the advantages of viral nanotemplates in a readily usable and stable 3D assembled format. Overall, both routes demonstrated in this presentation exploit exquisite multifuntionality of viral templates and rapid microfluidic fabrication of monodisperse hydrogel microparticles. We envision that the assembly methods and the hybrid microparticles could be readily deployed in a wide range of applications such as biosensing or catalysis, where readily assessable functionalities from nanomaterials are highly desired.
4:00 PM - Z2.6
Energy Landscapes and Defects in Self-assembly with Precisely Patterned Polyhedral Units.
Jatinder Randhawa 1 , Levi Kanu 1 , Gursimranbir Singh 1 , David Gracias 1 Show Abstract
1 Department of Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, Maryland, United States
To date, most hierarchical non-molecular assemblies have utilized very simplistic building blocks such as spheres, with little to no surface patterning. We describe self-assembly of three dimensional structures using polyhedral units (tetrahedra, cubes) with precise hydrophobic surface patterns. The polyhedral nature of the unit results in previously unrealized hierarchical aggregates, whereas precise surface patterns control docking and enable assembly with minimal defects. Additionally precise patterns can enable novel optical functionality. We will describe a study that systematically investigates the effect of surface patterning on defect mitigation in three dimensional self-assembly. Here, we utilized precisely patterned hydrophobic self-assembling polyhedral units. We utilized energy landscape calculations and experiments to study the type of defects that arise based on the geometric design of the pattern. The total area of the pattern defines the global energy minima on the energy landscape, however, we found that by altering the distribution of the area, we can minimize defects. For the same overall area, the defects in the self-assembled aggregates can be mitigated by minimizing the radius of gyration and maximizing the angular distribution of the surface pattern. We experimentally realized self-assembled structures with two patterns chosen based on energy calculations, one of which provides fewer defects as compared to the other surface pattern. The theoretical findings based on the parameters derived from energy landscape calculations strongly correlate with the experimental results thereby enabling easily computable design rules for high fidelity three-dimensional self-assembly. J. S. Randhawa, L. N. Kanu, G. Singh and D. H. Gracias. “The importance of surface patterns for defect mitigation in self-assembly” Langmuir (2010) accepted.
4:15 PM - Z2: Colloids I
Z3: Multiscale Carbon Nanotube Composites I
Monday PM, November 29, 2010
Room 313 (Hynes)
4:30 PM - **Z3.1
Multifunctional Carbon Nanotube Composites.
David Lashmore 1 , Brian White 1 , Mark Schauer 1 , Chlesea Brennan 1 , Meghann White 1 , Cory Timoney 1 Show Abstract
1 R&D, Nanocomp, Concord, New Hampshire, United States
Macroscale composites fabricated from carbon nanotube sheets can exhibit a variety of useful concurrent properties. Examples include: (1) very high strength/stiffness and high EMI/EHD shielding, (2) very low thermal conductivity and very high electrical conductivity, and (3) very good electrical conductivity at moderate to high frequency and very light weight.Nanotube containing composites have traditionally been synthesized by dispersion of loose CNT’s into a liquid matrix. We describe an alternative process taking advantage of capillary forces to create fully dense macroscale CNT composites of over 50% loading with consequent improvements in properties. This type of process can even take place on commercial prepregging machines. The challenge in all CNT based composites is to take advantage of the extraordinary properties of the individual 1nm diameter nanotubes that may be as short as 1 mm, in a composite that may contain vary large numbers of tubes joined only by weak forces. Among the properties of interested are the ballistic properties, strength and modulus, and electrical properties. We have measured strength values near 3 GPa with modulus values of 110 GPa. The EHD behavior of these materials has been sufficient so that they are now being used for this purpose on at least one satellite. Their thermal conductivity decreases with temperature ranging from a maximum of 100 W/m K to at low temperature around 2 W/m K. When sheets of CNT material are stacked with ceramic spacers they exhibit thermal conductivity normal to the plane of less than 0.02 W/m K. This is aerogel like behavior but comes with very good electrical conductivity in plane, high strength, flexibility even at very low temperatures, and extreme impact resistance. The electrical conductivity varies with frequency, and the absence of the skin effect and internal capacitive coupling provides a material that only gets better as the frequency increases.
5:00 PM - Z3.2
Assembly of Carbon Nanotubes in Highly Organized Architectures.
Mei Zhang 1 2 Show Abstract
1 Industrial and Manufacturing Engineering, FAMU-FSU College of Engineering, Tallahassee, Florida, United States, 2 High-Performance Materials Institute, Florida State University, Tallahassee, Florida, United States
Carbon nanotube (CNT) is a one dimensional molecule formed by benzene rings. Their excellent electrical, thermal, and mechanical properties make them useful materials for broad applications. To realize CNTs remarkable properties in the applications, it is required to assemble CNTs into highly organized structures, such as array, sheet, and yarn as well as the higher level architectures. In this work, we developed the processes to assemble CNTs into specific sheets and yarns. Based on the CNT sheets, we further fabricated highly organized architectures which involve cardboard and honeycomb structures. These structures can efficiently utilize the marvelous properties of CNTs and make them available into real world applications.
5:15 PM - Z3.3
Forces in a Model for Solid-state Fabrication of Macroscopic Sheets and Yarns from Nanoscopic Carbon Nanotubes.
Alexander Kuznetsov 1 , Alexandre Fonseca 2 , Ray Baughman 1 , Anvar Zakhidov 1 Show Abstract
1 Alan G. MacDiarmid NanoTech Institute, University of Texas at Dallas, Richardson, Texas, United States, 2 Departamento de Física, Instituto de Ciências Exatas (ICEx), Universidade Federal Fluminense, Volta Redonda, Rio de Janeiro, Brazil
The forces describing the mechanism of the dry-drawing process of fabrication of macroscopic sheets and yarns are presented based on a model developed by us for the conversion of vertically oriented carbon multiwall nanotube (MWNT) forest to a horizontally oriented MWNT sheet or yarn. The model for the carbon nanotube (CNT) forest consists of vertically aligned large bundles of nanotubes interconnected by individual CNTs or small bundles. The two principal processes involved in our proposed self-assembly mechanism for MWNT sheet formation are: 1) un-zipping after bending of the interconnections leading to their peeling-off between CNT big bundles in the forest and 2) self-strengthening of these interconnects at the top and bottom of the forest during draw-induced reorientation of the CNT bundles. In this presentation, we focused on the description of the forces between interconnects and CNT big bundles during the solid-state draw. Dynamic SEM imaging and other experimental results will be presented in support of our model.
5:30 PM - **Z3.4
Assembly Strategies for Fully Aligned and and Dispersed Morphology Controlled Carbon Nanotube Reinforced Composites Grown in Net-shape.
Benjamin Farmer 1 , Mark Beard 2 , Oana Ghita 2 , Robert Allen 2 , Daniel Johns 3 , Ken Evans 2 Show Abstract
1 , Airbus Operations Ltd., Bristol United Kingdom, 2 School of Engineering, Mathematics and Physical Science, University of Exeter, Exeter United Kingdom, 3 , EADS UK Ltd, Bristol United Kingdom
Long carbon fibre polymer composites represent the state-of-the-art materials technology for high performance weight driven structures, such as airframes. Although a significant amount of optimisation remains to be done to fully exploit the benefits of long fibre composites, these materials are relatively speaking still very crude, when compared to what nature has achieved with wood or bone for example. Nanomaterials, and specifically carbon nanotubes (CNTs), have teased with their spectacular mechanical and physical properties in isolation. These headline properties have prompted much work into the manufacturing of composite materials using CNTs as a reinforcement, but thus far, successful exploitation of these impressive properties has been modest. A gap remains before these materials represent a real competition to long carbon fibre composites, even though fairly modest applications such as CNTs as fillers for matrix toughening and imparting electrical functionality are showing some promise. In this paper a critique is made of various reinforcement approaches through the lens of ‘nano-augmented’, ‘nano-engineered’ and ‘nano-enabled’ categories as defined by Airbus. These approaches are compared to an analysis of nature’s ‘baseline’. A new ‘nano-enabled’ strategy; for the growth of fully aligned and dispersed bulk carbon nanotube composite materials and structures, allowing for simultaneous multi-scalar morphological and topological optimisation, is described. This new strategy, analogous to nature’s approach, consists of the vapour phase growth of aligned forests of carbon nanotubes coupled to the environment of Additive Layer Manufacturing (ALM). Early feasibility results are presented and currently identified challenges to successful scale-up are discussed.
Z4: Poster Session: Mesoscale Hierarchical Materials
Tuesday AM, November 30, 2010
Exhibition Hall D (Hynes)
9:00 PM - Z4.1
Formation of Micro and Nanostructured Nickel/Silica and Nickel/Metal Composites by Electrodeposition of Mesoporous Silica onto Nickel Foam.
Nikolas Cordes 2 , Martin Bakker 2 1 Show Abstract
2 Chemistry, The University of Alabama, Tuscaloosa, Alabama, United States, 1 Center for Materials for Information Technology, The University of Alabama, Tuscaloosa, Alabama, United States
Porous electrodes are of interest in areas ranging from supercapacitors and advanced batteries to electrocatalysis. These applications all require high surface area and bicontinuous porousity. Surfactant and polymer templated sol-gel mesoporous silicas are a widely used method to produce high surface area thin films and particles. By using electrodeposition we have been able to coat nickel foam with highly adherent thin films of mesoporous silica templated by cationic surfactants. Removal of the surfactant template leaves a porous coating that can be used as a template for electrodeposition of metal nanostructures. If the electrodeposition of the mesoporous silica is continued for periods exceeding ca. 15 minutes mesoporous silica particles are formed which are loosely adherent to the nickel foam surface. Chemical processing of these films improves the binding of the mesoporous silica particles. The resulting thick films can essentially film the pores in the nickel foam and be used as a template for electrodeposition of microstructured metals.
9:00 PM - Z4.10
Decontamination of Large Alkyl Halides Using a Mesoporous NaX Zeolite.
Min-Hong Lee 1 , David Doetschman 1 , Qing-Guo Meng 1 , Charles Kanyi 1 , Jurgen Schulte 1 Show Abstract
1 Chemistry Department, SUNY Binghamton University, Binghamton, New York, United States
Many studies show the effectiveness of NaX, as a nucleophilic reagent, toward decontamination of various hazardous substances. From our group’s previous studies, the decontamination of alkyl halide by NaX was found to be successful. In this study, a mesoporous NaX (Meso-NaX) is synthesized using polymer precursor to decontaminate various large alkyl halides. The Meso-NaX’s reactivity toward alkyl halide will be discussed along with unique characteristics of synthesized Meso-NaX. A change in overall yield of alkylation by use of Meso-NaX will be covered. Lastly, the effect of subsequent addition of water on the reactivity of Meso-NaX zeolite will be discussed.
9:00 PM - Z4.13
Mesoporous Zirconia Thin Films with 3-Dimensional Mesostructures and Their Application to pH-Switchable Membranes.
Young-Seon Ko 1 , Ki-Rim Lee 1 , Ji-Hoon Jang 1 , Young-Uk Kwon 1 2 Show Abstract
1 Chemistry, Sungkyunkwan University, Suwon Korea (the Republic of), 2 SKKU Advanced Institute of Nanotechnology, Sungkyunkwan university, Suwon Korea (the Republic of)
We synthesized mesoporous zirconia thin films (MZTFs) by using a mixed solution in which zirconium hydroxide nanoparticles were self-assembled with amphiphilic block copolymers (ABCs). Those sol nanoparticles were prepared by refluxing ZrOCl28H2O and concentrated HCl in ethanol, and then characterized by dynamic light scattering, X-ray diffraction, and energy-dispersive X-ray spectrometry. These characterizations revealed that the sol nanoparticles were zirconium hydroxide with a hydrodynamic diameter in the range of 9−12 nm. To synthesize non-silica mesoporous materials, not only the self-assembly properties of ABCs as templates but also the condensation reactions of inorganic species should be controlled. The self-assembly of ABCs can be controlled quite easily through thermodynamics. In contrast, the behavior of inorganic species depends on kinetic factors, so that controlling the kinetics is more difficult and complex. The prehydrolyzed zirconium hydroxide nanoparticles play an important role in reducing the kinetic factors during the formation of a mesostructure.1 Consequently, we could synthesize MZTFs with highly ordered and 3-dimensional mesostructures as confirmed by small-angle X-ray scattering, scanning electron microscopy, and transmittion electron microscopy. Because the 3-dimentional mesostructures have accessible pores to conducting substrates, these mesostructures are very suitable to apply to a wide variety of membranes. For a pH-switchable membrane, we utilized cyclic voltammetry with Fe(CN)63− ions as electroactive probes by varying the value of pH. The charge of zirconia surface is changed with the value of pH of the solution, so that our MZTFs allow the Fe(CN)63− ions to pass through their framework when the surface is charged positively. Furthermore, zirconia is stable in strong basic solution, whereas silica, which is used frequently as the material of membranes, is readily dissolved in such a solution. We thus expect that our MZTFs can be applied to the pH-switchable membrane under a wide range of pH values compared with mesoporous silica films.2,31. Hwang, Y. K.; Lee, K.-C.; Kwon, Y.-U. Chem. Commun. 2001, 1738.2. Etienne, M.; Quach, A.; Grosso, D.; Nicole, L.; Sanchez, C.; Walcarius, A. Chem. Mater. 2007, 19, 844.3. Fattakhova-Rohlfing, D.; Wark, M.; Rathouský, J. Chem. Mater. 2007, 19, 1640.
9:00 PM - Z4.14
Mesoporous Silicate Films with Tunable-size and Shape Channels Templated from Polystyrene-b-Poly(tert-butyl acrylate) by Supercritical Fluid Infusion.
Li Yao 1 , John Ell 1 , James Watkins 1 Show Abstract
1 Department of Polymer Science and Engineering, University of Massachusetts Amherst, Amherst, Massachusetts, United States
Mesoporous metal oxide films with patterned morphology at the nano and micro scales have a lot of applications in microelectronics, microfluidics, sensors, catalysis and photovoltaic. We use chemically amplified block copolymers as templates in supercritical fluids to fabricate mesoporous silicate films with direct dual-tone patterning. The block copolymer (BCP) that will be utilized in this endeavor is poly(styrene-b-tert-butyl acrylate) (PS-b-PtBA). A photo acid generator can generate acid upon exposure to UV light to deprotect PtBA to Poly acrylic acid (PAA) through the chemical amplication. This acid generation also plays an important role in catalyzing the silica precursor, tetraethylorthosilicate (TEOS), to condense within the PAA domain. The deprotection and silica condensation should happen at the same time within the supercritical CO2 reactor at a certain temperature and pressure.The phase separated block copolymer template is the key to the morphology and size within the silicate film. While Flory parameter, χ, is important for the segregation strength, the volume fraction (f) of each block determines the morphology and degree of polymerization (N) determines the domain size.Atomic transfer radical polymerization (ATRP) was used to synthesize a series of PS-b-PtBA block copolymers with different volume fractions and molecular weights. The morphology of the block copolymers were achieved through solvent annealing. Once the desired morphology and domain size was reached, supercritical fluid infusion followed by a high temperature calcination step proceeded to yield a mesoporous silicate film for each of the polymer templates of interest. Three kinds of mesoporous silicate films have been fabricated with spherical pores, cylindrical channels, and bicontinuous channels templated from PS-b-PtBA films with spherical, cylindrical and gyroid morphologies respectively in different period length (20-80 nm). Transmission electron microscopy (TEM) was conducted to characterize the structure of those mesoporous silicate films. X-ray Scattering (GISAXS/2-D SAXS) measurements were also used to assign the ordered morphologies, d space value and the orientation of the ordering. The alignment of cylindrical channels within the mesoporous silica films is studied by varying the solvent annealing conditions and substrate effects for the pre-ordering of the polymer template. And the application of those mesoporous silicate films is also under investigation. Reference:  Nagarajan, S.; Russell, T.P.; Watkins, J.J. Adv. Funct. Mater., 2009, 19, 2728. Bates, F.S. Science, 1991, 251, 898. Davis, K.A.; Charleux, B.; Matyjaszewsk, K. J. Polymer Sci. Polymer Chem., 2000, 38, 2274.
9:00 PM - Z4.15
The Adsorption of Organophosphates into Microporous and Mesoporous NaX Zeolites and Subsequent Chemistry.
Qingguo Meng 1 , David Doetschman 1 , Charles Kanyi 1 , Min-Hong Lee 1 , Jurgen Schulte 1 Show Abstract
1 Chemistry, State University of New York, Binghamton University, Binghamton, New York, United States
Adsorption and decontamination of Organophosphates (OPs) into microporous and mesoporous aluminosilicate zeolite with minimal environmental impact was performed under mild circumstances. Micro sized sodium zeolite X (NaX), low silicate zeolite X (LSX) and cationic polymer (polydiallyl dimethyl ammonium chloride, PDADMAC) templated mesoporous NaX with short and long polymer chain lengths, which leading to different sizes of mesopores, were used as the adsorptive solids. The nucleophilic chemistry of trimethyl phosphate (TMP) and tripropyl phosphate (TPP), which were selected as the OPs examples, was investigated after their absorption into the pores of different zeolites. Stoichiometric amount of water was also introduced into the OPs exposed zeolite and hydrolysis was observed. The textural properties of the obtained zeolites were characterized by X-ray different (XRD) and nitrogen adsorption/desorption. The OPs exposed zeolites before and after water addition were characterized by solid state 31P and 13C CP MAS NMR. The analysis of washing solution from OPs adsorbed zeolites by solution 1H, 13C and 31P NMR confirmed the catalytic products and the mechanism was proposed correspondingly. The experimental results indicates that the TMP undergoes almost identical decontamination in both microporous and mesoporous NaX, while TPP, which has much larger molecule size, presents better catalytic property in mesoporous NaX than that in microporous NaX, due to the possible size limitation.
9:00 PM - Z4.16
Formation of Porous Silver, Nickel and Cobalt Monoliths by Solution Infiltration into Porous Silica Monoliths.
Franchessa Maddox Sayler 2 , Amy Grano 2 , Martin Bakker 2 1 , Jan-Henrik Smatt 3 , Mika Linden 3 Show Abstract
2 Chemistry, The University of Alabama, Tuscaloosa, Alabama, United States, 1 Center for Materials for Information Technology, The University of Alabama, Tuscaloosa, Alabama, United States, 3 Physical Chemistry, Abo Akademi University, Turku Finland
By using sol-gel processing incorporating a polymer and cationic surfactant as templates, porous silica with porosity at nanometer and micrometer length scales has been formed. It is possible to form samples of relatively large dimensions (up to10 cm), although shrinkage during processing is such that it is difficult to produce pieces of a predetermined size. Solutions of metal salts, particularly metal nitrates, were introduced into the porous silica, dried and heated to decompose the metal salt to the metal oxide. For silver salts heating reduces the salt to metallic silver. In the case of nickel and cobalt reduction under hydrogen is necessary to produce the corresponding metal. An hydroxide etch removes the silica leaving porous silver, nickel and cobalt. If carried out under appropriate conditions after etching the metal is one, bicontinuous piece. SEM characterization shows the metal monoliths to be porous at three lengths scales: 2-5 micrometers due to the polymer, 50-300 nanometers due the formation of mesoporous silica particles during the sol-gel processing, and 5-10 nanometers due to the presence of the cationic surfactant template. By varying the concentration of the metal nitrate, the processing temperature, and the number of times the metal salt was added to the porous silica, the nature and extent of the porosity can be controlled. The surface areas of these materials was studied by nitrogen gas adsorption, and was found to be as high as 80 m2/g.
9:00 PM - Z4.17
Solvothermal Synthesis of Highly Hierarchical Urchin-like LiFePO4 Mesocrystals and LiFePO4/C Composites.
Jelena Popovic 1 , Markus Antonietti 1 , Maria-Magdalena Titirici 1 Show Abstract
1 Colloids, Max Planck Institute of Colloids and Interfaces, Potsdam Germany
Mesocrystals as described by Cölfen et al.  are 3D ordered nanoparticle superstructures with new chemical and physical properties rising from their unique hierarchical mesostructure. Consequently, mesocrystals have a high potential for many applications, such as sensors, catalysts, solar cells and in particular high rate electrode materials due to their highly porous structure consisting of interconnected nanocrystals. Since its discovery by Padhi et. al. , olivine lithium iron phosphate has been highlighted as one of the most promising cathode material for large size Li-ion batteries due to its high stability, high power and low cost. Until recently, morphosynthesis of LiFePO4 mesocrystals or its crystal assemblies have been scarcely reported due to its multielement nature. In this work, we report simple a one-step, template-free, low temperature solvothermal route for synthesis of hierarchically structured LiFePO4 with and without carbon coating. Scanning electron microscopy (SEM) of the obtained materials showed uniform and dispersed urchin-like mesocrystals with diameter of 20 μm. Mesocrystals were formed by the arrangement of primary plate units in a manner very similar to the earth magnet model. Further studies (High-resolution transmission electron microscopy and X-ray diffraction) revealed high puritiy and crystallinity of synthesized materials with a thin amorphous layer (~2nm) on the surface of the crystallites in the case of the carbon containing composites. Furthermore, it was found by a series of experiments that this strategy enables tailoring of morphology and purity of LiFePO4 mesocrystals in dependence of the iron precursor, reaction time and concentration of the starting reaction solution. We are currently studying the electrochemical performance of these materials.  Cölfen H, Antonietti M, Mesocrystals: Inorganic Superstructures Made by Highly Parallel Crystallization and Controlled Alignment, Angew. Chem., Int. Ed. 2005; 44(35):5576-5591;  Padhi, AK., Nanjundaswamy KS, Goodenough JB, Phospho-olivines as Positive-Electrode for Rechargeable Lithium Batteries. J. Electrochem. Soc. 1997
9:00 PM - Z4.18
Modeling Material Properties of Freestanding Nanoparticle Membranes.
Henry Chan 1 , Alexey Titov 1 , Lela Vukovic 1 , Jinbo He 2 , Petr Kral 1 , Heinrich Jaeger 2 Show Abstract
1 Chemistry, Uinversity of Illinois at Chicago, Chicago, Illinois, United States, 2 Physics, Uinversity of Chicago, Chicago, Illinois, United States
Recently, freestanding membranes of ligated nanoparticles have been prepared and investigated . We use atomistic and coarse-grained molecular dynamics simulations to model the stability, mechanical properties, molecular permeability, and molecular storage capability of these membranes. We show how these parameters depend on the particle size, composition, ligand type, and number of particle monolayers . We also discuss the self-assembly of ligated nanoparticles, nanorods, and nanodiscs in the interior of the hydrated phospholipid membranes . Bigioni, T. P.; Lin, X.-M.; Nguyen, T. T.; Corwin, E. I.; Witten, T. A.; Jaeger, H. M., Nat. Mater., 2006, 5(4), 265-270 Chan, Henry; Kral, Petr (in preparation) Titov, Alexey; Chan, Henry; Kral, Petr (in preparation)
9:00 PM - Z4.19
Templating with Silver Nanoparticle Morphologies: Gold plating, Shells, and Frames.
Matthew McEachran 1 , Vladimir Kitaev 1 Show Abstract
1 Chemistry, Wilfrid Laurier University, Waterloo, Ontario, Canada
Silver nanoparticles (AgNPs) are advantageous for a plethora of applications due to the synthetic ability to efficiently control their sizes and shapes, combined with advanced optical and electronic properties. The AgNPs that we have produced and investigated include decahedra , pentagonal rods , prisms  and cubes/bi-pyramids . Ag has multiple advantages in terms of shape selection due to its optimal reactivity but has limitations when it comes to stability. To overcome the limited stability in silver, gold has been demonstrated by Xia  to effectively replace Ag, conserving the original AgNP shape. Au is more chemically stable than silver, but has limited shape selection, therefore Au replacement is exploited as a means to aid in stability and shape selection, thus overall amplifying Ag and Au advantages and eliminating shortcomings. Au deposition can be performed according to three scenarios; (i) shell, (ii) frame and (iii) plating formation dependent on the amount of Au, replacement time and presence of reducing and etching agents. (i) Shell formation occurs when galvanic replacement of the AgNP occurs leaving a hollow core and an Au shell. (ii) Frame formation is the deposition of Au along the polyhedral edges leaving the body hollow. (iii) Plating is the formation of a thin layer of Au around the AgNP while maintaining the Ag core intact. Each scenario has unique properties that can be exploited in various applications, (i) shells in clinical diagnostics and treatment ; (ii) frames in surfaced enhanced Raman (SERS) , and (iii) plating in optics and electronics . With Au shells improved stability in contrast to their Ag precursors this makes them attractive for the formation of silica shells. Silica shells have been formed with tetraethyl orthosilicate (TEOS) in basic conditions. Formation of well-defined metallodielectric composites particles and their ordered self-assembled array is the current focus of our research. This presentation will discuss morphological transformations for each scenario; shell, frame and plating, and self-assembly of these functional building blocks to highly-ordered composite materials. Pietrobon, B.; Kitaev, V. Chem. Mater. 2008, 20, 5186-5190.  Pietrobon,B.; McEachran, M.; Kitaev, V. Acs. Nano 2009, 1, 21-26. Cathcart, N.; Frank, A.; Kitaev, V. Chem. Commun. 2009, 7170-7172 McEachran, M; Kitaev, V.. Chem. Commun. 2008, 5737-5739 Sun, Y.; Mayers, B. T.; Xia, Y. Nano Lett. 2002, 2, 481. Sun, Y.; Xia, Y. Science, 2002, 298, 2176 Skrabalak, S.; Chen, J.; Au, L.;, Lu, X.; Li, X.; Xia, Y. Adv. Mater., 2007, 19, 3177 Shipway, A..; Katz, E.; Willner, I. Chem. Phys. Chem. 2000, 1, 18–52.
9:00 PM - Z4.2
Nanostructured Carbohydrate-derived Carbonaceous Materials.
Shiori Kubo 1 , Robin White 1 , Markus Antonietti 1 , Maria-Magdalena Titirici 1 Show Abstract
1 Colloid department, Max Planck Institute of Colloids and Interfaces, Potsdam-Golm Germany
We report on the production of carbonaceous materials with ordered pore structures and oxygenated surface functional groups using the hydrothermal carbonisation of carbohydrates. The method exploits the templating of block copolymer micelles within a carbon matrix in an aqueous environment. The nanostructured carbon materials were synthesised by adding fructose to an aqueous solution of Pluronic EO106PO70EO106 triblock copolymer (BASF, F127®) followed by hydrothermal treatment at 130 °C. The soft template was then removed by calcination at 550 °C under an inert atmosphere. The obtained carbon materials are several-micrometers in size with a cuboctahedron morphology. TEM micrographs show ordered pore structures with a pore diameter of ~ 4 nm. SAXS pattern analysis shows a relatively sharp peak at q = 0.54 nm-1 confirming the existence of structural regularity. Furthermore, the pore size can be increased by addition of a pore swelling agent (e.g. trimethylbenzene) showing developed mesoporosity. One important feature of the presented materials is the presence of oxygenated surface functional groups (e.g. -OH, -C=O). This allows post modification and introduction of interesting chemical moieties (e.g. functional polymers). This presented synthesis of functional porous ordered carbons via soft templating under such mild conditions is very advantageous since such materials can have important applications in fields like energy storage, drug delivery, catalysis, adsorption and many others.We also report the production of carbonaceous hollow nanotubes using a macroporous alumina membrane (φ ~200nm, Whatman Anodisc 13®) as a hard template. Here, carbohydrate derivative, 2-furaldehyde, is infiltrated into the template's macropore channels and is hydrothermally carbonised at 180 °C followed by the template removal from formed alumina-carbon composite by phosphoric acid. The obtained material has a well-dispersed hollow tubular morphology with the length of several to 10 micrometers and possesses the open pore entrances with the diameter of 120-200nm. Importantly, the tube surface possesses oxygenated functional groups (e.g. -OH, -C=O) and this surface character can be tuned by further calcining the material at different elevated temperatures, showing decreased functionalities at higher calcination temperature as confirmed by FTIR. Simultaneously, aromatisation of the material can be also controlled in this manner, showing the increase in carbon content from 62 to 82 wt % at maximum. The increase in aromatisity is also suggested from the Raman spectroscopy and XPS studies. We further demonstrate grafting of thermoresponsive polymer (Poly-N-isopropylacrylamide) on the carbon tube wall utilising oxygenated functional groups. The turbidimetric analysis of a hydrophilic-hydrophobic changing behaviour of this carbon-polymer composite will be shown, which can be interesting in controlled catch and release in drug delivery system.
9:00 PM - Z4.21
Organic-inorganic Hybridized Cubic Nanoassemblies Comprising Octahedral CeO2 Nanocrystals and Hexanedioic Acid.
Seiichi Takami 1 , Shunsuke Asahina 2 1 , Osamu Terasaki 3 4 , Tadafumi Adschiri 1 Show Abstract
1 , Tohoku University, Sendai Japan, 2 , JEOL (Europe), Croissy-sur-Seine France, 3 , Stockholm University, Stockholm Sweden, 4 , KAIST, Daejeon Korea (the Republic of)
Recent progress in synthetic methods for inorganic nanoparticles has facilitated their application as components for miniaturized devices. One strategy to construct such devices involves the controlled preparation of two-dimensional or three-dimensional periodic assemblies of nanoparticles. We believe that non-spherical nanoparticles should realize various assemblies through anisotropic interparticle interactions. In this presentation, we report the synthesis of cubic nanoassemblies of octahedral CeO2 nanocrystals. Hexanedioic acid (HOOC(CH2)4COOH), which has a carboxyl group at each end of its linear structure, was used as a molecular glue to bind two primary octahedral CeO2 nanocrystals. Scanning electron microscope images showed that the products synthesized with hexanedioic acid had a cubic shape with rugged surfaces. In contrast, the products synthesized without hexanedioic acid were octahedral with smooth surfaces. The X-ray diffraction patterns showed that both products have the CeO2 crystal structure. A high-resolution transmission electron microscope (TEM) images of the cubic products showed that the cubic products were composed of smaller primary octahedral nanocrystals with an average size of ~7 nm. In addition, the TEM images suggested that the primary octahedral nanocrystals assembled together in an oriented fashion. These results suggest that the small primary octahedral CeO2 nanocrystals assembled in an arranged manner to produce cubic nanoassemblies in the presence of hexanedioic acid. Hexanedioic acid possibly bound the primary CeO2 octahedral nanocrystals in a face-to-face manner and realized their ordered assembly. CeO2 has been used in various fields, including catalysis, fuel cells, sensors, and chemical mechanical polishing. New synthetic strategies for CeO2 nanoassemblies that involve altering the specific surface area, mechanical properties, the optical response, etc. should widen their application.
9:00 PM - Z4.22
Heterogeneous Colloidal Clusters of Differently Modified Silica Spheres.
Che Ho Lim 1 , Shin-Hyun Kim 1 , Tae Soup Shim 1 , Seung-Man Yang 1 Show Abstract
1 Chemical and Biomolecular Engineering, KAIST, Daejeon Korea (the Republic of)
Evaporation-driven self-assembly is one of the promising methods to make complex nanostructures due to fast and inexpensive fabrication process. When the monodisperse colloidal particles are dispersed in volatile medium, they form periodic nanostructures as medium evaporates. Since self-assembly of simple spheres produces limited types of nanostructures, however, colloidal clusters which have configurational peculiarity have been investigated for a novel building blocks. When two or more numbers of homogeneous colloidal particles are self-assembled in confined geometry, they are organized into minimal second moment structures. In particular, less than 6 colloidal particles are aggregated into subsets of face-centered cubic (fcc) structure. In this study, we report heterogeneous colloidal clusters which have diverse configurations compared with minimal second moment structures. To achieve this, we used mixture of colloidal particles with two different surface wettabilities. Silica spheres of 1.2 μm in diameter were prepared and modified with dichlorodimethylsilane (DCDMS) and octadecyl-trimethoxysilane (OTMOS), respectively, for different surface wettability. Binary mixtures of the two different silica spheres were dispersed in toluene with 1:1 mixing ratio. For good adhesion between silica spheres after clusterization, solution of polystyrene homopolymer in toluene was added to the mixture of silica dispersion. Then, silica dispersion was emulsified with aqueous Pluronic F108 solution by using homogenizer. Since two silica spheres have different contact angle on toluene droplet, they formed irregular colloidal clusters as toluene evaporated. Moreover, their irregular shapes were determined by the composition of silica spheres. Homogeneous colloidal clusters were prepared and compared with heterogeneous one. While trimer composed of three numbers of homogeneous spheres showed triangular shape, heterogeneous trimer showed ‘Y-shaped’ or ‘T-shaped’ configuration. In case of heterogeneous clusters with more than 3 silica spheres, unusual configurations were observed due to various combinations between two silica spheres. Their various combinations were confirmed by using confocal microscope. Those heterogeneous clusters can act as a colloidal surfactant, and have a potential as a building block for novel structures.
9:00 PM - Z4.24
Fabrication of Hierarchical Janus Pillars and Their Bending Characteristics.
Hyunsik Yoon 1 , Kahp Y. Suh 2 , Kookheon Char 1 Show Abstract
1 School of Chemical and Biological Engineering, Seoul National University, Seoul Korea (the Republic of), 2 School of Mechanical and Aerospace Engineering, Seoul National University, Seoul Korea (the Republic of)
Asymmetric features have recently been of keen interest because of their unique characteristics such as the adhesion hysteresis, the unidirectional wetting and so forth. We present a fabrication method to realize hierarchical and bent Janus nanopillars by the two-step UV-assisted capillary force lithography (CFL) combined with oblique metal evaporation. In order to prepare micropillars, a poly(dimethyl siloxane) (PDMS) mold with micropatterns on the surface was used. UV-curable polyurethane acrylate (PUA) resin placed between the PDMS mold and a substrate was partially cured by the exposure to UV. Due to the oxygen inhibitory effect at the mold/polymer interface, the surface of microstructured PUA pattern remains tacky, whereas the resin beneath the surface is almost fully cured, allowing for the subsequent nanopattern formation on the preformed microstructure without collapse or distortion. A PUA mold with nanopatterns was placed on the preformed micropillars by applying low pressure followed by the second exposure to UV. During the oblique metal evaporation on one side of the PUA pillars (Janus pillars), the nanopillars sitting on the micropillars were bent toward the metal side due to the residual tensile stress while the microbases remained straight because of the diameter dependence on bending degrees. The origin of bending and its direction, such as the difference in thermal expansion coefficients of PUA pillars and metal films as well as the residual stress built up during the metal deposition will be discussed with parameters to control the bending angle.
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Controlling Ice Formation on Microstructured Superhydrophobic Surfaces.
Lidiya Mishchenko 1 , Benjamin Hatton 1 2 , J. Ashley Taylor 3 , Vaibhav Bahadur 1 , Tom Krupenkin 3 , Joanna Aizenberg 1 2 Show Abstract
1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 2 Wyss Institute of Biologically Inspired Engineering, Harvard University, Boston, Massachusetts, United States, 3 Department of Mechanical Engineering, University of Wisconsin, Madison, Wisconsin, United States
Prevention and control of ice nucleation on surfaces is important in many applications, including aircraft efficiency, highway maintenance, and building construction. Yet the science underlying ice formation, which spans several length scales, is poorly understood and few viable anti-icing techniques are currently available. The present work demonstrates that water-repelling microstructured superhydrophobic surfaces can be used to prevent ice accumulation of impacting droplets under icing conditions due to their limited contact time with the substrate. Detailed experimental analysis of the temperature-dependent dynamic droplet/surface interaction shows that the process relies on complete water retraction and bouncing off the substrate before ice nucleation can occur. This mechanism is effective down to approximately -25 to -30°C, above which no ice is formed. Our results are in good quantitative agreement with a simple multi-scale theoretical model involving microscopic heterogeneous nucleation theory and macroscopic wetting dynamics. This study reveals how surface and liquid temperatures, microscale surface feature topography, substrate material properties, and pressure stability should be considered in the design of superhydrophobic surfaces for anti-icing applications. We anticipate that this work will form the foundation for the development of robust, scalable, rationally-designed anti-icing surfaces.
9:00 PM - Z4.26
Directed Rebounding of Droplets by Microscale Surface Roughness Gradients.
Xuemei Chen 1 , Bernard Malouin 2 , Nikhil Koratkar 2 , Amir Hirsa 2 , Zuankai Wang 1 Show Abstract
1 Department of Manufacturing Engineering and Engineering Management, City University of Hong Kong, Hong Kong China, 2 Department of Mechanical, Aerospace and Nuclear engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
Significant progress has been made in engineering robust superhydrophobic surfaces using various fabrication techniques as well as in the fundamental understanding of drop impact behavior on such textured surfaces [1-4]. The works of Wenzel  and Cassie and Baxter  gave rise to nearly ubiquitous models to predict how superhydrophobicity can be achieved with textured surfaces. Many researchers still employ these models in the design and fabrication of textured surfaces. Richard and Quéré  used such textured superhydrophobic surfaces to demonstrate the ability of impacting droplets to completely rebound from the surface, with later computational studies  providing additional insight into the drop impact process. Zheng et al.  took a more analytical approach, developing criteria based upon hydraulic pressure to predict the transition between rebounding and sticking for droplets impacting a surface. Recently, experimental studies have also considered the ability of a droplet to rebound from micro- and nano-textured surfaces [1-4]. These works all examined surfaces with uniform textures, while in the present study we wish to explore the effects of droplet impact on surfaces with non-uniform textures.Here, we extend recent advances in the understanding of droplet rebound from uniformly textured surfaces to a surface with engineered non-uniformities in texture. We demonstrate how these non-uniform superhydrophobic surfaces can be made with a roughness gradient that make it possible to direct or ‘vector’ the rebound of a droplet in a prescribed direction. It was found that rebounding on textured surfaces is significantly influenced by the uniformity of the surface roughness. The presence of a surface roughness gradient sets up a wetting gradient which in turn introduces a prescribed lateral component to the trajectory of a rebounding droplet which was not observed in cases with uniform roughness. The use of surfaces with non-uniform textures may then enable practitioners to control the placement and trajectory of droplets after impact with a surface. This directed droplet rebounding may find application in thermal management of microchips, heat-pipes, self-cleaning, and water harvesting surfaces.References: Y. C. Jung and B. Bhushan, Langmuir 24, 6262 (2008).  T. Deng, K. K. Varanasi, M. Hsu, N. Bhate, C. Keimel, J. Stein, and M. Blohm, Appl. Phys. Lett. 94, 133109 (2009). Z. Wang, C. Lopez, A. Hirsa, and N. Koratkar, Appl. Phys. Lett. 91, 023105 (2007). M. H. Chen, T. H. Hsu, Y. J. Chuang, and F.-G. Tseng, Appl. Phys. Lett. 95, 023702 (2009). R. N. Wenzel, Ind. Eng. Chem. 28, 988 (1936). A. B. D. Cassie and S. Baxter, Transactions of the Faraday Society, 40, 0546 (1944). D. Richard and D. Quéré, Europhys. Lett. 50, 769 (2000). J. T. Hirvi and T. A. Pakkenen, Surf. Sci. 602, 1810 (2008). Q. S. Zheng, Y. Yu, and Z. H. Zhao, Langmuir, 21, 12207 (2005).
9:00 PM - Z4.27
Holographically-defined Titania Electrodes for Dye-sensitized Solar Cells.
Chang Yeol Cho 1 , Woo-Min Jin 1 , Ji-Hwan Kang 1 , Ju-Hwan Shin 1 , Jun Hyuk Moon 1 Show Abstract
1 Chemical and Biomolecular Engineering, Sogang University, Seoul Korea (the Republic of)
Dye-sensitized solar cells (DSSCs) are attractive as potential next-generation photovoltaic devices due to their simple and low-cost fabrication. The engineering titania electrodes with regard to properties such as nanostructure, crystalline morphology, and surface properties are a crucial aspect of efforts to enhance the photoconversion efficiency. Several recent approaches have taken advantage of macroscale morphologies with typical feature sizes on the order of 100 nm. Here, holographic lithography was applied to the fabrication of macroporous titania electrodes for dye-sensitized solar cells. The holographic titania electrode possessed triply periodic bicontinuous macropores, which increased the specific area of titania. We evaluated the performance of the holographically-designed electrodes as possible candidates for use in DSSCs. The construction of holographic electrodes on conventional titania electrodes was also tested for use as a scattering layer for DSSCs.
9:00 PM - Z4.28
Analysis of Partially-cured Imprinting Patterns by Rheometry and Kinetics.
Rhokyun Kwak 1 , Kahp Y. Suh 1 Show Abstract
1 Mechanical Engineering, Seoul National University, Seoul Korea (the Republic of)
UV-curable polymers have been extensively used due to their well-documented benefits such as insolubility of organic solvents and high resistance to heat and mechanical shocks. While traditional use of photopolymerized polymer has been limited to photo-resists, coatings, and adhesives for optical fibers, a range of new applications are emerging in micro-nanofabrication technologies. However, a further study is required as to how thin films are cured and imprinted in terms of transient curing kinetics and rheometric properties. Until now, the photopolymerization reaction has been mainly evaluated on the basis of gelation kineticsTo address the limitations described above, we present here the analysis of transient viscoelastic properties of partially-cured poly(urethane acrylate) (PUA) resin by rheometry and nanoimprinting with controlled partially-cured layer.For generating partially-cured layer with controlled thickness and degree of polymerization, we developed a partial-curing system with a porous mold (PDMS). Due to the penetration of oxygen through the porous mold, a gradient of oxygen concentration is generated in the polymer resin. As a consequence, a partially-cured layer is formed on top of the completely cured layer by controlling curing time (2~8 sec), with the depth ranging from 0 to 4 µm depending on penetration, diffusion and reaction kinetics of oxygen.In this work, viscoplastic properties of partially-cured PUA film are measured by ARES rheometer. Yield stress (0.5~5x103 Pa), which is a representative property of viscoplastic fluid, was observed distinctly in the shear stress curve. Dynamic viscosity with different curing times is also measured. While liquid polymer resin has a constant value, the dynamic viscosity of partially-cured PUA is decreasing as shear rate is increasing. That is, partially-cured PUA is a shear-thinning fluid. This phenomenon is probably because partially linked structures in partially-cured polymer are aligned by shear stress.Imprinting test of partial-cured microscale line structure is also performed according to variations of curing time (10~25 sec) and imprinting pressure (0~3 bars), to visualize partially-cured layer. Prism pattern is imprinted on the partially-cured micro line structures and its depth was measured. The patterned thickness with a fixed imprinting pressure (1 bar) is decreasing from 3 µm to 200 nm with increasing the curing time. Also, saturated patterned thickness is obtained with a high imprinting pressure (~2 bars) because the lower part of the microstructure is completely cured.In conclusion, the characteristics of partial-photopolymerized polymer are well-defined by the highly controllable partial curing system with the help of a porous mold. This study demonstrates the first characterization and visualization of the viscoplastic properties of partially-cured polymer, and thus could be widely used as a reference for various systems using UV-curable polymer.
9:00 PM - Z4.29
Biomimetic Hierarchical Surfaces for Abhesive Applications.
Yi Lin 1 , Christopher Wohl 1 , Marcus Belcher 1 , Brad Atkins 3 , John Connell 2 Show Abstract
1 , National Institute of Aerospace, Hampton, Virginia, United States, 3 Langley Aerospace Research Summer Scholars Program, NASA Langley Research Center, Hampton, Virginia, United States, 2 Advanced Materials and Processing Branch, NASA Langley Research Center, Hampton, Virginia, United States
Abhesion, or the resistance to adhesive interactions, is intrinsic to materials with low surface energies. Abhesive materials have been utilized for a myriad of applications including lab-on-a-chip devices, biofouling, anti-icing of aerospace surfaces, and particulate contamination in MEMS/NEMS fabrication processes. To this end, the surface topology of polymeric materials were modified using either laser ablation patterning or patterned templating. These newly created low energy surfaces were envisioned to be biomimetic surfaces reproducing both the “wet” cleaning properties exhibited by lotus leaves and the “dry” cleaning properties of gecko toes. These approaches result in hierarchical surface topographies that reduce the available surface area for particulate adhesive interactions. The efficacy of these surfaces was investigated using a variety of qualitative and quantitative techniques. For the gecko toe biomimetic surfaces, simulated “stepping” motions were performed on surfaces contaminated with a variety of particulate materials, followed by high resolution SEM imaging. Surfaces were also evaluated based on the ability to shed particulate contamination either by tapping experiments or by running water over inclined surfaces. AFM adhesion force measurements were conducted to investigate single particle interactions quantitatively. Preliminary results indicate that the investigated materials’ relative adhesion force values do not correlate well with surface energy values determined by water contact angle goniometry. This is likely due to factors such as surface elasticity and deformation which are of greater significance for the AFM experiments than the contact angle measurements.
9:00 PM - Z4.3
Multi-scale Slurry Templating for Thermal Wick Material Systems.
Keri Ledford 1 , Jason Nadler 1 , Stephanie Lin 1 Show Abstract
1 Electro-Optical Systems Laboratory, Georgia Tech Research Institute, Atlanta, Georgia, United States
A thermal wick, composed of a low relative density, open-celled copper foam bonded to a copper-clad substrate, is being designed to reliably exhibit high intrinsic thermal conductivity, capillary transport and efficient evaporative cooling across thicknesses less than 500μm. The foam’s micro- and nano- porosity is determined in large part through the use of tailored sacrificial polymer templates in a slurry precursor. On a greater scale, evaporative regions of the wick are enhanced by the incorporation of through-thickness sacrificial templating prior to slurry application. In one approach, negative photoresist patterns are infiltrated with precursor slurry. To distribute the slurry onto the substrate both uniformly and consistently, the application (spin coating) and composition of this precursor were investigated parametrically through rheological measurements. Another approach to obtain enhanced evaporative regions utilizes a positive photoresist as a basis for a diamond monolayer pattern on the substrate. The patterned diamonds are bonded to the copper substrate prior to infiltration with the precursor slurry. Pattern geometries achieved and copper/diamond interfaces investigated.
9:00 PM - Z4.30
The Balancing Act: Engineering Order/Disorder in Multiscale Nanoparticle Arrays for Multiplexed Sensing.
Svetlana Boriskina 1 , Sylvanus Lee 1 , Jacob Trevino 1 , Bo Yan 1 , Linglu Yang 1 , Bjoern Reinhard 1 , Luca Dal Negro 1 Show Abstract
1 , Boston University, Boston, Massachusetts, United States
We will report on the design and applications of multi-scale aperiodic arrays of metal nanoparticles that simultaneously provide broadband near-field enhancement and narrow-linewidth resonant features in their far-field scattering spectra. We have previously demonstrated the capability of lithographically-fabricated aperiodic arrays to generate highly localized intense hot-spots in a broad frequency range and used this feature to develop robust and efficient SERS substrates and colorimetric sensors. For applications such as label-free bio(chemical) sensing, however, narrow-linewidth resonances in the optical spectra of the sensing platform are highly desirable as they provide high resolution of detection. We will demonstrate that plasmonic nano-structures with an optimized degree of disorder can produce narrow-linewidth scattering resonances suitable for label-free detection. We design the k-space of aperiodic lattices to display a number of pronounced diffraction peaks and a dense background of weaker satellites. These features of reciprocal lattices translate into the unique scattering characteristics of the nanoparticles arrays. Namely, scattering of photons on multiple length scales present in the aperiodic lattice results in the broadband total scattering and near-field intensity spectra of the array. On the other hand, the spectral and/or angular shifts of the main diffracted beams corresponding to the pronounced Bragg peaks in the lattice Fourier transform (analogs of grating orders of periodic gratings) can be traced e.g. by measuring the backscattering spectrum of the Gaussian prime array. As a result, aperiodic nano-patterned substrates with pre-designed spectra can be used as multiplexed bio(chemical) sensing platforms. In such platforms, the presence of the analyte can be detected by tracing the shifts of the narrow resonant features, and fingerprinting of molecular targets can be done by probing their Raman and/or fluorescence spectra across a wide frequency range in the visible and near-infrared. We fabricate planar antenna arrays using electron beam lithography on quartz substrates. The far-field scattering characteristics of the fabricated nanostructures are investigated by combining the angularly-resolved and angularly-averaged scattering measurements. Furthermore, we perform SERS and fluorescence enhancement measurements to map the broadband near-field enhancement spectra of the designed antennas. We believe that the unique scattering and field localization characteristics of aperiodic plasmonic nanopatterned arrays pave the way for their use as broadband multiplexed (label-free, SERS and/or fluorescence) sensing platforms for multiple and unspecified molecular targets.
9:00 PM - Z4.4
Structural and Optical Properties of Faujasite-type Zeolite Loaded with ZnO Nanoparticles.
A. Escobedo-Morales 1 2 , Amado Garcia-Ruiz 3 , A. Aguilar 2 , E. Rubio-Rosas 4 , R. Perez 5 Show Abstract
1 Facultad de Ingeniería Química, Benemérita Universidad Autónoma de Puebla, Puebla, Puebla, Mexico, 2 Instituto de Ciencias Físicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, Mexico, 3 UPIICSA-COFAA, Instituto Politécnico Nacional, México, D. F., Distrito Federal, Mexico, 4 Centro Universitario de Vinculación, Benemérita Universidad Autónoma de Puebla, Puebla, Puebla, Mexico, 5 Centro de Física Aplicada y Tecnología Avanzada, Universidad Nacional Autónoma de México, Santiago de Querétaro, Querétaro, Mexico
Zeolites are microporous crystalline aluminosilicates. They are widely used as cracking catalysts and water softening additives for detergents . Their physicochemical properties make them potential materials for environmental health, ion exchange and catalysis. Recently, the possibility to obtain nanocomposites by impregnation of synthetic zeolites with metal or semiconductor nanoparticles has been extensively explored [2-4].Here we present a study concerning the structural and optical properties of faujasite-type zeolite (FAU-NaY) loaded with ZnO nanoparticles. Several concentrations of zinc precursor (0.25, 0.5, 1.0, and 2.0 M) were used to study the effect of ZnO content on the physical properties of the nanocomposites. These were characterized by X-ray diffraction (XRD), scanning and transmition electron microscopy (SEM-TEM), photoluminescence (PL), diffuse reflectance spectroscopy (DRS), and Micro-Raman spectroscopy.X-ray patterns reveal that the zeolitic structure of the support is preserved after the loading process; however the XRD peaks related to the FAU phase decrease on increasing the ZnO content. It was concluded that large zinc salt concentrations (>1.0 M) leads to growth of ZnO nanoparticles, not only inside, but also on the surface of the zeolitic framework. On the other hand, the vibrational properties with the FAU-lattice are strongly affected by the loading process even in the sample of the lowest ZnO content; last is attributed to the strong chemical interaction of oxygen atoms which constitute the zeolitic cages with the trapped ZnO structures.Finally, it was observed that the collected PL spectra of the nanocomposites are dominated by a UV emission centered at about 389 nm attributed to the near band edge (NBE) emission of ZnO. The PL results are complemented with those obtained from DRS. Origins of the observed absorption on-sets are discussed.This work was supported by UNAM-PAPIIT/2010 grant. AEM acknowledges DGAPA-UNAM for the extended postdoctoral fellowship. D. Hu et al. Mater. Res. Bull. 43, 3553 (2008). G. P. Petrova, G. N. Vayssilov, and N. Rösch, J. Phys. Chem. C 112, 18572 (2008). S. Jafari, H. A. Mahabady, and H. Kazemian, Catal. Lett. 128, 57 (2009). M. Takeuchi et al. Appl. Catal. B 89, 406 (2009).
9:00 PM - Z4.6
Silica Particles with Hierarchical Porosity Obtained by Microemulsion Templating.
Nick Carroll 1 , Jhoan Torro-Mendoza 1 , Peter Crowder 1 , Plamen Atanassov 1 , David Weitz 2 , Dimiter Petsev 1 Show Abstract
1 Chemical and Nuclear Engineering, University fo New Mexico, Albuquerque, New Mexico, United States, 2 School of Engineering and Applied Science, Harvard University, Cambridge, Massachusetts, United States
Microemulsion templating is a convenient method for obtaining materials with a hierarchical porosity. Recently we have used this approach to fabricate biporous silica microparticles. The presence of two different pore sizes are due to templating of microemulsion droplets (that give larger pores, about 40 nm in diameter) and surfactant micelles (resulting in smaller pores, about 5 nm). In this study, we examine the dynamics of the formation of these biporous structures. The obtained pore hierarchy may be transient, in some cases leading to a collapse of the internal particle structure. We hypothesize that this is due to coalescence of the small droplets inside the larger drop (that later becomes a microparticle.) In order to obtain a better understanding of the structural evolution and stability, we have performed surface tension and dynamic light scattering measurements of the surfactant/water/oil systems. These experiments provide valuable insights about the time changes of the governing parameters (surface tension, surface charge) and their effect on the phase state of the oil/water/surfactant system. The obtained data are correlated to the final porous structure of the silica particles. The coalescence of small nanometer sized droplets inside the large drop has been modeled by Langevin-Brownian dynamics simulations. The approach takes into account the droplet collision, deformation (film formation) and fusion. Our results offer a better understanding of the kinetics of phase formation and provide additional tools for controlled synthesis of particles with a complex hierarchical internal structure.
9:00 PM - Z4.7
Macroporous Carbon Monoliths with Large Surface Area for Electric Double-layer Capacitor.
George Hasegawa 1 , Kazuyoshi Kanamori 1 , Kazuki Nakanishi 1 , Teiichi Hanada 1 Show Abstract
1 , Kyoto University, Kyoto Japan
The increasing demand for the electrochemical devices, such as batteries, fuel cells, and electric double-layer capacitors (EDLC), has aroused the development of porous carbon materials. It is important that the physical properties of carbon materials, including surface area, pore volume and pore size, are controlled to be suitable for each application, because they are closely related to the electrochemical performance. A practical polarized electrode material for EDLCs is activated carbon with a large specific surface area because EDLCs are based on electrostatic interactions, i.e., the electric charge is accumulated on an electric double-layer of the polarizable electrode, and the electrodes with the larger specific surface area can store more energy. However, the conventional electrodes consisting of microporous carbon particles are not effective because the narrow and disordered pores in-between particles are not suitable for the transportation of ions to the micropore surfaces. In other words, a certain portion of micropores are not accessible for ions and remains unused. For the better capacitive characteristics, therefore, it is indispensable for porous carbons to have the well-defined larger pores (mesopores and macropores) in addition to the micropores. The mesopores and macropores facilitate the diffusion of the electrolyte ions in the materials while the micropores can provide abundant adsorbing sites for ions. Thus, great efforts are focused on the preparation of macro-/microporous, meso-/microporous, and macro-/meso-/microporous carbons for EDLCs. In the MRS fall meeting in 2008, we reported that macroporous carbon monoliths have been successfully prepared from poly(divinylbenzene) (PDVB) networks, which were fabricated by organotellurium-mediated living radical polymerization (TERP) accompanied by spinodal decomposition. We have also reported that the sulfonation of PDVB networks allows mesopores in the co-continuous skeleton to be retained after carbonization. Following activation process by CO2 imparts large surface area with > 2000 m2g-1 to the macro-/mesoporous carbon monoliths, resulting in macro-/meso-/microporous carbon monoliths. In this work, macro-/meso-/microporous carbon monoliths with large surface area are prepared from PDVB networks with relatively large mesopore volume and are characterized as a monolithic electrode for EDLC. Monolithic porous carbons are more advantageous for electrodes of EDLCs rather than traditional porous carbon powders because monolithic carbons solve the problem that electrodes made of carbon powders are easily broken into fragments during the charge-discharge cycles. Besides, monolithic carbons with continuous skeletons can reduce the internal resistance of the electrode as far as the conductivity of the skeletons is made high. Hence, the porous carbon monoliths with large surface area are expected to possess the large capacity and show good cycle characteristics.
Milo S. P. Shaffer Imperial College London
Brian L. Wardle Massachusetts Institute of Technology
Gregory M. Odegard Michigan Technological University
Jun Hyuk Moon Sogang University
Z5: Hierarchically-structured Surfaces
Tuesday AM, November 30, 2010
Room 313 (Hynes)
9:30 AM - **Z5.1
Hierarchically Wrinkled Structures in Multilayered Thin Films.
Pil Yoo 1 Show Abstract
1 School of Chemical Engineering and SKKU Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University, Suwon, Gyunggi-Do, Korea (the Republic of)
Wrinkle formation in layered systems is a ubiquitous phenomenon and is often encountered in modern science and technology. The wrinkles are believed to form spontaneously by the abrupt compressive stress, which is generated when the stress exceeds the critical compressive stress of the system that arises from a mismatch of thermal expansion coefficient between stacked layers. In the thin bilayer system of a metal on a polymer being considered, wrinkles are generated upon heating above the glass transition temperature of the polymer. The characteristics of wavelength and shape of wrinkles can be manipulated by thermomechanical response of polymeric layer and the magnitude of applied strain to the bilayer system. Intriguingly, hierarchically wrinkled structures wherein smaller waves are embedded in larger waves can be generated due to a stepwise stress-relaxation process for the polymeric layer. However, the wrinkling phenomena have been generally treated as defects and degradations in layered structures because of their irregularity and uncontrollability. Controlling the wrinkling so as to produce a desired pattern or architecture is a key issue in the thin film processing and yet only recently has there been studies on utilizing the wrinkling for the purpose of generating regular patterns that could lead to practical applications. It has been shown for this bilayer system that when a patterned polydimethylsiloxane (PDMS) mold is placed on the bilayer of metal and polymer, the externally imposed wave in the form of the periodic pattern causes the wrinkles to self-organize into sinusoidally patterned structures. The internal wave in the bilayer selects the type and number of harmonic modes that contributes to the overall surface shape, thereby permitting shape engineering for anisotropically wrinkled structures. A simple extension of this anisotropic wrinkling to two dimensions can lead to the formation of various complex and hierarchically wrinkled structures that are completely different from the mold pattern. It was found that the work of adhesion of the PDMS mold is a property that can be used to control the phase of the self-organization of bilayer wrinkling. This manipulation additionally enables shape inversion of the self-organized and wrinkled structures. The ability to generate complex patterns or hierarchically wrinkled structures can be facilitated to fabricate unique optical patterns that cannot be made easily using conventional lithographic techniques and can be applied to the production of microlenses. In addition, the resulting complicated patterns can be useful micro-fluidics where channels and micro-sized reservoirs are present.
10:00 AM - Z5.2
Bacterial Biofilm: Natural Hierarchical Surface with Liquid Repellency.
Alexander Epstein 1 , Joanna Aizenberg 1 2 3 Show Abstract
1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 2 Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts, United States, 3 Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, Massachusetts, United States
Most of the world’s bacteria exist in robust, sessile communities known as biofilms, ubiquitously adherent to environmental surfaces from ocean floors to human teeth and notoriously resistant to antimicrobial solutions. Yet biofilms have not been investigated as model functional materials, nor has the relation of their micro/nanoscale surface structures and their macroscopic surface properties been considered. We report the surprising observation that Bacillus subtilis biofilm is extremely nonwetting—capable of repelling both water and lower surface tension liquids—and greatly surpasses the repellency of PTFE. We show the biofilm’s repellent/wetting transition as a function of ethanol concentration as well as its resistance to wetting by other organic solvents and commercial biocides. Previously unreported for any natural surface, these attributes prevent penetration of liquids into the biofilm, as we observe by confocal microscopy. Experiments with mutant biofilms lacking extracellular matrix (ECM) components, thus generating defective topography, show that normal biofilm architecture and composition are required for the nonwetting phenomenon. Furthermore, we consider the role of hierarchical surface features by fabricating chemically functionalized soft lithographic biofilm replicas, adapting a previously developed method. Imaging and analysis of the live and replicated biofilms indicates that the nonwetting properties of the biofilm are a synergistic result of hierarchical reentrant topography and ECM surface chemistry. These remarkable properties of B. subtilis biofilm may guide future advances in bioinspired high performance omniphobic surfaces.
10:15 AM - Z5.3
Surface Characterization of Butterfly Wings.
Nandula Wanasekara 1 , Vijaya Chalivendra 1 Show Abstract
1 , University of Massachusetts, Dartmouth, North Dartmouth, Massachusetts, United States
Surface nanostructure and roughness plays a vital role in controlling the wettability and bouncing of water drops on wings of butterfly/moth species. A detailed experimental study was conducted to investigate the effect of nanostructure on static & dynamic contact angle measurements and coefficient of restitution of four different butterfly wing surfaces. Surface characterization at different length scales was performed using atomic force microscopy (AFM), optical profilometry and scanning electron microscopy. The water drop bouncing experiments were conducted on the surface of butterfly wings to investigate the coefficient of restitution and energy dissipation. Contact angle measurements reveal that the wings which had high roughness factors resulted high static and dynamic (advancing and receding) contact angles. The wings that had a combination of scales and hair-like microtrichia structure showed increased roughness and hydrophobicity compared to wings that had only either one of them.
10:30 AM - Z5.4
Fabrication of Hierarchical Pillar Arrays from Thermoplastic and Photosensitive SU-8.
Shu Yang 1 , Ying Zhang 1 , Chia-Tai Lin 1 Show Abstract
1 Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Bioorganisms offer inspiring marvels to materials scientists as the hierarchical organizations provide remarkable materials properties. Among many hierarchical structures, high-aspect-ratio (HAR) pillar arrays are of interest for applications, including superhydrophobic surfaces, tunable dry adhesion, drug delivery, tissue engineering, and force sensing and actuation, where the surface topography plays an important role. However, fabrication of the hierarchical HAR structures remains rather complicated and limited. By exploiting the thermoplastic and photosensitive nature of SU-8 photoresists, we successfully fabricated different types of hierarchical pillar arrays with variable aspect ratios (height/width, up to 8) through capillary force lithography (CFL), followed by photopatterning. The thermoplastic nature of SU-8 enabled us to imprint micropillar arrays with variable aspect ratios by CFL using a single poly(dimethylsiloxane) (PDMS) mold, simply by tuning the initial film thickness of SU-8 on a substrate. The pillar array was subsequently photopatterned through a photomask, followed by post-exposure bake above the glass transition temperature (Tg) of SU-8. The pillars in exposed region became highly crosslinked, therefore, neither soluble nor reflowable above Tg, whereas the pillars in the unexposed regions could reflow and flatten out. Thus, we investigated two “developing” strategies after UV exposure of SU-8 pillar arrays, including 1) solvent development and drying, and 2) thermal reflow, to create a bi-level hierarchical structures with short pillars and a single-level, dual-scaled HAR pillars in a microdot array, respectively. We believe the study demonstrated here will broaden the applications of imprinting lithography, and offer new routes in fabrication of HAR, complex structures.
10:45 AM - Z5.5
Biomimetic, Hierarchical Polymer Nanostructures and Their Applications.
Philseok Kim 1 2 3 , Alexander Epstein 1 , Wilmer Adorno 1 , Lauren Zarzar 2 , Baptiste Salley 1 , Sylvain Caron 1 , Vaibhav Bahadur 1 , Joanna Aizenberg 1 2 3 Show Abstract
1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 2 Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts, United States, 3 Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, Massachusetts, United States
The surfaces of biological systems often exhibit hierarchically structured architectures performing vital functions for survival. For example, many plant leaves and insect skin have hierarchical structures with feature sizes ranging over multiple length scales. These hierarchical surfaces provide controlled wetting, self-cleaning, suspension and locomotion, collection of water in dry environment, and sensory functions for detection of predators. Mimicking these highly advanced biological hierarchical structures at the same length scale will enable us to create surfaces with unique functions. The main hurdle in mimicking biological hierarchical architectures is the absence of available nanofabrication techniques that can produce features over multi-length scales with high accuracy and throughput. We report on a newly developed nanofabrication strategy, in which a conventional top-down fabrication method is combined with a bottom-up fabrication method. Arrays of high-aspect-ratio polymer micro/nanostructures are fabricated by a series of conventional lithography, etching, and soft lithographic molding method. Subsequently, various conductive polymers such as polypyrrole (PPy), polyaniline (PAni), and polythiophen (PTh) are grown on these ‘parent’ micro/nanostructures by electro- or electroless deposition methods. These procedures produced biomimetic and hierarchical architectures with nontrivial, reproducible morphologies with high throughput. By changing the deposition conditions, various 1D nanofibers, 2D platelets, and complex 3D nanostructures were formed which are difficult to fabricate by conventional nanofabrication methods. These new architectures show unique properties such as high-pressure superhydrophobicity, anti-bacterial properties, and controlled localized condensation behavior. We believe that our new nanofabrication method allows for the fabrication of versatile 3D nano- and microstructures with rich, non-trivial morphologies and finely-tuned sizes that are either impossible or challenging to make using conventional fabrication techniques.
11:00 AM - Z5: Surfaces
Z6: Directed Assembly of Colloids II
Tuesday PM, November 30, 2010
Room 313 (Hynes)
11:30 AM - **Z6.1
DNA-mediated Self-assembly of Small Colloidal Clusters.
Guangnan Meng 2 , Jesse Collins 1 , Natalie Arkus 1 , Michael Brenner 1 , Vinothan Manoharan 1 2 Show Abstract
2 Department of Physics, Harvard University, Cambridge, Massachusetts, United States, 1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
We study the formation and structure of equilibrium colloidal clusters at small particle number (N ~ 10) using optical microscopy. Our experimental system consists of isolated groups of colloidal microspheres with short-ranged attractions. With non-specific depletion interactions, we observe that the number of configurations increases sharply with N. The most favorable states are those with the lowest symmetry. With specific DNA-mediated attractions, the number of states is reduced. Experiments and theoretical calculations suggest that it is possible to direct the assembly of specific structures through multiple competing DNA-mediated interactions.
12:00 PM - Z6.2
The Self-assembly of 2D Surfaces or Membranes from Rod-like Molecules.
Edward Barry 1 , Zvonimir Dogic 1 Show Abstract
1 , Brandeis University, Waltham, Massachusetts, United States
Recently the self-assembly of large (micron to millimeter) 2D fluid-like surfaces or membranes was observed in a simple mixture of rods and polymers. Here, the polymer acts to induce attractive interactions between otherwise entirely repulsive rods (the filamentous bacteriophages fd and M13 viruses), and drives the formation of a wide variety of thermodynamically stable structures, such as membranes. These membranes have properties that are identical to lipid bilayers, and provide an experimental means by which the properties of model membranes can be simultaneously investigated at molecular and continuum lengthscales. In this talk, I will outline conditions under which self-assembly occurs and discuss how we can control and influence self-assembly pathways at all levels of hierarchy ranging from single amino acids of individual rods to the assemblies themselves which contain thousands of rods. Membrane stability under variations in the polymer size and concentration, as well as rod aspect ratio, will be looked at to illustrate the robust and easily scalable pathway for the assembly of nanostructured devices from homogeneous rod-like molecules that these non-amphiphilic membranes present. In addition, I will briefly discuss recent advances that have allowed us to reconstruct the full 3D structure of membranes, and other micron sized assemblages, with nanometer resolution using electron tomography, and determine the response of these equilibrium structures to externally applied forces with optical and holographic tweezers.
12:15 PM - Z6.3
Graphene Oxide-polymer Composites via Emulsion Polymerization.
Suelen Barg 1 , Eduardo Saiz 1 , Ling Wong 2 , Ukrit Thamma 1 , Goki Eda 1 , Angelika Menner 2 , Alexander Bismarck 1 , Manish Chhowalla 2 Show Abstract
1 Materials Department, Center for advanced structural ceramics, Imperial College, London United Kingdom, 2 Chemical Engineering Department, Polymer & Composite Engineering (PaCE) Group, Imperial College , London United Kingdom
Due to its intrinsic mechanical properties (high stiffness and strength), graphene is attractive as a possible reinforcing phase for ceramics and polymers. However, pure graphene is usually fabricated by mechanical exfoliation or by recently reported chemical vapor deposition, both methods are impractical for synthesis of large quantities of graphene required for bulk materials. In contrast, graphene oxide (GO) can be fabricated in bulk quantities through the chemical exfoliation of graphite. Its mechanical properties are similar to those of graphene and the presence of oxygen groups on its surface facilitates functionalization, wet processing and adhesion to host matrices. The main challenge is the development of processing approaches that will allow the controlled incorporation of GO into diverse organic and inorganic matrices in large concentrations.Here emulsion polymerization is used as an efficient process for the incorporation of graphene oxide sheets into polymer matrices for the fabrication of three-dimensional composites of practical dimensions. GO can act as an amphiphile due to the combination of its hydrophilic edges and hydrophobic basal plane. We take advantage of this amphiphile character to prepare Pickering emulsions in which the GO acts as a colloidal surfactant at hydrophilic/hydrophobic interfaces. Measurements of interfacial tension are used to assess the capability of GO to stabilize interfaces. GO-polymer composites in the form of beads, foams and blends with tailored structures and properties can be fabricated by tuning of the amphiphilile character of graphene oxide with regards to the emulsion internal and external phases and controlling the GO concentration.
12:30 PM - Z6.4
Synthesis of Armored Bubbles and Thin Shell Vesicles from Hydrophilic Plate-like Nanoparticles.
Anand Subramaniam 1 , Jiandi Wan 2 , Arvind Gopinath 3 , Howard Stone 2 Show Abstract
1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 2 Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey, United States, 3 Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Nanopowders of graphene oxide, montmorillonite and laponite spontaneously delaminate into ultrathin nanoscopic plates when dispersed in water. These plates, which are typically ~ 1 nm thick and microns in lateral dimension, have found many uses in materials science as precursors to graphene, ceramics, layer-by-layer structures, and as structural modifiers of nanocomposites. However, assembly at fluid/fluid interfaces, a technique that has been fruitful for structuring polymeric and “hydrophobic” nanoparticles, has not been exploited for these materials, probably due to the general view that they are too “hydrophilic” for interfacial adsorption. Here we show that mechanical forces due to shear in a narrow gap can assemble hydrophilic plate-like particles on air bubbles, forming stable nanoplated armored bubbles. Translucent inorganic vesicles (vesicles defined here as closed thin-shelled structures with the same liquid inside and outside) of these particles are produced when the nanoplated armored bubbles are exposed to common water-miscible organic liquids and surfactants. These inorganic vesicles are mechanically robust, have walls that are about six nanometres thick, and are perforated with pores of submicron dimensions. We characterize the phenomenon and find that a wetting transition at the scale of the nanoparticles is the primary mechanism of formation. The discovery of these novel inorganic structures raises a wealth of questions of fundamental interest in materials and surface science.
Z7: Hierarchically-structured Foams
Tuesday PM, November 30, 2010
Room 313 (Hynes)
2:30 PM - Z7.1
Hierarchical Phononic Networks: Controlling Spatial Dispersion over Multiple Length Scales.
Cheong Yang Koh 1 2 , Edwin Thomas 1 2 Show Abstract
1 Materials Science and Engineering, massachusetts institute of technology, Cambridge, Massachusetts, United States, 2 Institute for Soldier Nanotechnologies, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Hierarchical Phononic Networks (HPN) couple geometric and structural features that dominate wave propagation behavior across different length scales; this affords the possibility of an integrated platform providing different wave propagation behavior at different frequency/wavelength regimes and even more interestingly, the possible emergence of new unique propagation behaviors. Our common framework treats all features at multiple length scales on the same footing, allows both the interpretation and design of these structures within the same design scheme and affords a unified and global approach for searching and designing HPN for particular applications.In our approach, we identify and utilize the pertinent symmetries of the designed phononic networks. By selectively breaking these symmetries at the correct length scales, we are then able to sculpt the wave propagation characteristics, for example to induce negative elastic-index behavior at the desired frequencies. This method allows us to cast the spatial dispersion behavior of the system into a framework that naturally transforms between the locality and non-locality of the phonon propagation within these networks and highlights the essential requirements for various kinds of wave propagation behavior, e.g. from resonant negative elastic index to tunneling to complete band gaps. In particular, we show theoretically and experimentally that a geometric structure, comprised of only a single material and air, is able to possess both i) resonant negative index behavior at long wavelengths as in a meta-material, while simultaneously possessing ii) a complete phononic band gap at shorter wavelengths, i.e., the material acts as a phononic crystal for elastic waves. This phenomenon is shown to be general and material class independent within this framework. In addition, it can be extended across structures with various symmetries; we demonstrate our approach for structures with both high and low symmetry. We also show the most general requirements for opening up complete band gaps and why high point group symmetry is not always optimal.Finally, the emergence of new propagation behavior is also demonstrated by combining piecewise building blocks of positive and negative elastic-index materials to achieve effective zero-index behavior, which forms the elastic analog of optical path cancellation. This zero-index behavior is shown to be robust to certain classes of structural disorder in the system.
2:45 PM - Z7.2
Mechanical Performance of Tubular Microtruss Materials Reinforced With Nanocrystalline Sleeves.
Eral Bele 1 , Mishaal Azhar 1 , Glenn Hibbard 1 Show Abstract
1 Materials Science and Engineering, University of Toronto, Toronto, Ontario, Canada
Introduction: Microtruss cellular materials are assemblies of struts with characteristic features in the μm to mm scale, arranged in a periodic, three-dimensional architecture. Compared to conventional cellular architectures (e.g. stochastic foams and honeycombs), they can possess improved structural efficiency, because externally applied loads are resolved axially along the constituent struts. We have recently fabricated composite microtruss materials by electrodepositing reinforcing nanocrystalline sleeves on tubular polymeric scaffolds. These materials can offer enhanced structural performance by exploiting advantageous properties along three length scales: the inherent strength of the electrodeposited material (grain size reduction to the nm scale), its location away from the bending axis of the struts (cross-sectional efficiency in the μm scale), and the spatial arrangement of the struts (architectural efficiency in the mm scale). This study uses finite element analysis and experimental methods to characterize the mechanical properties of these composite materials.Methods: Microtruss pyramidal architectures were constructed from polypropylene tubes; these cores were subsequently bonded to AA3003 aluminum alloy facesheets to create a sandwich construction. Nanocrystalline Ni sleeves (having an as-deposited grain size of ~15 nm) of 100-300 μm thickness were subsequently electrodeposited on these scaffolds. Coated and uncoated samples were then mechanically tested in uniaxial compression; their failure mechanisms were investigated by scanning electron microscopy. Failure was also studied by finite element analysis models using the commercial ABAQUS package.Results: The mechanical properties of the composite material are dependent on three competing failure mechanisms: global strut buckling, local strut buckling and strut-facesheet joint fracture. Analytical models were developed for the first two failure mechanisms, showing the dependence of macroscopic strength on material and geometrical properties. The finite element simulations captured the overall buckling mechanism and showed acceptable agreement with the predicted crushing strength. The stress distribution along the constituent struts showed that the type of failure, and consequently the strength of the composite, is determined by a complex interaction of material properties (e.g. yield strength and hardening coefficient of the electrodeposited sleeve), scaffold-sleeve interfacial strength, and architectural properties of the precursor scaffold.
3:00 PM - Z7.3
Auxetic Elastomers by Design.
Brian Greviskes 1 , Mary Boyce 2 1 , Simona Socrate 2 1 , Christopher Boyce 2 1 Show Abstract
1 , Infinite Corridor Technology, LLC, Winchester, Massachusetts, United States, 2 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
We demonstrate a novel method for designing auxetic elastomeric materials via structuring the material with periodic porous patterns. The patterns are engineered to provide deformation mechanisms including pore opening/closing, ligament bending, and domain rotation and translation tailored to give Poisson’s ratios from zero to large negative values, where the pattern can be tailored to achieve specific values of Poisson’s ratio. The method is described and demonstrated both with simulations and physical representations, both in 2-dimensional and 3-dimensional form. In both cases, the Poisson’s ratios are robust from small to large strain. For the 2-dimensional auxetic substrates, these designs also enable tailoring to allow the substrates to smoothly conform to any complex shape/curvature. Finally, the pores are shown to act as strain relief features, which result in material domains of significantly reduced strain compared to the macroscopic strain. The auxetic designs provide opportunities for novel devices at different lengthscales, ranging from sieves to seals to wave propagation controllers to substrates for stretchable, flexible, and conformable electronics.
3:15 PM - Z7.4
Bio-inspired Hierarchical Composite for Blast Mitigation: Fabrication Methods and Energy Absorption Characterization.
Juliana Bernal Ostos 1 , Renaud Rinaldi 1 , Luke Miller 2 , Chris Hammetter 3 , Biraja Kanungo 1 , Alan Jacobsen 4 , Frank Zok 1 , Galen Stucky 2 1 Show Abstract
1 Materials, UC Santa Barbara, Santa Barbara, California, United States, 2 Chemistry and Biochemistry, UC Santa Barbara, Santa Barbara, California, United States, 3 Mechanical Engineering, UC Santa Barbara, Santa Barbara, California, United States, 4 , HRL Laboratories, Malibu, California, United States
Many systems found in nature are multi-scale, composite materials in which periodicity and porosity are prominent features. Such hierarchy suggests that different mechanisms operate at distinct length-scales, enhancing the mechanical performance of the bulk. We use principles learned from biological materials to design a composite with improved specific energy absorption under compression. In this system, we combine a thiol-ene periodic lattice that has features on the millimeter scale with a polyurethane stochastic foam that has features on the micrometer scale, yielding a polymeric, co-continuous composite. We investigate the energy absorption capabilities of the composite system; a fabrication method has been developed and the compressive stress-strain response of the resulting composite system has been measured experimentally. Quasi-static compression results suggest that the addition of the stochastic polyurethane foam phase leads to a 45% increase in the specific energy absorption of the composite, making this a promising approach for fabricating compressible materials for blast mitigation applications. Insights gleaned from this study will inform the design and fabrication of bio-inspired materials for use in personnel protective systems.
3:30 PM - Z7.5
Structure-property Correlations in Hierarchically-structured, Freeze-cast Composite Scaffolds.
Philipp Hunger 1 , Amalie Donius 1 , Jenell Smith 1 , Theresa Freeman 2 , Ulrike G. Wegst 1 Show Abstract
1 Department of Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania, United States, 2 Department of Orthopedic Surgery, Thomas Jefferson University, Philadelphia, Pennsylvania, United States
Surprisingly few studies have been reported to date on the structure-property correlations observed in freeze-cast materials directionally solidified from polymer solutions and nano- or micro-particle based ceramic or metal slurries. Particularly, no property values have been published thus far for freeze-cast ceramics that are solely glued by a polymeric phase and not processed further by sintering. To investigate both, an alumina-polymer composite was chosen as the model material. Highly porous, hierarchically-structured composites were prepared by freeze-casting to study the effects of particle size, composition and processing parameters on their mechanical properties. While keeping the overall porosity constant, the effect of different freezing rates on pore size and geometry were studied at the first level of the hierarchy of the honeycomb-like structure. While keeping the overall cell wall material composition constant, the influences of particle size and single versus bimodal particle distribution on mechanical properties were investigated at the second level of the hierarchical structure. An increase in freezing rate was found to result in a decrease in lamellar spacing, pore aspect ratio and cross-sectional area of the pores, but not always an increase in both Young’s modulus and plateau strength. The results of this study illustrate several pathways to control both structure and mechanical properties in freeze-cast composites.
3:45 PM - Z7.6
Fabrication of Nano-macro Porous Glass and Glass-ceramic Scaffolds for Hard Tissue Engineering.
Shaojie Wang 1 , Hassan Moawad 1 , Yuliya Vueva 2 , Ahmad Rashad 3 , Manal Saad 3 , Matthias Falk 4 , Mona Marei 3 , Rui Almeida 2 , Himanshu Jain 1 Show Abstract
1 Department of Materials Science and Engineering, Lehigh University, Bethlehem, Pennsylvania, United States, 2 Departamento de Engenharia de Materiais / ICEMS, Instituto Superior Técnico/TULisbon, Lisbon Portugal, 3 Faculty of Dentistry, University of Alexandria, Alexandria Egypt, 4 Department of Biological Sciences, Lehigh University, Bethlehem, Pennsylvania, United States
The bone tissue consists of hierarchical levels of pores over a broad range. A bone scaffold, mimicking the nature, should provide a rigid, biocompatible structure with three-dimensional, interconnected porosity suitable for the migration of mesenchymal stem cells and osteoblasts, rapid vascularization, bone ingrowth and transport of nutrients. For several years, efforts have been underway for the fabrication of such structures with pore size ~ 100 microns. More recently, it has been shown that the performance of these scaffolds will be enhanced in regard to the attachment of cells and supply of nutrients, if there is additional interconnected nanoscale porosity (~10 nm) superimposed on the macroporous structure. Nanoporosity is also crucial for controlling the resorption rate of the scaffold, which should be comparable to the rate of bone growth in the body. In this presentation, we will describe the methods for fabricating such bone scaffolds made of glass and glass-ceramics, with a focus on two methods developed in our laboratory. They are based on melt-quenching and sol-gel techniques for fabricating nano-macro porous structures, both exploiting multiscale phase separation phenomena. In the former method, the composition of glass is selected to be not only biocompatible but also to induce spinodal decomposition on nanoscale which assures interconnectivity of nanopores in the final structure. The glass is then devitrified partially on macroscale by appropriate heat treatment. It is then etched selectively in an acid, leading to nano-macro porosity. After initial success with classic 45S silicate glass, we have expanded the composition region to introduce additional functionality and enhanced bioactivity. In the other method, macroporosity is introduced by superimposing a polymer induced macroscale phase separation on inherently nanoporous gel. In both methods, the final structure consists of multimodal or bimodal distribution of pores ranging from ~10 nm to ~100 micron size. Biocompatibility of the material is verified in vitro by observing the proliferation of MC3T3 bone precursor cells as well as by the in vivo response in animal models.
4:00 PM - Z7: Foams
Z8: Multiscale Carbon Nanotube Composites II
Tuesday PM, November 30, 2010
Room 313 (Hynes)
4:30 PM - Z8.1
Plastic Buckling and Foam-Like Compressive Behavior of Carbon Nanotube Arrays.
Matthew Maschmann 1 2 , Qiuhong Zhang 1 , Liming Dai 3 , Jeff Baur 1 Show Abstract
1 RXBC, Air Force Research Laboratory, Wright Patterson Air Force Base, Ohio, United States, 2 , Universal Technology Corporation, Beavercreek, Ohio, United States, 3 Chemical Engineering, Case Western University, Cleveland, Ohio, United States
The compressive mechanical behavior of carbon nanotube arrays is a critical factor governing their performance in thermal, electrical, and mechanical devices. The behavior of these complex and highly interactive materials, particularly with respect to morphology variations, is currently not well understood. We report the mechanical evaluation of carbon nanotube arrays with heights of 35, 190, 300, 650, and 1,200 µm compressed utilizing flat punch nanoindentation. The flat punch geometry enabled consistent surface area contact for indentation depths to 200 µm. Mechanical response resembled that of open-cell foam materials, with array height playing a similar role as volumetric density in traditional open cell foam materials. The arrays exhibited plastic mechanical yielding initiated at strains between 0.03 – 0.12 and a common compressive elastic modulus, measured via the continuous stiffness method, of between 10 – 20 MPa after yielding. Plastic buckling dominated the deformation of the arrays. The shortest CNT array (35 µm) exhibited “S-shaped” buckle formation, while intermediate heights (190-650 µm) exhibited highly periodic and coordinated buckling initiating from the top surface of the arrays. Finally, the tallest CNT array tested (1,200 µm) exhibited a large buckle near the growth substrate and disorganized buckling near the top surface. Buckle formation is readily identifiable as periodic oscillations within the resulting stress-strain behavior. Lateral force oscillations are also generated during buckle formation and may be of the same order of magnitude as those generated in the compressive direction. The origination point of buckle formation may be phenomenologically explained via foam mechanics and localized CNT morphology. These results offer further evidence of the cellular behavior of CNT arrays and provide significant additional insight into CNT array buckle formation.
4:45 PM - **Z8.2
Developments in Polymer /Carbon Nanotube Composite Films and Fibers.
Satish Kumar 1 Show Abstract
1 , Georgia Institute of Technology, Atlanta, Georgia, United States
The field of carbon nanotubes and polymer/carbon nanotube composites is less than two decades old. In this period, there are more than 50,000 archival publications in the field of carbon nanotubes and more than 5,000 publications in the field of polymer/carbon nanotube composites. By 2014, carbon nanotube market is expected to be a 2 billion dollar market. The incorporation of carbon nanotubes in polymer matrices, results in improvements of many properties. To gain maximum benefit from the presence of carbon nanotubes, they must be as perfect as possible, should be of high purity, must be well dispersed and exfoliated. In addition, carbon nanotube orientation also plays an important role. Carbon nanotubes also act as a template for polymer orientation and nucleating agent for polymer crystallization. Benefits of this ability of carbon nanotube in polymer processing are just beginning to be realized. Results of polymer/carbon nanotube composite films and fibers in author’s laboratory will be briefly reviewed and the potential of producing materials far lighter and stronger than today’s materials will be explored.
5:15 PM - Z8.3
Self Assembly of Carbon Nanotubes to Aramid Fibers for Enhanced Electrical Conductivity.
Gregory Ehlert 1 , Yirong Lin 1 , Henry Sodano 1 Show Abstract
1 School of Mechanical, Aerospace, Chemical and Materials Engineering, Arizona State University, Tempe, Arizona, United States
Traditional aramid fiber reinforced structural composites exhibit low electrical conductivity which can be detrimental in many aerospace applications. Intrinsically conductive polymer matrices have been synthesized to improve the conductivity of the composite; however moderate service temperatures often destroy the conductivity of the matrix. Alternatively, filled polymer matrices can be thermally stable conductive matrices, but these require compromises in other aspects of the matrix properties.Hierarchical carbon nanotube (CNT) fibers offer several advantages over traditional fibers due to the second phase properties. Specifically, the addition of CNTs to the surface of the structural fiber will improve thermal and electrical conductivity along the length of the fiber, which is crucial for multifunctional composite materials. Furthermore, constraining the CNTs to the surface of the fibers will reduce the required mass of CNTs to achieve conductivity. Preliminary results indicate that a CNT weight saving of 60% can be expected in a typical unidirectional lamina by using hierarchical fibers instead of a filled matrix. Polymeric fibers, such as aramid fibers, are typically insulating and stand to gain the most from a method to create hierarchical fibers; however the typical harsh growth environment (>700°C) of CNT is not appropriate for the fiber due to the polymeric nature of the fiber. In order to enhance the electrical and thermal conductivity of the polymeric fiber reinforced composite without decaying the fiber, this paper will present a method to self assemble carbon nanotubes to aramid fibers to create hierarchical aramid fibers. The aramid fibers are first functionalized by to create amine surface groups. Carbon nanotubes are then endcap functionalized through a strong oxidation procedure to create acyl chloride groups on the end of the carbon nanotubes. When dispersed in acetone, the carbon nanotubes can then be self