Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session B28: Polymer Surfaces II |
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Sponsoring Units: DPOLY Chair: Steve Hudson, NIST Room: LACC 506 |
Monday, March 21, 2005 11:15AM - 11:27AM |
B28.00001: Combined theoretical formulation of Energetic and Entropic driving forces of polymers towards surfaces and comparison with experiments Venkat Minnikanti, Lynden Archer An analytical comparison of the energetic attraction of a polymer towards a surface with entropic driving forces of a polymer has been elusive in the field of surface enrichment of polymers at surfaces. The prediction of crossover molecular weights for surface enrichment of polymers in blends, wherein the dominant of the above mentioned effects is reversed have been restricted to computer simulations in the past. Here we will provide a simple linear response theory that will compare these effects as competitive driving forces towards a surface. Predictions will be made using this theory for the cross over molecular weights and the analysis is extended for polymers of branched architectures. Comparisons of this theory with experiments involving star-linear blends of polybutadienes as well as with lattice simulations will be presented. [Preview Abstract] |
Monday, March 21, 2005 11:27AM - 11:39AM |
B28.00002: Formation and Properties of Molecular Loops at Polymeric Interfaces J. Kevin Rice, Mark Dadmun, Brandon Farmer, Haining Ji, Jimmy Mays In this study, we investigate the formation, kinetics, and resultant strength improvements of multiply bound polymer loops at multicomponent polymeric interfaces. We have first studied a model system consisting of a silicon substrate, an epoxy terminated monolayer, and dicarboxy terminated polystyrene to characterize the formation of the surface bound molecular loops. Interfacial strength improvement via loop formation in this model system has also been investigated using asymmetric double cantilever beam (ADCB) analysis. Further, the kinetics of loop formation at a soft interface between polystyrene and poly(methyl methacrylate) has been investigated with neutron reflectivity. This data will then be used to apply the technique to a range of real systems, such as layered-silicate or carbon nanotube filled polymeric systems, with the goal of improving dispersion and desired property enhancement within these systems. [Preview Abstract] |
Monday, March 21, 2005 11:39AM - 11:51AM |
B28.00003: Interfacial Segregation Driven by Architectural Asymmetry in Blends of Branched and Linear Polymers Jae S. Lee, Nam-heui Lee, Alexei P. Sokolov, Roderic P. Quirk, Mark D. Foster, Charles F. Majkrzak The effects of the number of branch points and number of chain ends in a branched chain on interfacial segregation in binary blends of well-defined, regularly branched polystyrenes with their linear analogues were studied using Neutron Reflectometry (NR) and Surface-Enhanced Raman Spectrometry (SERS). A novel series of molecules in which the number of branch points in the molecule was varied from 1 to 2 to 4 while keeping the number of chain ends fixed at 6 enabled an incisive look at the branch point effects. Similarly, a novel series of molecules in which the number of branch points in each molecule was fixed at 4 and the number of chain ends varied among 6, 9, and 15 provided the opportunity to focus on end effects. The branched molecules segregate preferentially to both interfaces of blend films. The strength of the segregation generally increases when increasing the number of branch points while the number of end groups is kept at six. The degree of segregation also increases when increasing the number of end groups while keeping the number of branch points constant at four. [Preview Abstract] |
Monday, March 21, 2005 11:51AM - 12:03PM |
B28.00004: Effect of sequence distribution on copolymer interfacial activity Michelle D. Lefebvre, Rachel L. McSwain, Christine M. Dettmer, Jonathan R. Davila, SonBinh T. Nguyen, Kenneth R. Shull, Chen Xu, Russell J. Composto Interfacial segregation of diblock, gradient, and random copolymers was measured using forward recoil spectrometry. The norbornene-based polymers were synthesized using a ring-opening metathesis polymerization, allowing control over the sequence distribution. Mean field theory accurately describes the distinction between interfacial segregation and the formation of an interfacial wetting layer, but quantitative predictions are complicated for copolymers with a large gradient because of intermolecular variations in the sequence distribution. [Preview Abstract] |
Monday, March 21, 2005 12:03PM - 12:15PM |
B28.00005: Towards a Universal Profile for Polymer Brushes: Effect of Surface Heterogeneity on Brush Structure S. Michael Kilbey, II, Peng Tian, Hiroshi Watanabe Amphiphilic block copolymers can be preferentially assembled at the solid-fluid interface to form polymer brushes. Brushes are of interest because they can mediate interactions across interfaces and confer desirable properties to the underlying surface. Using the surface forces apparatus, we have studied the forces of interaction between opposing brushes made from comb and mikto-arm copolymers (made of polystyrene/polyvinylpyridine and polystyrene/polyisoprene copolymers) as these layers are brought into and out of molecular level contact. The brushes formed from these branched polymer amphiphiles display an additional repulsion due to local effects (branching) and anchor block heterogeneity. We will describe how we have used these results on branched brushes and their linear analogs to develop a predictive universal profile based on a mean field description of the brush that properly scales the dependence of the force of interaction on molecular weight, tethering density, segment size, branching, solvent quality, and surface heterogeneity. [Preview Abstract] |
Monday, March 21, 2005 12:15PM - 12:27PM |
B28.00006: Computational Modeling of the Temperature-Induced Structural Changes of Tethered Poly(N-isopropylacrylamide) John G. Curro, Sergio Mendez, John D. McCoy, Gabriel P. Lopez We modeled the effects of temperature, degree of polymerization, and surface coverage on the equilibrium structure of tethered Poly(N- isopropyl acrylamide) chains immersed in water. We employed a numerical self-consistent field theory where the experimental phase diagram was used as input to the theory. At low temperatures, the composition profiles are approximately parabolic and extend into the solvent. By contrast, at temperatures above the LCST of the bulk solution, the polymer profiles are collapsed near the surface. The layer thickness, and the effective monomer fraction within the layer, undergo what appears to be a first-order change at a temperature that depends on surface coverage and chain length. Our results suggest that as a result of the tethering constraint, the phase diagram becomes distorted relative to the bulk polymer solution and exhibits closed loop behavior. [Preview Abstract] |
Monday, March 21, 2005 12:27PM - 12:39PM |
B28.00007: Random Copolymer Brushes on Silicon Carbide William Gibson, Jeremy Jarl, Eric Botello, Elizabeth Covington, Phillip Hartnet, Deborah Koeck, David Donnelly, Heather Galloway, Suresh Murugesan, Gary Beall, Chad Booth, Patrick Cassidy We are investigating the deposition of ordered films of diblock copolymers onto semiconductor substrates. These surfaces require a non-preferential surface to allow the ordering of the diblock material. The literature$^{[1,2]}$ available on the deposition of random copolymers (RCP) on silicon describes anneal times ranging from one to three days. We are interested in closer study of the necessary anneal time and of extending the use of RCP onto an amorphous SiC layer on silicon. We found a minimum anneal time and look at the significance of cooling method on the bonding/surface conditions of the RCP. We compared rinse methods post anneal. The analysis is accomplished using Fourier Transform Infrared Spectroscopy and Atomic Force Microscopy. [1] P. Mansky, Y. Liu, E. Haung, T. P. Russell, C. J. Hawker, \textit{Science}, 275, 1458, 1997 [2] Ting Xu, Ho-Cheol Kim, Jason Derouchey, Chevey Seney, Catherine Levesque, Paul Martin, C. M. Stafford, T.P. Russell, \textit{Polymer} 42, 9091, 2001 [Preview Abstract] |
Monday, March 21, 2005 12:39PM - 12:51PM |
B28.00008: Interface Roughness Correlations and Surface Fluctuations in Diblock Copolymer Brushes Synthesized by Atom Transfer Radical Polymerization Mark D. Foster, Bulent Akgun, William J. Brittain, Jin Wang, Xuefa Li Correlation between the interior interface and air surface of a diblock brush has been detected using longitudinal diffuse X-ray scattering and specular X-ray reflectivity. Polystyrene-b-polymethacrylate brushes were synthesized by sequential polymerization of first polystyrene and then polymethylacrylate using Atom Transfer Radical Polymerization. The amplitude of the fringes in the longitudinal diffuse scattering decreases with increasing thickness of the polymer brush, indicating the interactions between substrate and brush surface decrease as the thickness of the layers increases. Correlation of the roughnesses of the top and bottom interfaces of the brush is observed after annealing the brush at a temperature above the glass transition temperatures of both polymers. This correlation is lost after the brush is swollen in the vapor of a nonselective solvent, dichloromethane. Transverse diffuse X-ray scattering measurements have shown that long wavelength fluctuations are suppressed at the air interface. [Preview Abstract] |
Monday, March 21, 2005 12:51PM - 1:03PM |
B28.00009: Nested self-similar wrinkling patterns in skins Kirill Efimenko, Jan Genzer, Mindaugas Rackaitis, Evangelos Manias, Ashkan Vaziri, L. Mahadevan We describe a simple method for generating topographically corrugated elastomeric surfaces comprising multidimensional cascades of wrinkles. These wrinkled surfaces are generated by uniaxially stretching silicon elastomer films, exposing their surfaces to prolonged ultraviolet/ozone treatment and releasing the initial strain imposed on the specimens. We show that such elastomeric artificial skins wrinkle in a hierarchical pattern consisting of self-similar buckles extending over five orders of magnitude in length scale, ranging from a few nanometers to a few millimeters. We provide a mechanism for the formation of this hierarchical wrinkling pattern, and quantify our experimental findings with both comparative computations and a simple scaling theory. Understanding the wrinkle-forming mechanism allows us to harness the substrates for applications. In particular, we show how to utilize the multigeneration-wrinkled substrate for separating particles based on their size, while simultaneously forming linear chains of equisized particles. [Preview Abstract] |
Monday, March 21, 2005 1:03PM - 1:15PM |
B28.00010: Interaction of Peo-Ppo-Peo Block Copolymer with Model Lipid Membranes Guohui Wu, Jaroslaw Majewski, Canay Ege, Kristian Kjaer, Markus Weygand, Jyostana Lal, Ka Yee C. Lee The interactions between Poloxamers (nonionic PEO-PPO-PEO copolymers), known to seal damaged membranes, with phospholipids monolayers and bilayers are documented based on x-ray and neutron scatterings. X-ray reflectivity and grazing incidence diffraction on the molecular structure of lipid/poloxamer thin film at air/water interface reveal the effect of poloxamer on lipid ordering and the location of P188 in the lipid matrix. P188 \textit{selectively }inserts into low lipid-density regions of the membrane and ``corrals'' lipid molecules to pack tightly, leading to unexpected Bragg peaks at low nominal lipid density and inducing lipid/poloxamer phase separation. At tighter lipid packing, the once inserted P188 is squeezed out, allowing the poloxamer to gracefully exit when the membrane integrity is restored. The confirmational change of poloxamer in solution induced by lipid bilayer are observed with neutron reflectivity (supported bilayer) and small angle neutron scattering (unilamellar vesicles). [Preview Abstract] |
Monday, March 21, 2005 1:15PM - 1:27PM |
B28.00011: Detection of a thin depletion region of water on an extended hydrophobic surface using x-ray reflectivity Andrew Richter, Jason Van de Walker What happens when water is placed on top of a hydrophobic surface? On the molecular level the picture is not yet clear. Further exploration of the hydrophobic effect is necessary to understand protein folding, fluid flow, and the attractive force between two closely positioned hydrophobic surfaces in the presence of water. Researchers have begun to probe this important interface using a variety of methods, finding phenomena ranging from the formation of nanobubbles to the presence of a thin vacuum layer to the absence of any effect at all. Using the technique of x-ray reflectivity at the interface between water and a hydrophobic self-assembled monolayer, we have detected the presence of a thin depletion region and quantified its characteristics. The depleted region has a density of about two-thirds that of bulk water and extends over approximately 0.3-0.6 nm, a figure much closer to the theoretically predicted value than seen using other methods [1]. We will present these findings as well as those from experiments that used other liquids. [1] Lum, K. \textit{et al}., \textit{J. Phys. Chem. B} \textbf{103}, 4570-4577 (1999). [Preview Abstract] |
Monday, March 21, 2005 1:27PM - 1:39PM |
B28.00012: Structure and electrical property of DNA molecules immobilized on the patterned self-assembled monolayers Yoichi Otsuka, Kaoru Ojima, Takuya Matsumoto, Hitoshi Tabata, Tomoji Kawai In spite of studies of the electrical property of DNA, results are controversial yet. This is because many factors are involved in sample preparation processes and/or measurement procedures that affect the electrical property. One of the important factors is the structure. As DNA molecules are flexible, they are bent easily on the solid surface. The bending results in losing of pi-stack and conductivity. We have prepared the substrate patterned with hydrophilic and hydrophobic surface by the radiation of deep UV to self-assembled monolayers (trimethoxypropylsilane) on the silicon oxide through the lithographic mask. After the immobilization of lambda DNA on the patterned substrate, we have found that DNA molecules are randomly immobilized on the hydrophilic area. On the other hand, DNA molecules are bundled, stretched and aligned in the direction of nitrogen gas flow on the hydrophobic area. Moreover, nanogap electrodes are fabricated on the samples by the angle-controlled thermal deposition method [\textit{Nanotechnology} \textbf{15, }1639 (2004).], in order to avoid the structural deformation at the edge of the electrodes, and electrical conductivity is measured. [Preview Abstract] |
Monday, March 21, 2005 1:39PM - 1:51PM |
B28.00013: Liquid crystals alignments on heterogeneous surfaces Jones Tsz-Kai Wan, Ophelia Tsui, Ping Sheng, Hoi-Sing Kwok The effects of a nonuniform surface on the director field of a nematic liquid crystal (LC) is studied by computer simulations. The nonuniform surface is made by mixing a homeotropic anchoring domain and a planar anchoring domain with different area fractions. For each area fraction, a dimensionless parameter is derived to simultaneously study the geometric and the material effects on the director field. In the limit of weak anchoring, the average pretilt angle can be expressed analytically in terms of the area fractions of the anchoring domains. When in the strong anchoring limit the average pretilt angle varies with the area fractions almost linearly and is independent of the geometric and material parameters. The results are confirmed by computer simulations. [Preview Abstract] |
Monday, March 21, 2005 1:51PM - 2:03PM |
B28.00014: Switchable Adhesion from Bicomponent Polymeric Brushes Haris Retsos, Ganna Gorodyska, Anton Kiriy, Mandred Stamm, Costantino Creton We investigated the adhesive and wetting properties of bicomponent polymeric brushes made from end functionalized hydrophilic and hydrophobic polymer chains. The molecular organization of the mixed brush could be varied reversibly by exposure to selective solvents for the two polymers. Adhesive properties were tested by debonding a flat ended probe from soft pressure-sensitive-adhesives (hydrophobic {\&} hydrophilic) and wetting properties were tested by contact angle measurements of water {\&} diiodomethane droplets. The bicomponent brushes were chemically grafted on silicon wafers from end-functionalized chains. Wetting experiments were done directly on the wafers while for adhesion experiments, the wafers were glued on the flat end of the probe prior to the tests. In all cases the organization of the bicomponent brush could be modified reproducibly and reversibly by exposure to selective solvents. Following this strategy we succeeded to create remarkably stable adaptive polymer surfaces that can modify their adhesion and wetting reversibly and also tune them by varying the ratio of the bicomponent brush layer. [Preview Abstract] |
Monday, March 21, 2005 2:03PM - 2:15PM |
B28.00015: Template-Induced Enhanced Ordering under Confinement Betul Yurdumakan, Kumar Nanjundiah, Gary Harp, Ali Dhinojwala We report a direct observation of a confined structure between two surfaces, oxidized poly(dimethylsiloxane) (PDMS$^{ox})$ elastomer and methyl terminated self-assembled monolayer (OTS) on sapphire substrates, using sum frequency generation spectroscopy. The Si--(CH3)2 groups of short PDMS chains at this interface exhibit a surprisingly strong order upon confinement that is comparable to that of a well packed OTS. This enhanced ordering is induced by the template of ordered methyl groups of OTS and is not observed for other surfaces (fluorinated monolayers and sapphire substrates). This strong ordering is reminiscent of layering observed for confined symmetric molecules between two mica surfaces, but was expected to vanish between rough macroscopic surfaces. Friction and adhesion properties of the same interface are evaluated with a sliding contact and JKR technique, respectively. These results provide new insights on confined structure at the interface between two solids and are important in the understanding of surface controlled processes of practical importance such as friction and adhesion. [Preview Abstract] |
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B28.00016: Correlation Between Interfacial Mositure Content and Adhesive Fracture Energy Emmett O'Brien, Bryan Vogt, Christopher White The effect of surface chemistry and moisture on adhesion was investigated using neutron reflectivity and the shaft-loaded blister test. Four different surface treatments were examined: bare Al$_2$O$_3$, t-butylphosphonic acid, phenyl phosphonic acid, and n-octyltrichlorosilane. Measurements were taken in the dry condition and after samples were equilibrated in a 100{\%} relative humidity. Previous neutron reflectivity work by Vogt (submitted to Macromolecules) on spincoated films of poly(4-tert-butoxycarbonyl-oxystyrene) has shown that the phenyl and octyl surface treatments reduced the amount of water at the interface, relative to the bare aluminum. The t-butyl treatment did not reduce the interfacial moisture content. These results were correlated to adhesive fracture energy measurement of spin coated PMMA films. The adhesion measurements match the expected trend. The phenyl surface had the largest adhesion strength and a low interfacial moisture content. The t-buty and bare Al$_2$O$_3$ surface had similar moisture contents and adhesion energy. The octyl treated surface had the worst adhesion but the lowest interfacial moisture content. [Preview Abstract] |
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