Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session N17: Adsorption Phenomena |
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Sponsoring Units: DPOLY Chair: Hide Yokoyama, Advanced Industrial Science and Technology, Japan Room: Colorado Convention Center 102 |
Wednesday, March 7, 2007 8:00AM - 8:12AM |
N17.00001: Adsorption of polymers on colloid particles Dadong Yan, Shuang Yang, Charles C. Han, An-Chang Shi The adsorption of homopolymers on spherical particles with a strong attractive potential has been studied within the self-consistent field theory. The particles are immersed in concentrated polymer solutions and the structure of the adsorbed polymer layer has been examined as a function of the particle size, focusing on the average loop and tail length at different bulk concentrations and solvent qualities. The scaling relationship between the average tail/loop length and the degree of polymerization has also been investigated. It is found that the average loop length is insensitive to the particle size, while the average tail length depends strongly on the particle size. In particular, tails become longer for smaller particles or larger surface curvatures. It is argued that this size effect may provide a mechanism for the excess entanglements induced by adding nanoparticles to polymer solutions. [Preview Abstract] |
Wednesday, March 7, 2007 8:12AM - 8:24AM |
N17.00002: Colloidal Lithography and Particle Decoration Metrology Steven Hudson, Thuy Chastek, Barry Bauer The self-assembled organization of particles depends on the symmetry of their interactions, and strides are being made in producing nanoparticles of controlled shape and functionalization. Here we use particle adsorption to control and detect surface modification, particle symmetry and shape. We have studied ways to achieve a random sequential adsorption of polystyrene (PS) spheres to make asymmetric particles on charged polyelectrolyte films. After coating the spheres with an oppositely charged layer and releasing them from the charged film, they had a small charged patch on their surface. This provided sufficient area to associate with a single oppositely charged particle of comparable size, and resulted in the controlled formation of asymmetric doublets. Additionally, a strategy that added oppositely charged particles, which were smaller than the charged surface patch on the PS spheres, was used to measure the size of the exposed charged area. [Preview Abstract] |
Wednesday, March 7, 2007 8:24AM - 8:36AM |
N17.00003: Adsorption and Fractionation of RAFT-polymerized PS-b-PMMA Block Copolymers for 2D Liquid Chromatography Junwon Han, Chang Y. Ryu, Ho-Cheol Kim, Greg Breyta, Hiroshi Ito Polymer adsorption in nanoporous silica is important for the advancement of polymer separation and purification techniques. In particular, we will demonstrate how understanding of the polymer nanopore adsorption can be applied for (1) a quantitative analysis of block copolymers using the adsorption-based interaction chromatography and (2) a large scale fractionation of block copolymer using a simple gravity column of silica gel. Our target polymers for the analysis and fraction are polystyrene-block-poly(methyl methacrylate) diblock copolymers (PS-b-PMMA) synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. PMMA precursors with phenyldithiobenzoate end group are used as a macromolecular chain transfer agent for the RAFT polymerization, and the contents of PS and PMMA homopolymers in the RAFT PS-b-PMMA block copolymers have been quantitatively analyzed by a solvent gradient interaction chromatography technique. Specifically, we have employed both bare silica and C18-bonded silica columns for the 2-dimensional chromatography analysis and large scale fractionation of the block copolymers in terms of their chemical heterogeneity. [Preview Abstract] |
Wednesday, March 7, 2007 8:36AM - 8:48AM |
N17.00004: Direct Fluorescence Measurements of Polymer Surface Diffusion and Intramolecular Rearrangements Janet Wong, Liang Hong, Sung Chul Bae, Steve Granick A picture is emerging, based on few-molecule fluorescence spectroscopy, of polymer surface dynamics at the solid-liquid interface. Here we describe experiments using fluorescence correlation spectroscopy (FCS) and F\"{o}rster Resonance Energy Transfer (FRET) of polystyrene (PS) and polyethylene oxide (PEO) adsorbed from good solvent. In-plane translational diffusion of these polymers was measured as a function of molecular weight and surface coverage. We show the surface diffusion (D) decreases with molecular weight in a power law fashion with exponent equal to -3/2 in the regime of dilute surface coverage. The surface coverage ($\Gamma )$ effect on D is even more intriguing, with an initial increase with $\Gamma $and then decreases after a critical $\Gamma $ is achieved. Exploring the hypothesis that the change in D reflects chain conformational change as $\Gamma $ increases, experiments are underway that employ FRET to quantify the chain end-to-end separation. [Preview Abstract] |
Wednesday, March 7, 2007 8:48AM - 9:00AM |
N17.00005: Brownian diffusion close to polymer brushes Benoit Loppinet, Emma Filippidi, Vassilik Michailidou, George Fytas, Juergen Ruehe Brownian diffusion of diluted colloidal particles of different sizes was investigated by evanescent wave dynamic light scattering in the vicinity of polystyrene polymer brushes grafted to a glass surface. The particles concentration profiles, resolved from the penetration depth dependence of the scattered intensities, evidenced an excluded region close to the glass hard wall with a characteristic size increasing with the brushes grafting density. The dynamic of large hard spheres particles (R=120nm), excluded from the brushes, was slowed down though slightly faster than the hard wall case. Smaller polystyrene microgels particles (R=16 nm and 42nm) that partially penetrated the brushes, presented a very slowed down dynamics, much more so for the smaller particles, reminiscent of size exclusion type of mechanism. [Preview Abstract] |
Wednesday, March 7, 2007 9:00AM - 9:12AM |
N17.00006: Displacer Effects on Pre-adsorbed Polystyrenes In Nanoporous Silica Chang Y. Ryu, Chansu Kim, Joel Batson, Sanat Kumar The addition of low molecular weight displacers has been used to probe the nature of adsorbed polymer chains on surfaces, and we have employed the displacers to understand the adsorption of polystyrene (PS) onto nanopores of silica particles in cyclohexane. When the radius of gyration (Rg) of PS is smaller than the pore radius (Rp) of the nanoporous silica, the displacement behavior of PS on nanopore surfaces is in quantitative agreement with that of PS on flat surfaces. However, when Rg of PS is larger than Rp of nanopores, the addition of displacers after preadsorbing PS in nanopores has increased the surface access of PS by a factor as large as 100{\%} -200{\%}, depending on the relative size ratio of Rg/Rp. On the contrary, when the displacers are mixed with cylcohexane prior to the PS adsorption in small nanopores, the surface access of PS is monotonically dependent of the composition of displacers. This suggests that the larger PS chains adsorbed in smaller pores are kinetically entrapped with severely limited mobility, and the addition of displacers will facilitate the diffusion of PS in nanopores by inducing a weaker surface binding and swelling of the congested PS chains in nanopores. [Preview Abstract] |
Wednesday, March 7, 2007 9:12AM - 9:24AM |
N17.00007: Theory of the adsorption of polymers onto chemically non-uniform surfaces with applications to the polymer adsorption onto the mixed brushes. Alexander Chervanyov, Gert Heinrich By developing the self-consistent perturbation expansion we theoretically study the adsorption of polymers onto the chemically non-uniform planar surfaces. The present theory deals with both regularly and randomly patterned surfaces having the position-dependent affinity for polymers. We predict that chemical non-uniformity of the surface dramatically enhances the overall affinity of this surface for polymers. The corresponding effective adsorption potential is calculated as a function of the periodicity of the surface-to- the size of polymer ratio and the excluded volume parameter. The obtained results are applied to the study of the adsorption of polymers onto the selective binary brushes that assume different morphologies. As a main result of the study, we demonstrate that the reversible switching from random to `ripple' microphase of the binary brush results in the significant enhancement of the adsorption ability of this brush. [Preview Abstract] |
Wednesday, March 7, 2007 9:24AM - 9:36AM |
N17.00008: Effect of Silane Sizing on Polymer-Glass Adhesion Moshe Gottlieb, Haim Dvir Glass slides sililated with organofunctional silanes were used to study polymer-glass interaction strenth. The extent of surface coverage, surface properties and topology were experimentally determined for the different silane treatments. For the different polymers were deposited on the silane treated glass the strength of polymer interaction with the silane treated glass was investigated using contact-mode Atomic Force Microscopy and the adsorbed layer thickness was determined optically. Typically, for each polymer a characteristic layer thickness was measured irrespective of the silane treatment or strength of adhesion. Adhesion strength was attributed mainly to van der Waals interactions with no indications of large scale covalent bonding between the polymer and the surface. The interaction strength and affinity of the polymer to the surface is dominated by hydrophobic/hydrophilic interactions and hydrogen bonds between grafted side groups and the functional groups of the silane treatment. [Preview Abstract] |
Wednesday, March 7, 2007 9:36AM - 9:48AM |
N17.00009: Dynamic Self-Assembly of Polymers from a Sphere-on-Flat Geometry Zhiqun Lin, Suck Won Hong, Jun Xu Self-assembly of micro- and nano-scale materials to form ordered structures promises new opportunities for developing miniaturized electronic, optoelectronic, and magnetic devices. In this regard, several elegant methods based upon self-assembly have emerged, for example, self-directed self-assembly and electrostatic self-assembly. Dynamic self-assembly of nonvolatile solutes via irreversible solvent evaporation has been recognized as an extremely simple route to intriguing structures. However, these dissipative structures are often randomly organized without controlled regularity. In this presentation, we will show a simple, one-step technique to produce well-ordered structures (e.g., concentric rings) consisting of polymers with unprecedented regularity by allowing a drop of polymer solution to evaporate in a sphere-on-flat geometry. This technique, which dispenses with the need for lithography and external fields, is fast, cost-effective and robust. As such, it represents a powerful strategy for creating highly structured, multifunctional materials and devices. [Preview Abstract] |
Wednesday, March 7, 2007 9:48AM - 10:00AM |
N17.00010: Monte Carlo Simulations of the Selective Adsorption of Heteropolymers on Heterogeneous Surfaces Jesse Ziebarth, Jennifer Williams, Yongmei Wang Lattice Monte Carlo simulations are used to study the selective adsorption of self-avoiding walk heteropolymers on heterogeneous surfaces near the critical adsorption point, the point at which polymer chains just become adsorbed to a surface. The critical adsorption point, determined as the polymer-surface interaction energy for which adsorption is least dependent on chain length, is identified for several different copolymer chain sequences on several surfaces with different site distributions. Selective adsorption is defined as the ability of a surface to more strongly adsorb chains with a certain sequence over chains with other chain sequences. It is found that highly patchy and alternating surfaces are able to selectively adsorb blocky and alternating chains, respectively, while surfaces with a random distribution of sites do not selectively adsorb any chains. Additionally, it is shown that adsorption is most selective for low chain concentrations and relatively weak adsorption energies. [Preview Abstract] |
Wednesday, March 7, 2007 10:00AM - 10:12AM |
N17.00011: The breaking of chiral symmetry using long-range electrostatic forces Kevin Kohlstedt, Francisco Solis, Graziano Vernizzi, Monica Olvera de la Cruz Surface charge heterogeneities result in the adsorption of oppositely charged amphiphilic molecules along charged fibers. The competition of this two-component system between electrostatic interactions, favoring ionic structures, and the net incompatibility of the co-assembled species, favoring macroscopic segregation, leads to local segregation and the formation of periodic patterns along the surface. We analyze the symmetry and size of the surface patterns on the surface of cylindrical structures. Lamellar patterns are arranged into helical structures along the cylinder, breaking the chiral symmetry. We also describe the critical transition between periodic patterns and macroscopic segregation. The characteristic domain size $L_0$ jumps discontinuously to infinity, resulting in macroscopic phase segregation of the components, at the critical salt concentration $\kappa_c$. The dependence of $\kappa_c$ on the helical pitch angle $\theta$ of the lamellar is shown. Our results suggest a new physical method to separate patterned ionic fibers with different pitch angles by modifying the salt concentration. [Preview Abstract] |
Wednesday, March 7, 2007 10:12AM - 10:24AM |
N17.00012: Activated Desorption of Water from a Polymer Surface Carolina C. Ilie, P.A. Jacobson, I.N. Yakovkin, L.G. Rosa, Matt Poulsen, D. Sahadeva Reddy, J.M. Takacs, S. Ducharme, Peter A. Dowben We studied water adsorption and desorption on the dipole ordered polymer poly(methylvinylidene cyanide) PMVC. The polymer has a distinct bulk absorbed water phase. The absorption of water is believed to distort the polymer chain placement. The kinetic parameters are obtained from thermal desorption spectra. Arrhenius plots yield the activation energy and the order of desorption process is determined from the best linear fit in the Arrhenius plots. Unusual angular dependence in thermal desorption is also observed. [Preview Abstract] |
Wednesday, March 7, 2007 10:24AM - 10:36AM |
N17.00013: Understanding Polymer Adhesion: First-principles calculations of the adsorption of organic molecules onto Si surfaces Karen Johnston, Risto M. Nieminen The adhesion of plastics to ceramics is important for many industrial and technological appliations. It is therefore essential to understand the underlying structure and bonding of the polymer and the surface. The aim of this research is to improve plastic adhesion using a multiscale approach. The first step involves the use of density functional calculations to understand the atomic-scale structure and bonding of polymers on surfaces. The plastic of interest is mainly composed of the polymer bisphenol-A-polycarbonate (BPA-PC). The BPA-PC monomer consists of two phenol groups, one propane group and a carbonic acid group. First-principles calculations of the adsorption of these molecules onto the Si(001)-(2$\times$1) dimer surface will be presented. Finally, the incorporation of first-principles data into a coarse-graining method will be discussed. [Preview Abstract] |
Wednesday, March 7, 2007 10:36AM - 10:48AM |
N17.00014: Quartz Microbalance Measurement of Adsorption Potential Well-Depths Ryan Foltz, Rafael Garcia Changes in the resonant frequency of a quartz crystal microbalance (QCM),can be used to measure film thicknesses on the order of 0.1 monolayer or less that are adsorbed on the microbalance's electrode surfaces. The well-depth of the adsorption potential for molecules on a flat surface is a key parameter for determining the wetting transition temperature for molecules on that surface. However, it is a difficult quantity to predict with precision using theoretical models. We will examine the viability of using the adsorption on the QCM at low pressures to determine the well-depth of the adsorption potential for for nitrous oxide and other polar molecules on flat surfaces. We will compare our data with available theoretical predictions. [Preview Abstract] |
Wednesday, March 7, 2007 10:48AM - 11:00AM |
N17.00015: Phonon-induced Anisotropy in Dispersion Forces on a Metallic Substrate Je-Luen Li It is known that surfactant micelles spontaneously adsorb on gold (111) surfaces with orientational order dictated by the gold crystal structure. All this happens despite the screening effects of delocalized electron clouds in metallic systems. To understand the van der Waals forces that provide organization on metallic substrates, we describe a formalism wherein the dielectric response acquires directional dependence through phonon dispersion relations related to the crystal structure. In metals, ionic screening is enhanced along certain directions and a crystalline metallic substrate generates both torque and attraction on geometrically asymmetric objects. Numerical calculations show that the anisotropic van der Waals force will orient a dielectric rod-like micelle on a gold (111) surface. [Preview Abstract] |
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