Symposium Organizers
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
Session Chairs
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
1 Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States, 2 Mechanical Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractPolymers 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
1 Chemistry , University of Toronto, Toronto, Ontario, Canada
Show AbstractThe 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
1 Materials Science and Engineering, University of Illinois, Urbana, Illinois, United States
Show AbstractThe 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
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11:30 AM - **Z1.4/Y1.4
Plasmonic Metamaterials: From Negative-index Materials to Photovoltaics.
Albert Polman 1
1 , FOM Institute AMOLF, Amsterdam Netherlands
Show AbstractMetamaterials 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
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
Show AbstractNanostructured 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
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
Show AbstractPhotocatalytic 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
2 Electrical Engineering, University of Cambridge, Cambridge United Kingdom, 1 EECS, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractA 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
1 , Kyung Hee University, Yongin Korea (the Republic of)
Show AbstractRecently, 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
Session Chairs
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
1 Chemistry, University of Toronto, Toronto, Ontario, Canada, 2 Chemistry, University of North Carolina, Chapel Hill, North Carolina, United States
Show AbstractSelf-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
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
Show AbstractOrdered 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
1 Department of Mechanical Engineeirng, M.I.T., Cambridge, Massachusetts, United States
Show AbstractOrdered 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
1 Applied Physics and Applied Mathematics, Columbia Univeristy, New York, New York, United States
Show AbstractA 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
1 Chemical and Biological Engineering, Tufts University, Arlington, Massachusetts, United States, 2 Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractWe 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
1 Department of Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, Maryland, United States
Show AbstractTo 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
BREAK
Z3: Multiscale Carbon Nanotube Composites I
Session Chairs
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
1 R&D, Nanocomp, Concord, New Hampshire, United States
Show AbstractMacroscale 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
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
Show AbstractCarbon 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
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
Show AbstractThe 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
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
Show AbstractLong 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
Session Chairs
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
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
Show AbstractPorous 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
1 Chemistry Department, SUNY Binghamton University, Binghamton, New York, United States
Show AbstractMany 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
1 Chemistry, Sungkyunkwan University, Suwon Korea (the Republic of), 2 SKKU Advanced Institute of Nanotechnology, Sungkyunkwan university, Suwon Korea (the Republic of)
Show Abstract 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
1 Department of Polymer Science and Engineering, University of Massachusetts Amherst, Amherst, Massachusetts, United States
Show Abstract 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.[1] 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.[1]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.[2]Atomic transfer radical polymerization (ATRP)[3] 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: [1] Nagarajan, S.; Russell, T.P.; Watkins, J.J. Adv. Funct. Mater., 2009, 19, 2728.[2] Bates, F.S. Science, 1991, 251, 898.[3] Davis, K.A.; Charleux, B.; Matyjaszewsk, K. J. Polymer Sci. Polymer Chem., 2000, 38, 2274.
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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
1 Chemistry, State University of New York, Binghamton University, Binghamton, New York, United States
Show Abstract 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.
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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
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
Show AbstractBy 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.
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Solvothermal Synthesis of Highly Hierarchical Urchin-like LiFePO4 Mesocrystals and LiFePO4/C Composites.
Jelena Popovic 1 , Markus Antonietti 1 , Maria-Magdalena Titirici 1
1 Colloids, Max Planck Institute of Colloids and Interfaces, Potsdam Germany
Show AbstractMesocrystals as described by Cölfen et al. [1] 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. [2], 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. [1] Cölfen H, Antonietti M, Mesocrystals: Inorganic Superstructures Made by Highly Parallel Crystallization and Controlled Alignment, Angew. Chem., Int. Ed. 2005; 44(35):5576-5591; [2] Padhi, AK., Nanjundaswamy KS, Goodenough JB, Phospho-olivines as Positive-Electrode for Rechargeable Lithium Batteries. J. Electrochem. Soc. 1997
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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
1 Chemistry, Uinversity of Illinois at Chicago, Chicago, Illinois, United States, 2 Physics, Uinversity of Chicago, Chicago, Illinois, United States
Show AbstractRecently, freestanding membranes of ligated nanoparticles have been prepared and investigated [1]. 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 [2]. We also discuss the self-assembly of ligated nanoparticles, nanorods, and nanodiscs in the interior of the hydrated phospholipid membranes [3].[1] 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[2] Chan, Henry; Kral, Petr (in preparation)[3] Titov, Alexey; Chan, Henry; Kral, Petr (in preparation)
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Templating with Silver Nanoparticle Morphologies: Gold plating, Shells, and Frames.
Matthew McEachran 1 , Vladimir Kitaev 1
1 Chemistry, Wilfrid Laurier University, Waterloo, Ontario, Canada
Show AbstractSilver 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 [1], pentagonal rods [2], prisms [3] and cubes/bi-pyramids [4]. 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 [5] 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 [6]; (ii) frames in surfaced enhanced Raman (SERS) [7], and (iii) plating in optics and electronics [7]. 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.[1] Pietrobon, B.; Kitaev, V. Chem. Mater. 2008, 20, 5186-5190. [2] Pietrobon,B.; McEachran, M.; Kitaev, V. Acs. Nano 2009, 1, 21-26.[3] Cathcart, N.; Frank, A.; Kitaev, V. Chem. Commun. 2009, 7170-7172[4] McEachran, M; Kitaev, V.. Chem. Commun. 2008, 5737-5739[5] Sun, Y.; Mayers, B. T.; Xia, Y. Nano Lett. 2002, 2, 481. Sun, Y.; Xia, Y. Science, 2002, 298, 2176[6] Skrabalak, S.; Chen, J.; Au, L.;, Lu, X.; Li, X.; Xia, Y. Adv. Mater., 2007, 19, 3177[7] Shipway, A..; Katz, E.; Willner, I. Chem. Phys. Chem. 2000, 1, 18–52.
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Nanostructured Carbohydrate-derived Carbonaceous Materials.
Shiori Kubo 1 , Robin White 1 , Markus Antonietti 1 , Maria-Magdalena Titirici 1
1 Colloid department, Max Planck Institute of Colloids and Interfaces, Potsdam-Golm Germany
Show AbstractWe 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.
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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
1 , Tohoku University, Sendai Japan, 2 , JEOL (Europe), Croissy-sur-Seine France, 3 , Stockholm University, Stockholm Sweden, 4 , KAIST, Daejeon Korea (the Republic of)
Show AbstractRecent 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.
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Heterogeneous Colloidal Clusters of Differently Modified Silica Spheres.
Che Ho Lim 1 , Shin-Hyun Kim 1 , Tae Soup Shim 1 , Seung-Man Yang 1
1 Chemical and Biomolecular Engineering, KAIST, Daejeon Korea (the Republic of)
Show Abstract 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.
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Fabrication of Hierarchical Janus Pillars and Their Bending Characteristics.
Hyunsik Yoon 1 , Kahp Y. Suh 2 , Kookheon Char 1
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)
Show AbstractAsymmetric 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
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
Show AbstractPrevention 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 und