Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session B17: Surfaces, Interfaces and Thin Films |
Hide Abstracts |
Sponsoring Units: DPOLY Chair: Jutta Luettmer-Strathmann, University of Akron Room: B116 |
Monday, March 15, 2010 11:15AM - 11:27AM |
B17.00001: Monte Carlo Simulation of the Irreversible Adsorption of Polymers to Surfaces: Influence of Molecular Weight Vikram Kuppa Monte Carlo simulations using a coarse-grained, freely rotating chain model are employed to investigate the behavior of linear polymer chains whose constituent beads are attracted to flat, perfectly smooth surfaces by interactions much stronger than thermal energy, kT. We investigate the effect of chain molecular weights on such a system by conducting the simulations in an ensemble which provides control over the chain lengths by allowing the exchange of monomer beads between different chains. The structure of the adsorbed polymer layers is characterized by monomer density profiles, bond order parameters, fractions of adsorbed monomers per chain, and populations of tails, loops and trains. Systems in which polymer lengths are constrained to a narrow range show pronounced and structured density profiles as compared to those in which a distribution of chain molecular weights is permitted to exist. The adsorbed bead fraction shows a broad distribution only for the narrow molecular weight case, indicating that the competition amongst chains to make contact with the surface is modified by the population of chain lengths. Our results are derived in the context of varying interaction strengths, molecular weight distributions, segregation effects, and interacting monomer sequences. [Preview Abstract] |
Monday, March 15, 2010 11:27AM - 11:39AM |
B17.00002: Probing Aggrecan Interactions with Ions by AFM Preethi Chandran, Emilios Dimitriadis, Peter Basser, Ferenc Horkay Aggrecan (MW $\cong $2 MDa) is a highly charged bottle-brush shape biological polymer found in the extracellular matrix of tissues. It consists of a protein backbone ($\cong $400nm long), to which about 100 linear chains of negatively-charged glucosaminoglycans are attached approximately 4 nm apart. The high charge density of the aggrecan bottle-brush allows it to imbibe water, thereby maintaining tissue hydration and permeability, while also binding to cell-signaling molecules. In solution, aggrecan molecules respond differently to varying salt conditions, than other charged biological and synthetic polyelectrolytes like DNA and poly(acrylic acid) (Horkay, 2008). To probe the nature of its interactions with charged surfaces, we looked at the absorption patterns of aggrecan assemblies on controlled surfaces (polylysine, mica) under different ionic conditions, using Atomic Force Microscopy. We propose a simple model of the charge interactions, which relates the surface-adsorption patterns to the solution structures. The study may help understanding how aggrecan loss or degradation with age and joint disease affects tissue microstructure and physical properties. [Preview Abstract] |
Monday, March 15, 2010 11:39AM - 11:51AM |
B17.00003: Polyelectrolyte adsorption at a conducting surface Maria Sammalkorpi, Paul R. Van Tassel Polyelectrolyte films are useful as separation membranes and sensor substrates, and are usually grown as multilayer assemblies of oppositely charged layers because single layer adsorption quickly saturates due to interfacial charge build-up. In recent experiments, we have observed polyelectrolyte adsorption to a conducting surface to become continuous, i.e., linear with time over hours. This discovery offers an enticing possibility of nanoscale thin film growth in a single step process, but also opens questions of the underlying mechanisms. Three key features to the process may be polymer charge regulation, the dielectric discontinuity at the adsorption surface, and short-range attractive interactions of the polymers. Here we present a molecular simulation study aimed at understanding the continuous adsorption process in terms of these features, and reveal conditions where they together lead to stable polymer-polymer binding and continuous adsorption on a conducting surface. Additionally, we discuss the effects of ion-ion correlations in light of recent experimental observations. [Preview Abstract] |
Monday, March 15, 2010 11:51AM - 12:03PM |
B17.00004: Temperature Dependent Micellization of Polystyrene-$b$-poly(2-vinylpyridine) at Si--Ionic Liquid Interface Haiyun Lu, Thomas Russell Highly ordered and stable surface micelles formed from both symmetric and asymmetric block copolymers of polystyrene-$b$-poly(2-vinylpyridine) (PS-$b$-P2VP) at the Si-ionic liquid (IL) interface have been investigated. The 1-butyl-3-methylimidazolium trifluoromethanesulfonate IL, a selective and temperature-tunable solvent for P2VP, was used and gave rise to block copolymer micelles having different morphologies that strongly depended on temperatures. In addition, the micellar structures formed also depended on the film thickness, molecular weight of polymers, substrate and experimental conditions such as pre-annealing, rinsing, and interaction time. The possible mechanism for micelle formation will be discussed. [Preview Abstract] |
Monday, March 15, 2010 12:03PM - 12:15PM |
B17.00005: Modeling Micellization and Interfacial Tension of Nonionic Surfactants using Dissipative Particle Dynamics Leela Rakesh, Valeriy Ginzburg, Prasanna Jog We use Dissipative Particle Dynamics (DPD) to simulate thermodynamic behavior of nonionic surfactants. In particular, we study the micellization of linear alkylethoxylates (CH$_{3}$-[CH$_{2}$]$_{n-1}$-O-[CH$_{2}$-CH$_{2}$-O]$_{m}$H or C$_{n}$E$_{m)}$ in water, as well as the influence of these surfactants on the oil-water interfacial tension. We demonstrate that for surfactants with n = 6, the onset of micellization in water occurs when the total surfactant concentration is on the order of 1{\%}, in agreement with experimental data and Quantitative Structure-Property Relationship (QSPR) models. We also simulate the dependence of dynamic and equilibrium interfacial tension in water/hexadecane/surfactant ternary mixture on the surfactant concentration and investigate the influence of micelle formation on the interfacial tension. [Preview Abstract] |
Monday, March 15, 2010 12:15PM - 12:27PM |
B17.00006: Self-assembly of ultrahigh molecular weight comb block copolymer at the air/water interface Lei Zhao, Matthew Goodman, Ned Bowden, Zhiqun Lin Self-assembly of a newly synthesized, amphiphilic comb block copolymer (CBCP) at the air/water interface was systematically explored using the Langmuir Blodgett (LB) technique. The CBCP had an ultra high molecular weight (MW = 510 x 10$^{3}$ g/mol) with polystyrene arms grafted along one block of long hydrophilic backbone. At the air/water interface, the CBCP molecules spontaneously assembled into ribbon-like structures and cellular patterns at the zero surface pressure when volatile solvent (i.e., chloroform) and less volatile solvent (i.e., toluene) were used, respectively. This spontaneous self-assembly behavior of CBCP was induced by the dewetting process. The mechanism for the morphological change as a function of surface pressure was scrutinized and further confirmed by the compression-expansion cycle and solvent vapor annealing studies. To the best of our knowledge, this is the \textit{first study} of self-assembly of ultrahigh MW, amphiphilic CBCP at the air/water interface. As such, it provides insight into the design of controllable pattern formation using amphiphilic copolymers. [Preview Abstract] |
Monday, March 15, 2010 12:27PM - 12:39PM |
B17.00007: Formation and Collapse of Single-Monomer-Thick Monolayers of Poly(n-Butyl Acrylate) at the Air-Water Interface You-Yeon Won, Kevin Witte, Wei Sun, Sumit Kewalramani, Masafumi Fukuto, Ivan Kuzmenko The behavior of poly($n$-butyl acrylate) (PnBA) spread at the air-water interface has been studied for a full range of surface coverages. Beginning in the concentrated regime, and through the full coverage regime, x-ray reflectivity measurements show the formation of a continuous water-free one-monomer-thick film of the polymer. At surface concentrations above the transition point to the full coverage regime, Brewster angle microscopy shows that the excess polymer material does not distribute uniformly in the polymer film layer but instead leads to formation of micrometer-scale isolated globular domains. Further, the number of such domains increases as the surface polymer concentration is increased, whereas the size of the domains is unaffected by the concentration variation. X-ray grazing incidence diffraction indicates that these domains are regions of bulk-like polymer. We speculate that the globular domains are formed as a result of the interplay between the entropic tendency of the excess PnBA chains to create as many small domains as possible and the energetic penalty associated with the creation of additional polymer-water interfaces. A simple theoretical model based on this picture will be presented and used as a basis for discussion of the experimental observations. [Preview Abstract] |
Monday, March 15, 2010 12:39PM - 12:51PM |
B17.00008: The Interactions of Surface Hydroxyl Groups on Sapphire with Hydrophobic and Hydrophilic Polymers Anish Kurian, Shishir Prasad, Ali Dhinojwala We have studied the buried interface between sapphire and various hydrophobic and hydrophilic polymers using infrared-visible sum frequency generation spectroscopy. We have observed a free hydroxyl peak on sapphire surface between 3550 and 3720 cm-1. The peak position of the surface hydroxyl peak is strongly affected by the orientation and interaction of the polar groups of the polymers with the sapphire surface OH groups. These interfacial interactions have important consequences on wetting, adhesion and friction. [Preview Abstract] |
Monday, March 15, 2010 12:51PM - 1:03PM |
B17.00009: Surfaces and polymers: The dynamics of intimacy Subhalakshmi Kumar, Changqian Yu, Janet Wong, Liang Hong, Sung Chul Bae, Steve Granick The dynamics of a hydrophobic polymer melt, well above its glass transition, is probed when it is confined to~thicknesses of a few nanometers. The ability of the surface forces apparatus to produce controlled thin films is coupled with measurements using fluorescence recovery after photobleaching technique. Insight into the effects of degree of confinement on diffusion of the polymer molecules and heterogeneity in their dynamic behavior is sought. [Preview Abstract] |
Monday, March 15, 2010 1:03PM - 1:15PM |
B17.00010: Thickness-Dependent Surfactant Behavior in Trilayer Polymer Films Yan Sun, Kenneth Shull, Jin Wang The ability for thin liquid films to wet and remain thermodynamically stable on top of one another is a fundamental challenge in developing high quality paints, coatings, adhesives, and other industrial products. Since intermolecular interactions and interfacial energies dominate in the film thickness regime from tens to hundreds of nanometers, it is desirable to tune these long-range and short-range forces in a simple, controllable manner. Starting from an unstable model homopolymer bilayer (poly(styrene)/poly(4-vinylpyridine)), we demonstrate that sandwiching an additional homopolymer layer (poly(4-bromostyrene)) between the two layers can provide needed surfactancy. As the thickness of this center layer is increased, the full trilayer transitions from unstable (thin) to stable (moderate) to unstable (thick). We experimentally show using x-ray standing waves generated via total external reflection (TER-XSW), atomic force microscopy (AFM), and time-of-flight secondary ion mass spectroscopy (ToF-SIMS) that this behavior can be directly attributed to the autophobic dewetting phenomenon, in which the surfactant layer is thin enough to remain stable but thick enough to shield the neighboring layers, highlighting a general approach to stabilizing multilayer systems. [Preview Abstract] |
Monday, March 15, 2010 1:15PM - 1:27PM |
B17.00011: Plateau-Rayleigh instability in nanoscale polymer rings Kari Dalnoki-Veress, Joshua McGraw, Jianfeng Li, David Tran, An-Chang Shi A liquid jet can break up into a stream of droplets as a result of the Plateau-Rayleigh instability. Droplet formation decreases the jet's surface area and hence its free energy. Here we present the results of experiments in an unconventional geometry where this instability can be observed: toroidal sections. We discuss the formation of toroidal polystyrene with nanometer length scales. The constraints imposed by this geometry affect its observed instability in comparison to a simple linear jet. Specifically,the curvature imposed by the ring plays a crucial role in the energy minimization route. [Preview Abstract] |
Monday, March 15, 2010 1:27PM - 1:39PM |
B17.00012: Morphology of Block Copolymer Droplets on a Flat Substrate Jaeup Kim, Mark Matsen We study the equilibrium morphology of a droplet of symmetric AB diblock copolymer on a flat substrate. A previous experiment [A. B. Croll et al. {\it Phys. Rev. Lett.}, {\bf 97}, 204502 (2006)] has reported conical-shaped droplets with a terraced surface. Using self-consistent field theory (SCFT), we provide the first predictions for the equilibrium droplet shape and its internal structure. When the substrate affinity for the A component, $\eta_A$, is small, the droplet adopts a nearly spherical shape much like that of simple fluids. Inside the spherical droplet, however, the block copolymer molecules acquire an ordered morphology consisting of concentric circular lamellar layers stacked on top of each other; hence the thickness of the droplet is effectively quantized by a half-integer or integer number of layers. At larger $\eta_A$ and smaller contact angle, the area of the upper-most layer becomes relatively large resulting in a nearly flat, faceted top surface, followed by a semi-spherical slope. This geometry is remarkably reminiscent of the droplet shapes observed for smectic liquid crystals. [Preview Abstract] |
Monday, March 15, 2010 1:39PM - 1:51PM |
B17.00013: Response of Semifluorinated-Si Containing Diblock Co-polymers to Solvent Stimuli Umesh Shrestha, Dvora Perahia, Stephen Clarson The response of semifluorinated diblock co-polymers to solvents has been studied by neutron reflectometry. Polytrifluoro propyl methyl siloxane -$b$- polystyrene (FSi-PS) with different volume fraction of the fluorinated block ranging from 0.03 to 0.5 were exposed to water and toluene as stimuli. FSi-PS segregated into layers with the air interface being fluorine rich. Upon exposure to water as stimuli, at small volume fractions of the FSi, no response was observed. Increasing the size of the FSi segments resulted in small interfacial rearrangements however no swelling was observed. The small interfacial changes are sufficient to affect the surface energy and adhesion of the diblocks as desired of a responsive interface. Changing the nature of the stimuli to toluene, which is a good solvent for polystyrene, the diblock co-polymer swelled almost immediately independent on the volume fraction, though the inherent layered structure was retained. The degree of fluorine that resides at the interface in this case depends on the volume fraction and the exposure time. Over all, the study has shown that internal segregation of the blocks and their distinct different affinities to the solvents provide the driving forces for their response. [Preview Abstract] |
Monday, March 15, 2010 1:51PM - 2:03PM |
B17.00014: Temperature-Induced, Reversible Swelling Transitions in Multilayers of a Cationic Triblock Copolymer and a Polyacid Svetlana Sukhishvili, Wui Siew Tan, Robert Cohen, Michael Rubner We demonstrate large-scale, fully-reversible, thermally-induced volumetric changes in layer-by-layer (LbL) electrostatically self-assembled thin films through the incorporation of A-B-A triblock copolymers, where A is a weak polyelectrolyte block, and B is a temperature-responsive block. Multilayers of a micelle-forming A-B-A triblock copolymer were constructed using LbL deposition with a polyanion. The polyanion type and self-assembly pH were critical parameters for constructing functional films of block copolymer micelles (BCMs). When a polycarboxylic acid was used in self-assembly, films assembled at pH $\ge $ 6 showed fully reversible, 3 to 5-fold changes in film thickness in response to temperature cycling between 6 and 20 $^{\circ}$C, enabled by swelling/collapse of the BCM central block. [Preview Abstract] |
Monday, March 15, 2010 2:03PM - 2:15PM |
B17.00015: Van der Waals model for phase transitions in thermoresponsive surface films John McCoy, John Curro Phase transitions in polymeric surface films are studied with a simple model based on the van der Waals equation of state. Each chain is modeled by a single bead attached to the surface by an entropic-Hooke's law spring. The surface coverage is controlled by adjusting the chemical potential, and the equilibrium density profile is calculated with density functional theory. The interesting feature of this model is the multivalued nature of the density profile seen at low temperature. This van der Waals loop behavior is resolved with a Maxwell construction between a high-density phase near the wall and a low-density phase in a ``vertical'' phase transition. Signatures of the phase transition in experimentally measurable quantities are then found. Numerical calculations are presented for isotherms of surface pressure, for the Poisson ratio, and for the swelling ratio. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700