Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session Y19: Surfaces and Adsorption I |
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Sponsoring Units: DPOLY Chair: Zhiqun Lin, Iowa State University Room: 320 |
Friday, March 20, 2009 8:00AM - 8:12AM |
Y19.00001: Sequence-directed organization in self-assembled monolayers of beta-peptides on solid surfaces: A Monte Carlo simulation study Jagannath Mondal, Bong June Sung, Arun Yethiraj The sequence-directed organization of self-assembled monolayers (SAM) of amphiphilic $\beta$-peptides adsorbed on gold surfaces is studied using Monte Carlo simulations. A phenomenological model is considered where each (helical) molecule is represented by a rigid nano-rod with the side groups at appropriate locations. This model effectively distinguishes between two, namely globally amphiphilic (GA) and non-globally amphiphilic(non-GA), sequence-isomers of an amphiphilic $\beta$ peptide Y-(ACHC-ACHC-K)$_3$. The simulations show that the GA isomers have a high degree of orientational order that is not exhibited by the non-GA isomers, consistent with experiment. The simulations quantify a subtle balance between electrostatic, hydrophilic, and hydrophobic interactions on the self-assembly of $\beta$-peptides on surfaces. [Preview Abstract] |
Friday, March 20, 2009 8:12AM - 8:24AM |
Y19.00002: Thermal Response of PNIPAM Brushes Studied by Numerical Self-Consistent Field Calculations Dong Meng, Qiang WANG Unlike most polymers, poly(N-isopropyl acrylamide) (PNIPAM) exhibits a lower critical solution temperature in water, i.e., PNIPAM chains are soluble (expand) at low temperatures and insoluble (collapse) at high temperatures. This property has been used to create ``smart'' surfaces of PNIAPM brushes that can switch wettability, porosity and cell-adhesion properties as temperature is changed. Such thermal response of PNIPAM brushes are strongly affected by both chain length and grafting density. In this study we use numerical self-consistent field calculations with a composition-dependent Flory-Huggins parameter obtained from experiments to study the thermal response of PNIPAM brushes. The effects of chain length and grafting density are systematically investigated to provide guidance to experimental design of PNIPAM brushes for targeted applications. [Preview Abstract] |
Friday, March 20, 2009 8:24AM - 8:36AM |
Y19.00003: Time evolution of the structure of fluorinated alkanes near solid surfaces Mesfin Tsige The study of thin films of physisorbed molecules has attracted much experimental and theoretical interest in the past few decades. This is mainly due to numerous reports of anomalous behavior in the structural and dynamical properties of polymer thin films at interfaces and the expected consequences in their wide range of practical applications. Although great advances have been made in our understanding of the physics and chemistry of polymer melt/solid and polymer melt/vapor interfaces, there remain a number of fundamental as well as practical issues that need to be addressed regarding the influence of interfaces on a polymer film. One of the issues, which I think no systematic study has been yet conducted on, is the stability or time-evolution of the molecular layering in a film next to a solid surface. The main focus of my presentation will be on our recent computer simulation study result that shows that the extent of layering in an alkane film next to a solid substrate may oscillate in time with an amplitude and period that strongly depends on temperature. [Preview Abstract] |
Friday, March 20, 2009 8:36AM - 8:48AM |
Y19.00004: Activation of CO$_{2}$ on transition metal surfaces and oxide supported metal thin films Sujata Paul, Marco Buongiorno Nardelli Using first principles simulations based on Density Functional Theory, we have investigated the adsorption and activation properties of CO$_{2}$ on a variety of transition metal surfaces and oxide supported metal thin films. We intend to focus on the chemical conversion of CO$_{2}$ through heterogeneous catalysis using surfaces and interfaces where there is nanoscale control over charge density at the reactive sites. The activation of CO$_{2}$ on clean metal surfaces is possible at very high temperatures and the situations changes drastically when reaction happens on oxide supported metal thin film. The chemical reactivity of the molecule on the surface depends on the charge rearrangement at the metal-alkaline earth oxide interface. We want to understand the possible catalytic systems and characterize the relevant geometrical and electronic parameters related to the reaction mechanisms, rates and yield. [Preview Abstract] |
Friday, March 20, 2009 8:48AM - 9:00AM |
Y19.00005: Dynamics of an Adsorbed Polymer Chain Joshua Kalb, Sanat Kumar Because of the current precision in fluorescent labeling, it is possible to label single polymers such as DNA or PEG and track their dynamical and equilibrium properties in the bulk as well as near attractive surfaces [Maier et. al., Macro. 2000][Sukhishvili et. al., Macro. 2002]. Recent evidence from these experiments and related simulations has shown that the dynamics of a single polymer near an attractive surface appear diffusive, however further evidence coming from the 'diffusion coefficient' implies a different process other than diffusion is at work such as reptation, `hover crafting', or `hopping' [Sukhishvili et. al., Macro. 2002]. In general, these possible dynamical behaviors are determined by the length of the polymer itself as well as the microscopic details of the attractive surface which include the density, strength, and distribution of attractive surface sites[Desai et. al., PRL 2007][Qian et. al., PRL 2007]. In this presentation, we investigate the effects of microscopic surface sites on single polymer dynamics through DMD simulations and compare these results to the properties of the chain in the bulk and near a flat attractive surface. [Preview Abstract] |
Friday, March 20, 2009 9:00AM - 9:12AM |
Y19.00006: Investigation of Carboxymethyl Cellulose Adsorption onto Regenerated Cellulose Surfaces via Quartz Crystal Microbalance with Dissipation Monitoring and Surface Plasmon Resonance Spectroscopy Zelin Liu, Paul Gatenholm, Alan Esker The adsorption of anionic polyeletrolytes, sodium salts of carboxymethyl celluloses (CMC), with different degrees of substitution (DS = 0.9 and 1.2) from aqueous electrolyte solutions onto regenerated cellulose surface was studied via quartz microbalance with dissipation monitoring (QCM-D) and surface plasmon resonance (SPR). The influence of both calcium chloride (CaCl$_{2})$ and sodium chloride (NaCl) was examined. Both QCM-D and SPR results indicate that CMC adsorption onto regenerated cellulose surfaces increases with increasing electrolyte concentration and CaCl$_{2}$ (divalent cation) showed a significant effect on CMC adsorption compared to NaCl (monovalent cation) at the same ionic strength. Voigt-based viscoelastic modeling of the QCM-D data and analysis of the SPR data are consistent with the existence of a swollen CMC layer on the cellulose surface with a viscosity of $\sim $1.3×10$^{-3}$ kg m$^{-1}$ s$^{-1}$ and an elastic shear modulus of $\sim $10$^{5}$ kg m$^{-1}$ s$^{-2}$. [Preview Abstract] |
Friday, March 20, 2009 9:12AM - 9:24AM |
Y19.00007: Theory of Polymer Adsorption Onto Selected Chemically Patterned Substrates. Alexander Chervanyov, Gert Heinrich We theoretically studied the reversible adsorption of polymers onto selected rigid and soft chemically non-uniform substrates with an emphasis on the polymer adsorption onto the selective binary mixed brushes. In the course of our study, we developed two independent theoretical methods, the self-consistent perturbation expansion and the transfer operator formalism, which made it possible to thoroughly investigate the density structure of polymers adsorbed onto chemically non-uniform substrates. As successive stages of our research, we applied the above theoretical methods to the study of the polymer adsorption onto the selected substrates, as follows: (i) periodically patterned rigid surface; (ii) randomly patterned rigid surface; (iii) surface that bears an array of periodically distributed adsorption centers; (iv) ripple, random and dimple morphologies of the binary mixed brush. By comparing the results obtained for the above listed systems we derived the qualitative trends that are common for the polymer adsorption onto the investigated chemically non-uniform substrates. In this talk, we discuss what are the main factors that influence the polymer adsorption onto the patterned substrates and how to reduce/enhance the polymer adsorption by way of manipulating these competitive factors. [Preview Abstract] |
Friday, March 20, 2009 9:24AM - 9:36AM |
Y19.00008: Cationic xylan adsorption onto self-assembled monolayers and model cellulose surfaces Alan Esker, Abdulaziz Kaya, Daniel Drazenovich, Wolfgang Glasser, Katrin Schwikal, Thomas Heinze Self-assembly of cationic hydroxypropyltrimethylammonium xylans (HPMAs) with different degrees of substitution (DS) onto self-assembled monolayers (SAMs) and model cellulose surfaces has been investigated by surface plasmon resonance (SPR). Maximal adsorption of HPMAs onto COOH-terminated SAMs occurs at an intermediate DS=0.10. Ionic strength effects on adsorbed amount follow different trends at low and high DS values which qualitatively agree with predictions of scaling theory for polyelectrolyte adsorption. For adsorption onto model cellulose surfaces and OH-terminated SAMs, surface excess values are relatively low compared to COOH-terminated SAMs. For adsorption onto CH$_{3}$-terminated SAMs, solubility of the HPMAs plays an important role as HPMA adsorption decreases with increasing DS values. [Preview Abstract] |
Friday, March 20, 2009 9:36AM - 9:48AM |
Y19.00009: Introduction of a novel surface plasmon resonance imaging method for use in the study of quantitative kinetic surface interactions Scott Allen, Oleh Tanchak, John Dutcher The surface plasmon resonance (SPR) phenomenon is widely used as a surface sensitive probe of biomolecular surface interactions. SPR imaging (SPRi) is an experimental mode that takes advantage of the SPR phenomenon to directly visualize nanoscopic changes to surfaces using simple optics and a CCD camera. SPRi, performed at a fixed angle of incidence, enables one to study association, dissociation and degradation processes in a multi-arrayed format without the need for fluorescent tags. A discussion of specific challenges associated with performing kinetic measurements at a fixed angle of incidence will be presented. A novel SPRi method that enables one to perform reproducible quantitative kinetic measurements will be introduced, along with experimental examples of the use of this technique. [Preview Abstract] |
Friday, March 20, 2009 9:48AM - 10:00AM |
Y19.00010: Pentacene on Cu(911): A Density Functional Theory study Abdelkader Kara I use density functional theory to calculate the adsorption energies, geometric and electronic structures of pentacene (C$_{22}$H$_{14})$ on the Cu(911) vicinal surface. The pentacene molecule is found to adsorb nearly flat (slightly arched at the edges) on top of the terrace but close to the step with an adsorption energy of 1.3 eV. The adsorption geometry on Cu(911) is found to differ from that of on Cu(110); but there is a strong bonding between the center carbon atoms of the molecule and Cu atoms near the step. In accord with experimental observations, the arched geometry induces brightness at the edges of the molecule in the STM images. The alignments of the energy levels at the interface induce a change in the work function of about -0.4 eV, in qualitative agreement with the observed -0.9 eV, which is an indication of charge transfer from the molecule to the surface. The details of the electronic structure at the interface will be presented. [Preview Abstract] |
Friday, March 20, 2009 10:00AM - 10:12AM |
Y19.00011: Dynamics within alkylsiloxane SAMs studied by sensitive dielectric spectroscopy Mary Scott, Derrick Stevens, Jason Bochinski, Laura Clarke Self assembled monolayers (SAMs) are a ubiquitous tool in modern research and their static structure has been extensively studied. Fewer investigations have addressed dynamics within these systems; however, such motions within SAMs will affect surface properties such as friction and blocking ability (permeability). In this study, sensitive, dielectric spectroscopy over a broad temperature range (4-400 K) has been employed to study relaxations within planar alkylsiloxane SAMs[1] . Highly disordered SAMs of varying density were grown by vapor deposition. Two dielectric relaxations were observed. The first, a polyethylene-like relaxation similar to that previously reported in phase-segregated alkyl side-chain polymers, is observed for all films with alkyl chains containing four or more carbons. This is an interacting or glassy relaxation. The second motion, which is observable only at high film densities, is a local mode, which follows an Arrhenius dependence on temperature, and has been previously assigned to a sub-chain rotation. [1] M.C. Scott, D.R. Stevens, J.R. Bochinski, L.I. Clarke, ACS Nano. DOI: 10.1021/nn800543j. [Preview Abstract] |
Friday, March 20, 2009 10:12AM - 10:24AM |
Y19.00012: Control of The Morphology of Super-Hydrophobic Surfaces Robert Weiss, Andrey Dobrynin, Xueyuan Wang Textured surfaces consisting of nanometer to micrometer-sized polymer particles were prepared by rapid evaporation of the solvent for a dilute polymer solution. The size and supermolecular structure of the particles and particle aggregates was controlled by the rate of the solvent evaporation. The process is believed to be a spinodal decomposition of the polymer film during casting and the morphology is dictated by pinning the spinodal decomposition process. The surfaces exhibit high water contact angles greater than 150 degrees, making them candidates for applications requiring super-hydrophobicity. [Preview Abstract] |
Friday, March 20, 2009 10:24AM - 10:36AM |
Y19.00013: Biomimetic and responsive artificial surfaces that quantitatively reproduce the water repellency of a Lotus leaf Spiros H. Anastasiadis, Vassilia Zorba, Emmanuel Stratakis, Marios Barberoglou, Emmanuel Spanakis, Panagiotis Tzanetakis, Costas Fotakis, Anca Mateescu, Maria Vamvakaki We report an efficient method for preparing superhydrophobic and highly water repellent surfaces by irradiating silicon wafers with femtosecond laser pulses and subsequently coating them with alkylsilanes or polymer brushes. Such surfaces exhibit controlled dual-scale roughness at the micro- and the nano-scale and water contact angle properties very similar to those of the Lotus leaf. The water repellency of the artificial surfaces is quantified by studying the restitution coefficient of water droplets bouncing off the surfaces as a function of the droplet impact velocity; this is the first time such a direct comparison of performance is made and it clearly demonstrates the possibility of designing highly efficient biomimetic water repellent surfaces. When a polymer brush is ``grafted from'' these surfaces based on a pH-sensitive polymer, these artificially structured surfaces can alter their behavior from super-hydrophilic (after immersion in a low pH buffer) to super-hydrophobic and water-repellent (following immersion to a high pH buffer). Sponsored by NATO's Scientific Affairs Division, by the Greek GSRT and by the EU. [Preview Abstract] |
Friday, March 20, 2009 10:36AM - 10:48AM |
Y19.00014: Haloform Adsorption on Crystalline Copolymers of Vinylidene Fluoride with Trifluoroethylene Carolina C. Ilie, Jie Xiao, Peter A. Dowben Bromoform absorption on crystalline polyvinylidene fluoride with trifluoroethylene, P(VDF-TrFE 70:30) was investigated by photoemission and inverse photoemission and found to be associative and reversible. Molecular bromoform adsorption appears to be an activated process at 120 K with enhanced adsorption following the initial adsorption of bromoform. Strong intermolecular interactions are also implicated in the presence of a weak shake off or screened photoemission final state, whose intensity scales with the unscreened photoemission final state. [Preview Abstract] |
Friday, March 20, 2009 10:48AM - 11:00AM |
Y19.00015: Shear-controlled Micro-nano Scaled Super-Hydrophobic Surfaces with Tunable Sliding Angles from isotactic-Polypropylene / Polypropylene Chlorid Blend Xia Dong, Charles C. Han, Song Hong, Yonghua Yao With proper selection of shear and thermal conditions, super- hydrophobic polymeric surfaces (Contact angle higher than 150$^{\circ}$) with tunable sliding angles (From less than 1$^{\circ}$ to higher than 90$^{\circ}$) can be prepared from isotactic polypropylene (iPP)/ polypropylene chloride (PPC) blend under ambient atmosphere. No further modification with low-surface-energy component is needed. The formed surfaces have good thermal property, chemical and moisture resistance and potentially low manufacturing cost. [Preview Abstract] |
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