Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session B18: Focus Session: Templated Assembly of Polymers |
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Sponsoring Units: DPOLY Chair: Alamgir Karim, University of Akron Room: 319 |
Monday, March 16, 2009 11:15AM - 11:51AM |
B18.00001: Directed Assembly of Biological Polymers Invited Speaker: The self-assembly of polypeptides into beta-sheet rich nanofibrils has attracted considerable attention in recent years to both understand amyloidgenesis and for their potential biomaterials applications. This self-assembly process is generic to all proteins where fibrillation is typically induced under harsh conditions of low pH and/or high temperature, which are of course not suitable for biomaterials applications. Here we will outline the method developed in our laboratory to create thermo-reversible fibrillar hydrogels from aqueous solutions of a series of proteins by adding a reductant. Proteins studied include beta-lactoglobulin, ovalbimum, lysozyme and bovine serum albimum; all contain an increasing number of disulfide bridges that are disrupted by the reductant. Such disruption destabilises the native state of the protein and this allows us to form transparent, self-supporting hydrogels under physiological conditions. The potential to control and manipulate the gel properties, including mechanical strength and structure (fibre diameter and mesh size of hydrogel) has been explored by varying the protein (consequently the number of disulfide bridges), protein concentration, reductant concentration and ionic strength of the matrix. Our results will be presented here and similarities and differences highlighted. Furthermore we will present both our 2- and 3-dimensional cell culture experiments that show the gel matrix promotes both fibroblast and chondrocyte cell spreading, attachment and proliferation; indicating our hydrogels gels are biocompatible and they can provide a viable support for different cell types. [Preview Abstract] |
Monday, March 16, 2009 11:51AM - 12:03PM |
B18.00002: Hydroxyapatite growth induced by self-assembled noncollageneous extracellular protein: a study on biomineralization \textit{in vitro} Xiaolan Ba, Yizhi Meng, Nadine Pernodet, Sue Wirick, Chris Jacobsen, Helga F\"uredi-Milhofer, Yi-xian Qin, Miriam Rafailovich, Elaine DiMasi Little is known about the role of various ECM proteins in the formation of calcium phosphate during the biomineralization. Here we follow the calcium phosphate mineralization process in vitro using two different ECM proteins, fibronectin and elastin. The mechanical properties of the protein fibers during the early stages were probed by shear modulation force microscopy. The development of the mineral crystals along the protein matrices was investigated by scanning electron microscopy, soft x-ray scanning transmission microspectroscopy, and grazing-incidence synchrotron x-ray diffraction. The elastic modulus of the fibers in the elastin-fibronectin mixture increased to a greater extent than that of the fibers from a single protein. In the presence of fibronectin, longer exposure in the mineral solutions led to the formation of hydroxyapatite crystals templated along the self-assembled fiber structures, while elastin fibers collected calcium without crystallizing. Ca L-edge XANES spectra confirm that Ca in the Ca-elastin complex lacks the mineral anion coordination found in the fibronectin systems and in Ca mineral controls. [Preview Abstract] |
Monday, March 16, 2009 12:03PM - 12:15PM |
B18.00003: Replication of Optical Microstructures of \textit{Papilio palinurus} through Biomimicry Mohan Srinivasarao, Matija Crne, Vivek Sharma, John Blair, Jung Ok Park, Christopher J. Summers The coloration of animals in nature is sometimes based on their structure rather than pigments. Structural coloration based on diffraction, multilayer reflection, cholesteric analogues or photonic crystal-like structures is pervasive especially in the world of insects. The color of \textit{Papilio palinurus} results from microbowl lined with a multilayer of air and chitin. The green color is the result of color mixing of the yellow light reflecting from the bottom of the bowl and the blue light reflecting from the sides of the bowl. We have used breath figure templated assembly as the starting point to mimic the structure of \textit{Papilio palinurus}. We were able to produce microbowls which were then coated with a multilayer of alternating titanium oxide and aluminum oxide. The resulting structure exhibits the same color mixing as the original butterfly structure does. [Preview Abstract] |
Monday, March 16, 2009 12:15PM - 12:27PM |
B18.00004: Polyelectrolyte and nanoparticle adsorption to nanopatterned surfaces Thuy Chastek, Steven Hudson, Vince Hackley The adsorption of polyelectrolytes and nanoparticles onto patterned and curved surfaces is investigated (by fluorescence and electron microscopy) and exploited to produce anisotropic patchy particles. Various anisotropic properties are necessary for the self-assembly of complex structures. In this work, particles were bound temporarily to a substrate, so that part of their surfaces is occluded during subsequent surface modification by the adsorption of polyelectrolyte. The substrate surface charge has a significant effect on the adsorption of particles, which provided several advantages in comparison to bare glass substrates. These include much reduced deposition time, a high degree of coverage, and the ability to accommodate both negatively and positively charged particles. Moreover, patch production yield is consistently 99 $\pm $ 1 {\%}. Rapid coating methods transferable to roll-to-roll processing were tested, and step-by-step characterization methods to evaluate yield were developed. High-yield site-specific binding of complementary spheres to the lithographic region of patchy particles and surfaces was demonstrated, including binding to positive and negative patches. [Preview Abstract] |
Monday, March 16, 2009 12:27PM - 12:39PM |
B18.00005: Vertical Alignment of Single Wall Carbon Nanotubes (SWNTs) in Thin Polymer Films Meagan Mauter, Menachem Elimelech, Chinedum Osuji Thin polymer films (1-10 um) incorporating singly dispersed, vertically aligned carbon nanotubes have a diverse set of potential applications. Desalination membranes that use aligned SWNT as pores, for instance, are predicted to exhibit high flux and salt rejection through size exclusion of hydrated ions. Current fabrication techniques, however, are unable to realize the vertical assembly of narrow diameter SWNTs. Here, we direct the vertical alignment of SWNTs in thin films by using magnetic field aligned lyoptropic surfactant mesophases as structure directing templates. The short alkyl tails of the surfactant impart negative diamagnetic anisotropy to worm-like micelles and lead to parallel alignment of the liquid crystalline (LC) director in an applied magnetic field. The nanotubes orient preferentially with their long axis parallel to the director field of the mesophase, thus promoting their vertical alignment in the system. The LC mesophase incorporates monomers that are polymerized by UV exposure after nanotube alignment to form the polymer matrix. X-ray scattering and optical spectroscopy are used to characterize the field-guided assembly process. The present system may have additional applications for polymer reinforcement using carbon nanotubes. [Preview Abstract] |
Monday, March 16, 2009 12:39PM - 12:51PM |
B18.00006: STM study of stereoselective oligomeric chains on cobalt oxide templates Daejin Eom, Hui Zhou, Kwang T. Rim, Michael Lefenfeld, Colin Nuckolls, George W. Flynn, Tony F. Heinz Stereoselective oligomeric chains of cis-1,4-poly(2,3-dimethyl-1,3-butadiene) have been grown using the cobalt oxide surface as a template. The chains were formed by vacuum deposition of the monomer on an oxidized Co(0001) surface held at room temperature. The geometric structure of the 1-dimensional chains and their relationships to the structure of the surface were probed using scanning tunneling microscopy (STM). The typical chains were more than 10 monomer units in length and were highly linear in structure. When the chains were annealed to a temperature of 480 K, however, their morphology abruptly changed to irregularly shaped curves. We interpret this transformation as the result of scission of the methyl side groups of the oligomers. In addition to comprehensive STM topography data, we have investigated the chains using scanning tunneling spectroscopy (STS). The STS spectra show features with an energy spacing of 0.17 eV. We interpret this response as arising from an inelastic tunneling channeling involving excitation of the symmetric deformation mode of the methyl side groups. [Preview Abstract] |
Monday, March 16, 2009 12:51PM - 1:03PM |
B18.00007: Breath-figure-templated assembly of holey polymer films Vivek Sharma, Mohan Srinivasarao Breath figures formed on evaporating polymer solutions exposed to the blast of humid air involve growth and self-assembly of water drops that are non-coalescent. The hexagonally close packed, nearly monodisperse drops, eventually evaporate away, leaving a polymer film with ordered array of pores. We provide the first quantitative attempt aimed at the elucidation of the mechanism of this breath-figure-templated assembly. The dynamics of drop nucleation, growth, noncoalescence and self-assembly are modeled by accounting for various transport and thermodynamic processes. The theoretical framework developed in this study allows one to rationalize and predict the structure and size of pores formed in different polymer-solvent systems under given airflow conditions. [Preview Abstract] |
Monday, March 16, 2009 1:03PM - 1:15PM |
B18.00008: Gelation in Semiflexible Polymers Venkat Padmanabhan, Sanat K. Kumar Discrete Molecular Dynamics/Collision Dynamics has been employed to study the formation of a physical gel by semi-flexible polymer chains. The formation of a geometrically connected network of bundles of chains is investigated as a function of temperature. As the temperature is lowered, a percolated homogeneous solution phase separates to form a non-percolated nematic fluid and upon further decrease in the temperature, it goes back to a percolated gel state. The gelation, at lower temperatures, is due to the dynamic arrest of chains, preventing them from completing the phase separation process. The cooling rate also plays an important role in deciding the final outcome. Quenching the system, to the final temperature, at a faster rate yields gelation while slower quenches result in phase separation. [Preview Abstract] |
Monday, March 16, 2009 1:15PM - 1:27PM |
B18.00009: Highly Ordered Block Copolymer Templates for the Generation of Nanostructured Materials E. Bhoje Gowd, Bhanu Nandan, Nadja C. Bigall, Alexander Eychmuller, Manfred Stamm Among many different types of self-assembled materials, block copolymers have attracted immense interest for applications in nanotechnology. Block copolymer thin film can be used as a template for patterning of hard inorganic materials such as metal nanoparticles. In the present work, we demonstrate a new approach to fabricate highly ordered arrays of nanoscopic inorganic dots and wires using switchable block copolymer thin films. Various inorganic nanoparticles from a simple aqueous solution were directly deposited on the surface reconstructed block copolymer templates. The preferential interaction of the nanoparticles with one of the blocks is mainly responsible for the lateral distribution of the nanoparticles in addition to the capillary forces. Subsequent stabilization by UV-irradiation followed by pyrolysis in air at 450 $^{\circ}$C removes the polymer to produce highly ordered metallic nanostructures. This method is highly versatile as the procedure used here is simple, eco-friendly and provides a facile approach to fabricate a broad range of nanoscaled architectures with tunable lateral spacing. [Preview Abstract] |
Monday, March 16, 2009 1:27PM - 1:39PM |
B18.00010: Polymeric nanocomposite comprising size-controlled organic nanostructures via copolymer-directed self-assembly Dequan Xiao, Kunhua Lin, Qiang Fu, Qinjian Yin Inspired by inorganic nanomaterials, low-dimensional organic nanostructures have emerged as a new field of nanomaterials with the presence of size-dependent physical properties. Here, we report a polymeric nanocomposite comprising size-controlled organic nanostructures, formed by copolymer-directed self-assembly. By TEM and SEM images, we found the near-spherical shapes of the zero-dimensional organic nanoparticles. A strongly broadened Raman shift band was probed, suggesting the presence of size-dependent quantum confinement effect. By proof-of-principle quantum chemical calculations, we further explain that the strong Raman broadening is caused by the heterogeneous size-distribution of the organic nanoparticles. The present polymeric nanocomposite opens a new route for exploring low-dimensional organic nanostructures with size-dependent physical properties. [Preview Abstract] |
Monday, March 16, 2009 1:39PM - 1:51PM |
B18.00011: Orientational Change of Microphase-Separated Domains of Block Copolymer Thin Films Placed on Ordered Nanoparticle Monolayers Kookheon Char, Taehee Kim Orientation of microphase-separated domains of diblock copolymer (BCP) thin films deposited on ordered nanoparticle (NP) monolayers was investigated. Ordered NP monolayers were prepared on silicon substrates with the Langmuir-Blodgett deposition technique. Parallel orientation of anisotropic microdomains (cylinders and lamellae) of BCP thin films with respect to the substrate is preferred on bare silicon substrates due to the preferential enthalpic interaction with one of BCP blocks, while the perpendicular orientation is preferred on the lattice-like ordered NP monolayers due to the roughness induced from the NP monolayers which can exert elastic deformation on the parallel-oriented microdomains, suppressing the substrate-induced parallel orientation. The effects of NP size as well as BCP film thickness on the orientation of BCP domains were systematically studied with AFM and Grazing Incidence Small-Angle X-ray Scattering (GISAXS). The rectification of perpendicularly oriented BCP microdomains onto underlying NP lattices was analyzed with SEM for thin BCP films (less than 100 nm in thickness). With this experimental technique, we observed the persisted perpendicular orientation of BCP microdomains on NP vacant sites up to the width of NP vacant sites less than 290 nm ($\sim $ 11 L$_{o})$. [Preview Abstract] |
Monday, March 16, 2009 1:51PM - 2:03PM |
B18.00012: Directed self-assembly of block copolymers for resolution enhancement and pattern rectification Joy Cheng, Charles Rettner, Daniel Sanders, Alshakim Nelson, Hoa Truong, Ho-Cheol Kim, William Hinsberg Directed polymer self-assembly which combines lithographically defined substrates and self-assembled polymers has been considered as a potential candidate to extend conventional lithography techniques. Self-assembled block copolymer domains can multiply the spatial frequency and improve pattern quality of the underlying resist prepattern. Lamella-forming PS-b-PMMA is spin-cast on patterned substrate with alternating stripes of resist/ neutral underlayer and annealed to generate well-aligned microdomains. The performance of directed self-assembly depends on the pitch of resist prepattern and resist pattern quality. For linear line-space pattern, defect-free frequency doubling can be achieved within $\pm $5{\%} mismatch between periodicity of block copolymers and pitch of resist patterns. Less mismatch tolerance was observed in concentric circular pattern. The self-healing capability of block copolymers has been explored by introducing dotted resist lines. Pattern rectification and frequency multiplication can be successfully achieved when sufficient local spatial information is given in the resist prepattern. [Preview Abstract] |
Monday, March 16, 2009 2:03PM - 2:15PM |
B18.00013: Tetragonal Ordering in Block Copolymer-Homopolymer Blend Films Laterally Confined in a Square Well Su-Mi Hur, Carlos Garc\'Ia-Cervera, Ed Kramer, Glenn Fredrickson Self-consistent field theory (SCFT) simulations are presented for a melt blend of AB diblock copolymers and A homopolymers in a thin film confined to a square well. The work aims to guide self-assembly towards tetragonal ordering, which is a pattern of technological interest in block copolymer lithography. By using suitable A homopolymer additives, we have succeeded in achieving square lattices of cylinders not observed in the confined or bulk pure diblock system. A phase diagram is presented that shows the region of stability of the tetragonal phase as a function of chain length and volume fraction of the homopolymer additive, in addition to several other interesting phases that result from a competition between surface and bulk contributions to the free energy. Results are also presented on the effect of line edge roughness in the square confinement well on the achievement of robust and defect free tetragonal order. [Preview Abstract] |
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