Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session Z19: Focus Session: Polymer Brushes |
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Sponsoring Units: DPOLY Chair: Chanjoong Kim, Kent State University Room: B118-B119 |
Friday, March 19, 2010 11:15AM - 11:51AM |
Z19.00001: Design and applications of functionalized polymer brushes Invited Speaker: Response to stimuli is one of the major life processes, by which living systems interact with the external environment. Advances in nanotechnology have focused on designing ``responsive to stimuli'' or ``smart'' materials that mimic many processes found in living systems. The talk addresses our recent results on the synthesis, study, interesting applications and prospects of functionalized polymer brushes for the fabrication of smart responsive surfaces, sensors with various transduction mechanisms, micro/nanoactuators, and electrochemical gating devices. We also use surface modification of nanoparticles with polymer brushes for a new intriguing opportunity to turn on and off and tune interactions between nanoparticles, allowing control of the directed self-assembly with external stimuli/signals. The stimuli responsive polymeric and hybrid systems demonstrate strong advantages for the fabrication of robust multifunctional and multiresponsive materials and nanodevices. [Preview Abstract] |
Friday, March 19, 2010 11:51AM - 12:03PM |
Z19.00002: Mixed Polymer Brushes: A Tool for Nano-lithography? Su-Mi Hur, Amalie Frischknecht, Dale Huber, Glenn Fredrickson Self-consistent field theory (SCFT) simulations are presented that examine the suitability of mixed polymer brushes as a nano- lithography tool by adapting lateral confinement methods that have proved effective in enhancing the in-plane order of self- assembled block copolymer films . In the present context, however, we explore a type of ``chemical'' (rather than ``topological'') confinement in which a ``pure'' polymer brush of either A or B homopolymer is used to laterally confine the mixed A/B brush into a region of prescribed shape. SCFT simulations of such confined mixed brushes show that the introduction of a pure polymer brush alongside the mixed brush region directs the microdomains to align with the interface between the two regions. Results are also presented that demonstrate the possibility of forming features with multiple sizes and pitches in precise locations within a film by modulating the grafting densities of one or both mixed brush components. [Preview Abstract] |
Friday, March 19, 2010 12:03PM - 12:15PM |
Z19.00003: Mechanical Properties of Polystyrene Brush Films Andrew Clough, Yoshihisa Fujii, Zhaohui Yang, Ophelia Tsui Fifteen years ago, Fredrickson et al. [\textit{Macromolecules} \textbf{1992,} 25, 2882-2889] predicted that a molten polymer brush possesses a shear modulus that would cause the surface structure to deviate from that of a liquid. Their predictions, though broadly used, have been largely unchecked. Here, we present experimental data on polystyrene PS brushes that validate Fredrickson et al.'s predictions. Measurement obtained by following the time evolution of the surface structure of a brush shows that the shear modulus of the brush is established prior to the onset of the terminal flow regime, suggesting that the entropic elasticity in the brush chains needed to bring about the solid behavior of the brush is operative already in the rubbery regime. [Preview Abstract] |
Friday, March 19, 2010 12:15PM - 12:27PM |
Z19.00004: Diblock-copolymer brush tethered to a nanoparticle Bart Vorselaars, Mark M. Matsen, Jaeup Kim, Tanya L. Chantawansri, Glenn H. Fredrickson We model a brush of diblock copolymers grafted to a spherical nanoparticle, using self-consistent field theory (SCFT). This is achieved with a computationally fast algorithm that combines a pseudo-spectral method for solving the diffusion equation in spherical-polar coordinates and Anderson mixing to iterate the self-consistent field equations. The self-assembling block-copolymer films coat the nanoparticles with a variety of periodic surface patterns, which can be tuned by changing the various system parameters. Results are compared to previous SCFT calculations on flat surfaces, and it is seen that the curvature and finite surface area of the nanoparticle shifts the phase boundaries and introduces additional phase transitions. These patterned nanoparticle coatings are expected to have promising future technological applications. [Preview Abstract] |
Friday, March 19, 2010 12:27PM - 12:39PM |
Z19.00005: Adsorption of end-adsorbing homopolymers A and B from solution onto a solid interface Folusho Oyerokun, Richard Vaia Determination of the composition and spatial organization in multicomponent monolayers formed by the adsorption of polymeric ligands from solution is important in variety of applications. Prior studies on adsorption of end-functionalized homopolymers show that the final surface coverage depends on the molecular weight, the solution concentration, adsorption energy of the terminal group and degree of polydispersity of the polymer chains. This study addresses the thermodynamics of adsorption of end-adsorbing homopolymers A and B onto a flat surface from solution. Specifically, we examine the role of solvent selectivity, incompatibility between the A and B segments, and the degree of bidispersity on the structure of the adsorbed layers. The relevance of our findings to synthesis of multivalent nanoparticles (nanoparticles with two or more types of ligands attached to their surfaces) by immersion of the nanoparticles into a solution containing the various ligands will also be presented. [Preview Abstract] |
Friday, March 19, 2010 12:39PM - 12:51PM |
Z19.00006: Grafted Peptides for the Control of Interfacial Properties William Ducker, Wade Mosse, Sally Gras Peptide or protein polymers that are used to control interfacial properties are usually prepared by solid-state synthesis and then adsorbed to an interface. Such a method results in a low yield and places restrictions on polymer structure, because the peptide must be designed to adsorb, as well as to provide the interfacial control. The method of grafting peptides from surfaces is an alternate method that is potentially very useful because the peptide is covalently linked, and the sequence limitations related to adsorption are removed. To demonstrate this technique, we have used solid-phase peptide synthesis to graft a 15-residue peptide, EKEKEKEKEKEKEGG, containing a zwitterionic sequence of alternating lysine and glutamic acid residues from the surface of an aminosilanized silicon wafer by placing the silicon wafer within a commercial microwave peptide synthesizer. We confirmed the presence of this peptide layer on the surface by X-ray photoelectron spectroscopy (XPS) and ellipsometry. Atomic force microscopy (AFM) was then used to study the forces between the peptide-modified surface and a borosilicate glass sphere as a function of solution pH. We will also discuss the use of grafted peptides to control the stability of colloidal suspensions. [Preview Abstract] |
Friday, March 19, 2010 12:51PM - 1:03PM |
Z19.00007: Strong Polyelectrolyte Brushes: A self-consistent field theory study Gabriele Migliorini, Mark Matsen We investigated the properties of a polyelectrolyte brush system by means of self-consistent field theory. We considered the case of a polyelectrolyte system grafted to both a similarly and oppositely charged surface, in the presence of counter-ions. The properties of the system are described, in the weakly charged limit, by saddle point equations, that couple a modified diffusion equation to the one-dimensional Poisson-Boltzmann equation, describing the electrostatic field in the system. A systematic, numerical study of this set of equations is presented and comparison is made with previous studies. Possible extensions to different grafting geometries are suggested and throughout discussed. [Preview Abstract] |
Friday, March 19, 2010 1:03PM - 1:15PM |
Z19.00008: Protein adsorption at polyethylene oxide brushes of various surface coverage Warren Taylor, Richard Jones The adsorption of proteins onto surfaces enables the unwanted formation of Bio-films that are detrimental to a wide range of applications as diverse as artificial implants and the hulls of ocean liners. A surface that exhibits excellent protein resistant behavior is polyethylene oxide brushes (PEO). The amount of adsorbed protein at a brush surface is related to the grafting density and molecular weight of the PEO chains. However it has not yet been proven experimentally where the proteins adsorb and therefore why the brush offers resistance to adsorption. There are three suspected modes of adsorption; ``primary'', at the substrate, ``secondary'', at the edge of the brush and ``tertiary'', within the brush. Recently theoretical work by Katira et al has proposed a random sequential model, explaining the adsorption of proteins at brushes. In this theory the proteins adsorb at random surface sites, which are not covered by the brush. As the surface coverage of the chains increases, the number of available adsorption sites decreases. This theory is in agreement with experimental work carried out in our group. [Preview Abstract] |
Friday, March 19, 2010 1:15PM - 1:27PM |
Z19.00009: Surface Dynamics of Untethered Chains on top of Chemically Identical Polymer Brushes Bulent Akgun, Gokce Ugur, Zhang Jiang, Suresh Narayanan, Sushil Satija, Mark D. Foster The dynamics of the surface height fluctuations on untethered chains spun cast on chemically identical homopolymer brushes are studied using X-ray photon correlation spectroscopy (XPCS) and neutron reflectivity (NR). These dynamics are found to be well described by theory of overdamped capillary waves. Underlying brush layer alters dramatically the dynamics of the film surface of PS chains atop the brush. Surface dynamic behavior strongly depends on the interpenetration of free chains into the brush layer which is dictated by the thickness of untethered chains, thickness and grafting density of the brush layer. Increase of underlying brush thickness or decrease of brush grafting density, increases the interpenetration of free chains into the brush layer and increases relaxation time constants. The interpenetration depth decreases with increasing molecular weight of untethered chains. [Preview Abstract] |
Friday, March 19, 2010 1:27PM - 1:39PM |
Z19.00010: Molecular Dynamics Simulations of Fractionation of Molecular Brushes During Spreading on Substrates Jan-Michael Carrillo, Andrey Dobrynin, Sergei Sheiko We have performed coarse-grained molecular dynamics simulations of motion of brush-like molecules in a matrix of linear chains in contact with a substrate under Poiseuille flow conditions. Our simulations show that short brush molecules move faster than the long ones resulting in fractionation of the brush molecules according to their molecular weight in the spreading polymeric films. The simulation data are in a good qualitative agreement with the predictions of the theoretical model which relates the brush velocity with the ratio of the friction coefficients between brush and substrate and between substrate and linear chains and brush geometric characteristics (length of the brush molecule and its width). Computer simulations and theoretical model provide an explanation of the brush fractionation observed during spreading of the mixtures of brush-like and linear macromolecules on a solid substrate. [Preview Abstract] |
Friday, March 19, 2010 1:39PM - 1:51PM |
Z19.00011: Surface Diffusion of Single Molecules on Poly(N-isopropylacrylamide) Brush Surfaces Shengqin Wang, Y. Elaine Zhu How molecules and macromolecules diffuse at polymer surface remain inadequately understood. In this talk, we present a recent single-molecule spectroscopy study of fluorescent probes molecules at surface-tethered polymer brush surfaces. We focus on the dynamics of fluorescent molecules, Rhodamine110 (RG110) on thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) brush thin films as a model system of tunable molecule-polymer surface interactions by varying temperature (T) across the LCST of PNIPAM brushes. The diffusion coefficient, D of RG110, measured by fluorescence correlation spectroscopy (FCS) at a single molecule resolution, decreases as increasing the solution T across the LCST of PNIPAM brush thin films, due to the enhanced hydrophobic interaction at the molecule-polymer interfaces. However, it is surprising to observe the faster diffusion of RG110 on the self-assembled monolayer of octadecyltriethoxylsilane (OTE) than that on the PNIPAM brush surface, despite the stronger RG110 interaction with OTE than PNIPAM. Additionally, we observe that reduced PNIPAM brush thickness lead to further slowing down the diffusion dynamics of RG110 on PNIPAM brush surfaces at constant T. We thus speculate that the retarded diffusion process of small molecules on soft polymer brush surfaces, in comparison to the faster diffusion on hard surfaces, is a result of the coupling between molecule surface diffusion and the relaxation of wiggling polymer brush chains at the interface. [Preview Abstract] |
Friday, March 19, 2010 1:51PM - 2:03PM |
Z19.00012: Structure of End-Grafted Polymer Brushes -- A Molecular Dynamics Study Ian Elliott, Tonya L. Kuhl, Roland Faller Molecular dynamics simulations of a polar polymer brush in a polar solvent are presented using a coarse-grained approach. Chain extension is heavily influenced by temperature as expected. Chains extend far from the surface at high temperature, while surface adsorption at a weakly attractive surface dominates at low temperature. Increasing grafting density leads to greater chain extension due to excluded volume effects under all conditions, consistent with previous scaling analysis. Polymer depletion regions are found near the surface even at very high grafting densities indicating a chain orientation normal to the surface close to the grafting points. Radial distribution functions reveal that the grafting pattern does not affect the overall brush configuration beyond the first five monomers of each chain as long as the surface is homogeneously covered. [Preview Abstract] |
Friday, March 19, 2010 2:03PM - 2:15PM |
Z19.00013: First principles Modelling of Brush formation of linear oligomers on Al Surfaces Colin Denniston, Lingti Kong, Martin Mueser We study the role of chemical detail in short-linear parafins and olefins in the formation of polymer brushes on an Aluminum substrate. The presence of unsaturated bonds near the end of the chain greatly enhances the brush formation on the Al surface. In addition we examine the resulting change in slip boundary conditions for flow over the surface. Our simulations are based on a molecular dynamics force field we have developed using force matching to density functional theory with careful attention to correct reproduction of lateral as well as normal forces. [Preview Abstract] |
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