Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session H18: Block Copolymers in Solution and Blends |
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Sponsoring Units: DPOLY Chair: Ryan Hayward, University of Massachusetts-Amherst Room: Morial Convention Center 210 |
Tuesday, March 11, 2008 8:00AM - 8:36AM |
H18.00001: Polymer Physics Prize Break
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Tuesday, March 11, 2008 8:36AM - 8:48AM |
H18.00002: Competitive Adsorption, Exchange and Binding of Polymers and Proteins at the Oil/Water Interface Daniel Carvajal, Kenneth Shull, Igal Szleifer Drop Shape Analysis (DSA) of pendant drops was used to study competitive adsorption, exchange kinetics and binding of macromolecules at the oil/water interface. Amphiphilic diblock and triblock copolymers were dissolved in the oil drop phase, while proteins were added to the water subphase. By using DSA to monitor the interfacial tension of the system, we were able to gather data on how the polymers and proteins are behaving and interacting at the oil/water interface. Some polymer systems were found to fully inhibit both specific and non-specific adsorption of proteins to the interface. Adding biological receptors to these polymers allowed us to study the specific binding of proteins to polymers located at the interface. In other systems, proteins were able to penetrate the amphiphilic block copolymer layer and reach the interface. The dynamics of exchange and competitive adsorption in these polymer/protein systems were also studied. [Preview Abstract] |
Tuesday, March 11, 2008 8:48AM - 9:00AM |
H18.00003: Interfacial Properties of Semifluorinated Alkane Diblock Copolymers Flint Pierce, Dvora Perahia, Mesfin Tsige, Oleg Borodin, Gary Grest The surface interaction of semifluorinated alkane diblock (SFAs) copolymers with water and normal alkanes are studied using explicit atom molecular dynamics (MD) simulations. At the diblock/air interface, the surface is dominated by fluorinated groups as a result of their low surface tension, and these groups reside at the interface for longer periods of time than the hydrogenated groups. Fluorinating even a single end group on an otherwise hydrogenated chain results in low surface tensions, close to that of perfluoroalkanes and far from normal alkanes. For the interface with water, results for the rate of water uptake by alkanes, perfluoroalkanes, and SFAs will be presented. Additionally, we report the interfacial surface tensions and equilibrium density profiles for these samples, focusing on the prevalence of fluorinated and hydrogenated segments at each interface. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under Contract DE-AC04- 94AL85000. [Preview Abstract] |
Tuesday, March 11, 2008 9:00AM - 9:12AM |
H18.00004: Amphiphilic copolymer assemblies formed by interfacial instabilities of oil-in-water emulsions Jintao Zhu, Ryan C. Hayward Self-assembly of amphiphiles into discrete nano-objects is of fundamental interest and is important for applications including encapsulation and drug delivery. We will describe a new method by which amphiphilic block copolymers can be controllably assembled into hierarchically-structured microparticles and various micellar morphologies. We first form oil-in-water emulsion droplets, where the dispersed phase consists of a volatile organic solvent containing a dilute concentration of amphiphilic polystyrene-block-poly(ethylene oxide) diblock copolymer. Upon extraction of the organic solvent, the droplets undergo interfacial instabilities which lead to formation of microparticles with budding vesicle, foam-like, or dendritic structures, or micelles with spherical, cylindrical, or more complicated morphologies. We will discuss how the structures of these assemblies can be tuned, and the opportunities that they present for encapsulation of hydrophobic species. [Preview Abstract] |
Tuesday, March 11, 2008 9:12AM - 9:24AM |
H18.00005: Helical cylinders or multicompartment cylinders through the solution assembly of charged block copolymers with multivalent organic counterions Darrin Pochan, Sheng Zhong, Honggang Cui, Zhiyun Chen, Karen Wooley By manipulating the interaction of charged block copolymer hydrophilic corona blocks with multivalent organic counterions, and controlling the kinetics of block copolymer solution self-assembly, desired micelle geometries can be formed. Specifically, polyacrylic acid-b-polymethylacrylate-b-polystyrene amphiphilic triblock copolymers were studied in water/THF solvent mixtures with organic multiamines as counterions. By manipulating block copolymer and solvent composition, different micelle geometries were formed. However, by altering the chemical structure and/or concentration of the multiamine counterions, as well as the kinetic pathway through which the molecules are assembled, complex nanostructures were formed. An example of nanostructure from kinetic control includes spherical micelles that can be controllably assembled into 1-d multicompartment cylinders. Examples of nanostructure from control of the type and amount of multivalent organic counterion added are helical cylinder superstructures many micrometers in length. The system has been investigated by means of cryogenic transmission electron microscopy (cryo-TEM) and small angle neutron scattering (SANS). [Preview Abstract] |
Tuesday, March 11, 2008 9:24AM - 9:36AM |
H18.00006: Spotted Polymersomes and Striped Worms - a theoretical analysis of lateral segregation of diblock copolymers Wouter G. Ellenbroek, David A. Christian, Aiwei Tian, Andrea J. Liu, Tobias Baumgart, Dennis E. Discher Lipids and amphiphilic block copolymers are both known to assemble into vesicle and worm-like micelle morphologies, but only mixtures of lipids in vesicles have been directly seen to phase separate into meso-scale lateral domains. Here we show direct visualization of meso-scale spots in tough polymersomes and micron-length stripes in stable worms that result from strong lateral segregation of polyanionic and neutral diblock copolymers. We present a model for understanding the crucial role of calcium ions on segregation behavior, which incorporates counterion condensation and ``crosslinking'' (ion bridging). We find a tendency towards segregation near the isoelectric point as a result of competition among counterion entropy, repulsion due to the net charge, and attraction due to crosslinking. These results portend new classes of robust membranes and cylinders that exhibit lateral patterns at the meso-scale. [Preview Abstract] |
Tuesday, March 11, 2008 9:36AM - 9:48AM |
H18.00007: Pathways of Spontaneous Vesicle Formation of ABA Amphiphilic Molecules in Selective Solvent. Wei Jiang, Hongbo Du We study the pathways of spontaneous vesicle formation of the ABA amphiphilic molecules in selective solvent by Monte Carlo simulation. Simulation results reveal that the pathway for the spontaneous vesicle formation of the amphiphilic molecules in selective solvent depends strongly on the annealing speed. We can not use one pathway model to describe the vesicle formation even though for the same system and condition. Hydrophobic molecules diffusing in spherical micelles and oblate membrane closing may coexist for the vesicle formation. [Preview Abstract] |
Tuesday, March 11, 2008 9:48AM - 10:00AM |
H18.00008: Effects of depletion interactions on block copolymer micelles Sayeed Abbas, Timothy P. Lodge Block copolymer micelles exhibit two levels of hierarchical self-assembly: the process of micellization itself, and the ordering of these micelles onto a lattice. By a combination of small angle x-ray scattering and neutron scattering, we show that both levels of self-assembly are affected when non-adsorbing homopolymer is added to the solutions. The phenomena are analogous to depletion interactions in colloid/polymer mixtures. We have chosen poly(styrene-$b$-isoprene) micelles dissolved in diethyl phthalate as the model system. To these solutions polystyrene homopolymer was added. The effects strongly depend on the molecular weight and concentration of the added homopolymer. We find an induced attraction between micelles at moderate micelle concentrations, and a preference for fcc over bcc lattices in more concentrated solutions. [Preview Abstract] |
Tuesday, March 11, 2008 10:00AM - 10:12AM |
H18.00009: Influence of Electric Fields on the Phase Behavior of Concentrated Block Copolymer Solutions Kristin Schmidt, Heiko Schoberth, Alexander B\"oker We investigate the influence of the electric field on the phase behavior of diblock copolymer concentrated solutions using synchrotron SAXS. We find a significant dependence of the characteristic domain spacing on the electric field strength. For lamellae aligned parallel to the electric field direction we observe that the lamellar spacing decreases with increasing field strength, while for perpendicularly oriented lamellae the domain spacing increases. We also find that the electric field can induce an order-order transition if the block copolymer has a composition close to the predicted phase boundary. Due to the lower free energy of aligned anisotropic microdomain structures parallel to the electric field, we can induce a transition from the metastable hexagonally perforated lamellar phase to the lamellar phase without perforations by applying strong electric fields. Similarly an isotropic cubic gyroid phase, which is stable in the absence of, but cannot be aligned by, the field, transforms to aligned cylinders when a strong electric field is applied. [Preview Abstract] |
Tuesday, March 11, 2008 10:12AM - 10:24AM |
H18.00010: Well Ordered Melts from Low Molar Mass Pluronic Copolymers Blended with Poly (acrylic acid): Effect of Homopolymer Molar Mass Vikram Daga, Vijay Tirumala, Alvin Romang, Eric Lin, James Watkins The use of short chain block copolymer melts as nanostructured templates is often limited by their low segregation strength ($\chi N)$. Since increasing molar mass to strengthen segregation also increases the interdomain spacing, it is more desirable to increase the segment-segment interaction parameter, $\chi $ to produce strong segregation. We have recently shown that block copolymer melts with a molar mass less than 15 kg/mol undergo disorder-to-order transition without a significant increase in interdomain spacing when blended with a selectively associating homopolymer, due to an apparent increase in effective $\chi $. Here, we study the effect of homopolymer molar mass on the segregation of a disordered poly (oxyethylene-oxypropylene-oxyethylene) copolymer melt that forms lamellar microstructure in the ordered phase. Based on small-angle scattering measurements, we find that the melts remain ordered over a broad range of homopolymer chain lengths, ranging up to ten times that of the copolymer. This approach has many implications for the use of commodity block copolymer surfactants as inexpensive nanostructured templates for commercial applications. [Preview Abstract] |
Tuesday, March 11, 2008 10:24AM - 10:36AM |
H18.00011: Novel Characterization of Critical Micelle Concentrations of Block Copolymers and Gradient Copolymers in Homopolymer Robert Sandoval, Daniel Williams, Christopher Wong, Jungki Kim, John Torkelson Here we demonstrate a new method based on the intrinsic fluorescence of styrene-containing block copolymers and gradient copolymers to determine the critical micelle concentrations (cmcs) of copolymers present at low levels in homopolymer. The method relies on the fact that the when styrene/methyl methacrylate (S/MMA) block copolymers and gradient copolymers are well dispersed in a glassy homopolymer such as poly(methyl methacrylate) (PMMA), only monomer fluorescence and no excimer fluorescence is observed from the copolymer. When micelle formation occurs, then excimer fluorescence is present. With this simple method, we have found that gradient copolymers yield much lower cmc values (about an order of magnitude smaller) than comparable block copolymers of similar molecular weight and overall composition. We are extending these studies to consider the effects of block copolymer molecular weight and composition as well as homopolymer molecular weight on the cmc values. While these parameters have received heavy consideration from a theoretical standpoint, little experimental work has focused on these issues. [Preview Abstract] |
Tuesday, March 11, 2008 10:36AM - 10:48AM |
H18.00012: The influence of macromolecular architecture on the micellization in block copolymer/homopolymer blends E. Pavlopoulou, K. Chrissopoulou, S.H. Anastasiadis, G. Portale, W. Bras, H. Iatrou, S. Pispas, N. Hadjichristidis We investigate the micellar formation and micelle characteristics of block copolymers of varying architecture within homopolymer matrices. A series of symmetric (polyisoprene)$_{n}$(polystyrene)$_{n}$ (I$_{n}$S$_{n}$) miktoarm star block copolymers, with n identical pairs of arms, and a series of (polyisoprene)$_{2}$(polystyrene), I$_{2}$S, graft copolymers with constant total MW and varying composition, $f_{PS}$, are added to a low MW PI homopolymer matrix and the blends are investigated by small-angle X-ray and light scattering as a function of copolymer concentration and n or $f_{PS}$. The functionality of the junction point of the copolymer does not influence the characteristics of the I$_{n}$S$_{n}$ micelles, while $f_{PS}$ controls the behavior of the I$_{2}$S grafts. A simple thermodynamic model is developed that describes theoretically the micellization of A$_{n}$B$_{n}$ copolymers within B homopolymers and its predictions agree very well with the experimental data both qualitatively and quantitatively. Sponsored by NATO's Scientific Affairs Division, by the Greek GSRT and by the EU. [Preview Abstract] |
Tuesday, March 11, 2008 10:48AM - 11:00AM |
H18.00013: Phase Behavior and Dimensional Scaling of Symmetric Block Copolymer-Homopolymers Ternary Blends in Thin Films Guoliang Liu, Mark Stoykovich, Shengxiang Ji, Paul Nealey We have studied the phase behavior and dimensional scaling of symmetric ternary blends of PS-$b$-PMMA block copolymers and the respective PS and PMMA homopolymers in thin films. Below the order disorder transition (ODT) temperature, the symmetric ternary blends form lamellae, microemulsion and macrophase separated phases as a function of $\chi $N, $\alpha $ (ratio of degree of polymerization of homopolymers to that of the block copolymer), and \textit{$\phi $}$_{{\rm H}}$ (volume fraction of homopolymers). The phase transition compositions from lamellae to microemulsion and from microemulsion to macrophase separation depend weakly on $\chi $N and $\alpha $ in the range of 12.7$\le \chi $N$\le $37.6 and 0.20$\le \alpha \le $0.99. The dimensions of swollen lamellae and microemulsion ($L_{B})$ can be determined as a function of \textit{$\phi $}$_{{\rm H} }$ and $\alpha $, explicitly, $L_{B}=L_{o}$/(1-\textit{$\phi $}$_{{\rm H}})^{\beta }$, where $L_{o }$is the natural bulk period of pure block copolymer, and\textit{ $\beta $} is a parameter depending strongly on $\alpha $. [Preview Abstract] |
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