Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session S30: Polymer Blends |
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Sponsoring Units: DPOLY Chair: Alamgir Karim, NIST Room: LACC 505 |
Wednesday, March 23, 2005 2:30PM - 2:42PM |
S30.00001: Thermodynamics and Dynamics of Diblock Copolymers at Polymer/Polymer Interfaces Benedict J. Reynolds, Megan L. Ruegg, Nitash P. Balsara, C. J. Radke The efficacy of diblock copolymers for stabilizing interfaces between immiscible polymers depends on both thermodynamic and dynamic factors. We have exploited the slow dynamics of polymer chains to prepare two surfactant-bearing polymeric interfaces that are initially out of equilibrium. The distance between the interfaces was varied from 50 to 600 nm, and the transport of the surfactant molecules from one interface to another was measured by dynamic secondary-ion mass spectroscopy. This transport depends on the traditional diffusion coefficients and the depth of the thermodynamic potential wells that trap the surfactant molecules at the interfaces. The diffusion coefficients of our system were measured in independent experiments and the well depths were obtained from SCFT using a Flory-Huggins interaction parameter and statistical segment lengths measured by small-angle neutron scattering from homogeneous binary blends. This enables a comparison of our experimental interfacial transport measurement and theoretical predictions with no adjustable parameters. [Preview Abstract] |
Wednesday, March 23, 2005 2:42PM - 2:54PM |
S30.00002: Thermodynamics of Polymer Blends Organized by Balanced Block Copolymer Surfactants Studied by Mean-field Theories and Scattering Megan Ruegg, Benedict Reynolds, Nitash Balsara, Timothy Shaffer, Min Lin, David Lohse The phase behavior of multicomponent blends of two immiscible homopolymers (A,B) and an A-C diblock copolymer was studied by scattering experiments and mean field theories. The interactions between the components were tuned to create organized blends with the copolymer serving as a surfactant. The morphology of A/B/A-C blends changed between lamellar phases, microemulsions, homogeneous phases and macrophase- separated states simply by adjusting the temperature. The experimentally determined phase transition temperatures and domain spacings were compared with calculations based on the Random Phase Approximation (RPA) and Self-Consistent Field Theory (SCFT). The only inputs into the calculations were the binary Flory-Huggins interaction parameters (chi) between the three kinds of monomers in our system, and statistical segment lengths. The domain spacing determined from theory was often within 5\% of the experimental values. In a particular range of molecular weights, we find that a critical A/B blend can be organized into a periodic phase by the addition of only 5\% of the diblock copolymer. To our knowledge, all previous experiments that have led to organized critical mixtures have required a significantly larger copolymer concentration. [Preview Abstract] |
Wednesday, March 23, 2005 2:54PM - 3:06PM |
S30.00003: Effects of Branch Points and Chain Ends on Interfacial Segregation and Bulk Thermodynamics in Blends of Branched and Linear Polymers Jae S. Lee, Nam-heui Lee, Alexei P. Sokolov, Roderic P. Quirk, Mark D. Foster, Boualem Hammouda, Charles F. Majkrzak The effects of the number of branch points and number of chain ends in a branched chain on interfacial segregation and bulk thermodynamics in binary blends of well-defined, regularly branched polystyrenes with their linear analogues were studied. A novel series of molecules in which the numbers of branch points and numbers of chain ends in the branched molecule were varied in a controlled way was key to the study. The value of the effective interaction parameter determined from small angle neutron scattering data increased both with increasing the number of branch points and the number of chain ends. Neutron reflectometry and Surface Enhanced Raman Spectrometry measurements showed the preferential segregation of the branched molecules to both interfaces of blend films. The strength of the segregation generally increased by increasing the number of branch points while the number of end groups was kept constant at six. The degree of segregation also increased by increasing the number of end groups while keeping the number of branch points constant at four. [Preview Abstract] |
Wednesday, March 23, 2005 3:06PM - 3:18PM |
S30.00004: Ultra-low interfacial tensions of a polymer/polymer interface with diblock copolymer surfactant Kwanho Chang, David Morse, Christopher Macosko The equilibrium interfacial tension between immiscible homopolymers A and B mixed with an AB copolymer reaches a minimum value $\gamma_{sat}$ beyond a critical concentration of copolymer at which the copolymer begins to self-assemble into micelles or a bicontinuous microemulsion. This saturation value has been measured with a spinning drop tensiometer for systems of poly(isoprene) (PI), poly(dimethyl siloxane) (PDMS), and PI-b-PDMS copolymers, for a sequence of 11 copolymers with PDMS volume fractions $f=0.5 - 0.73$. Ultra-low tensions of $\gamma_{sat} \simeq 10^{-3}$ mN/m have been measured for copolymers with $f = 0.5$. Self-consistent field theory predictions of the tension between a PI phase and a PDMS phase containing swollen micelles agree very well with measured values for copolymers with $f \geq 0.61$. For $f = 0.5 - 0.6$, however, measured values of $\gamma_{sat}(f)$ are much lower than predicted by this theory, and exhibit a discontinuous dependence on $f$ at $f \simeq 0.6$. We suggest that the behavior observed for nearly balanced copolymers could be due to formation a middle-phase bicontinuous microemulsion phase that wets the macroscopic PI-PDMS interface. [Preview Abstract] |
Wednesday, March 23, 2005 3:18PM - 3:30PM |
S30.00005: Kinetic Hindrance during Diffusion-Controlled Reactions at Polymer-Polymer Interfaces Shane Harton, Frederick Stevie, Harald Ade We have characterized diffusion-controlled (DC) reactions between 75kDa hydroxy-terminated deuterated polystyrene (dPS-OH) and several acyl chloride functionalized poly(methyl methacrylates) (PMMA) using dynamic secondary ion mass spectrometry (DSIMS). When annealed at 393-408K, these systems consistently show a depletion hole at early times, which is indicative of DC reactions, but this depletion hole disappears over time with an apparent reaction extinction. This extinction is characterized by an interfacial excess of block-copolymer (Z*) that is considerably lower than current theories predict. This indicates that reactions at highly immiscible polymer-polymer interfaces, whether inherently DC or reaction- controlled, may actually be controlled primarily by kinetic hindrance at the interface rather than long-range diffusion or reaction mechanisms. To probe this directly, we have measured the extinction excess (Z$_{e})$ as a function of reactive dPS-OH concentration in the PS matrix ($\sim $ 5-20 {\%}) and reaction temperature ($\sim $ 403-433K). The variation of the Z$_{e}$ as a function of initial dPS-OH concentration confirms kinetic hindrance as the underlying cause of the reaction extinction, as opposed to loss of reactivity, because the reactive chains are never fully depleted, and the coupling reactions implemented here are extremely robust and completely irreversible. An effective activation energy is determined from the temperature dependency of the Z$_{e}$. [Preview Abstract] |
Wednesday, March 23, 2005 3:30PM - 3:42PM |
S30.00006: Phase Behavior of Ternary Block Copolymer – Homopolymer Blends in Thin Films on Chemically Nanopatterned Surfaces Mark P. Stoykovich, Harun H. Solak, Paul F. Nealey Ternary blends of lamellar-forming block copolymers and homopolymers exhibit a complex phase behavior in the bulk with ordered lamellar, two-phase, and disordered morphologies coexisting at a Lifshitz multicritical point. The onset of the unbinding transition and the associated bicontinuous microemulsion phase is predicted to be a function of $\alpha $, the ratio of the degree of polymerization of the hompolymer to the block copolymer. Here we investigate the phase behavior of ternary blends with varying $\alpha $ and lamellar periods, Lb, in thin films on chemically striped surfaces with period Ls. Our findings indicate that: 1) in contrast to model predictions for bulk systems, the unbinding transition is not strongly dependent on $\alpha $, 2) a blend in the microemulsion phase forms lamellar structures on patterned surfaces, 3) chemical surface patterns can induce phase separation of the ternary blend, and 4) the homopolymer components can distribute themselves in such a way as to form adjacent lamellar domains with different Lb. The technological importance of these findings is the ability of ternary blend systems to epitaxially self-assemble into imaging materials for sub-30 nm lithography. [Preview Abstract] |
Wednesday, March 23, 2005 3:42PM - 3:54PM |
S30.00007: Nucleation in Polymer Blends Timothy Rappl, Nitash Balsara The initial stages of phase separation in an off-critical binary mixture of model polyolefins were studied by time-resolved small angle neutron scattering. We focus on nucleation in the metastable regime which is bounded by the binodal, the location where the nucleation barrier is infinite, and the spinodal, where the nucleation barrier is unimportant. This broad range of barrier heights renders study of the early stage of nucleation a challenging endeavor. We have met this challenge by subjecting our blend to both single- and two-step quenches within the phase separated region of the phase diagram. This enables measurement of the size of the critical nucleus over 80{\%} of the metastable regime. Some aspects of nucleation kinetics follow the linearized theory of Cahn, Hilliard, and Cook, which was originally developed to describe spinodal decomposition. [Preview Abstract] |
Wednesday, March 23, 2005 3:54PM - 4:06PM |
S30.00008: Discrete combinatorial phase mapping of multicomponent mixtures Joao Cabral, Alamgir Karim We report an experimental investigation of the bulk phase behavior of multicomponent mixtures using a novel discrete combinatorial approach. The technique involves a parallel cloud point detection scheme using discrete composition libraries, which are scanned across a temperature range and optically imaged. Sample substrates are microwell arrays fabricated by contact photolithography on a glass coverslip. Polymer blend libraries are generated using a custom built, programmable liquid dispenser system. The sample arrays are placed in a uniform, but continuously varying, temperature field, scanning the mixture across its phase boundary. Optical turbidity is detected by imaging the entire array and the cloud point curve is determined through automated parallel image analysis. In this demonstration, we investigate mixtures of low molecular mass poly(styrene) and poly(butadiene), exhibiting upper critical solution temperature (UCST) phase behavior. The cloud point curves obtained closely approximate the bulk binodal line, and have a high composition resolution of delta phi = 0.01 (volume fraction), using 10 x 10 sample arrays. We discuss thermodynamic and kinetic effects induced by the addition of copolymers and nanoparticles. [Preview Abstract] |
Wednesday, March 23, 2005 4:06PM - 4:18PM |
S30.00009: Small Angle Neutron Scattering Studies on Blends of Poly (Styrene-ran-Vinyl Phenol) with Liquid Crystalline Polyurethane Rujul Mehta, Mark Dadmun Molecular composites, composed of uniformly dispersed rigid-rod liquid crystalline polymer (LCP) molecules in a flexible amorphous polymer matrix, have remained hitherto elusive due to a scarcity of miscible systems containing a LCP and an amorphous polymer. The production of such a blend, with an experimentally accessible miscibility window, has become possible by modifying the architecture of the flexible polymer, so as to induce favorable intermolecular hydrogen bonding. Specifically, liquid crystalline polyurethanes (LCPU) are found to be miscible with a copolymer of styrene and vinyl phenol; with optimum hydrogen bonding between the carbonyl groups of the urethane linkages and the hydroxyl groups present in the styrenic matrix. Availability of a truly miscible molecular composite presents a unique opportunity of studying the confirmation of polymer chains containing rigid-rods that are uniformly dispersed in a flexible coil matrix. A system consisting of the LCPU and the deuterated styrenic copolymer containing 20{\%} vinyl phenol is examined by Small Angle Neutron Scattering at the National Center for Neutron Research at Gaithersburg and Technology, and the Institute of Solid State Research (IFF) at J\"{u}lich. Scattering curves for neat dPS-VPh did not fit the Debye-Bueche model; indicating complex structure. A two correlation length Debye-Bueche model was considered to accommodate for this nonlinear behavior. This model utilizes four fitting parameters, including two correlation lengths a$_ {1}$ and a$_{2}$, corresponding to a Debye-Bueche model and Guinier model. [Preview Abstract] |
Wednesday, March 23, 2005 4:18PM - 4:30PM |
S30.00010: Binary Phase Diagrams of Crystalline Polymers Thein Kyu, Rushikesh Matkar We have extended the phase field free energy for polymer crystallization to binary crystalline polymer blends to generate phase diagrams that are capable of describing a rich variety of phases including eutectic, peritectic, and a host of other intermediate cases. The thermodynamics of liquid-liquid mixing have been modeled based on the Flory-Huggins theory with a $\chi $ interaction parameter. Various coexistence regions have been computed self-consistently by extending the phase field theory of crystallization to binary systems in conjunction with the coupling terms between phase separation and crystallization. The calculated phase diagrams exhibit rich variety of coexistence regions such as liquid + liquid, liquid + crystal, crystal + crystal and neat crystal regions. To describe the spatio-temporal evolution of crystalline morphology, a conserved concentration order parameter and a non-conserved crystal phase order parameter have been utilized in the context of the time-dependent Ginzburg-Landau (TDGL) model C, viz. model A for crystallization and TDGL model B for phase separation. The emerging crystalline morphology is discussed. [Preview Abstract] |
Wednesday, March 23, 2005 4:30PM - 4:42PM |
S30.00011: Spectroscopic Investigation on Morphology Development of Polymer Blends Tomoko Hashida, Young Gyu Jeong, Ying Hua, Shaw Ling Hsu For the first time, high spatial resolution ($\sim $1 $\mu $m$^{2})$ Raman micro-spectroscopy has been used to measure the composition and crystallite distribution of various crystallizable polymer blends. Crystallization kinetics and the degree of crystallinity were characterized using a combination of optical microscopy, thermal analysis, and time resolved FT-IR spectroscopy. These investigations were conducted for a number of binary blends incorporating crystallizable poly(hexamethylene adipate) (PHMA) or poly(hexamethylene sebacate) (PHMS) mixed with non-crystallizable poly(propylene glycol) (PPG). Although the two polyesters have similar chemical structure, they exhibit different phase behavior. Ternary blends including a high glass transition temperature ($T_{g})$ component were also studied. The local composition of polyester was found to control crystallization kinetics and degree of crystallinity. The compositional distribution in the polyester-rich phase was inhomogeneous. Surprisingly, the degree of crystallinity measured for polyesters did not necessarily correspond to the composition profile. The role of the third relative immobile component significantly changed both chemical and morphological distributions. [Preview Abstract] |
Wednesday, March 23, 2005 4:42PM - 4:54PM |
S30.00012: Glassy states and microphase separation in crosslinked homopolymer blends Paul Goldbart, Christian Wald, Annette Zippelius We address the physical properties of blends of distinct homopolymers, crosslinked beyond the gelation point, via a Landau approach involving a pair of coupled order-parameter fields: one describing vulcanization, the other describing local phase separation [1]. Thermal concentration fluctuations, present at the time of crosslinking, are \lq\lq frozen in\rq\rq\ to the gel network. The resulting glassy fluctuations are analyzed at the Gaussian level in various regimes, determined by the relative values of certain physical length-scales. We also analyze the enhancement, due to crosslinking, of the stability of the blend with respect to demixing. Beyond the corresponding stability limit, complete phase separation is prevented by gelation and replaced by microphase separation, which occurs up to a length-scale set by the mesh size of the network, as a simple variational scheme reveals. [1] C. Wald, A. Zippelius and P. M. Goldbart, cond-mat/0411056. [Preview Abstract] |
Wednesday, March 23, 2005 4:54PM - 5:06PM |
S30.00013: Coarse-Grained Description of Polymer Liquids and their Mixtures as Interacting Soft-Colloidal Particles Marina Guenza, Galina Yatsenko, Edward Sambriski, Maria Nemirovskaya We present a novel theoretical approach which maps polymer melts and their mixtures onto fluids of soft-colloidal particles. From liquid-state theory we derive analytical center-of-mass total pair correlation functions, which reproduce those computed from united-atom simulations with no fitting parameters. The coarse-grained description correctly bridges micro- and mesoscopic fluid properties. Molecular dynamics simulations of soft colloidal particles interacting through the calculated effective pair potentials are consistent with data from microscopic-scale simulations and analytical formulas. [Preview Abstract] |
Wednesday, March 23, 2005 5:06PM - 5:18PM |
S30.00014: Polyolefin blends: Coarse-grained study of melt structures relevant for predicting blend miscibilities Sandeep Jain, Shekhar Garde, Sanat Kumar Miscibility of polyolefins has been the subject of intense research both due to its fundamental importance and industrial applications. Detailed Molecular Dynamics (MD) simulations of long chain polymers and their phase behavior is limited by the enormous computational effort involved. Naturally, emphasis is being placed on development of coarse-graining strategies that allow more efficient sampling of conformational space while retaining the chemical identity of the polymer of interest. We will present results from a novel coarse-graining approach that combines detailed MD simulations of oligomers with inverse (Monte Carlo based) methods to obtain interaction potentials in coarse-grained system. We show that the coarse-grained potentials, thus generated, reproduce a variety of structural properties of the underlying polymer melt systems. The computational efficiency of our coarse-graining apporach allows simulations of truly polymeric (long chain) melts. Extension of these ideas to studies of polyolefin blends with emphasis on miscibility will be presented briefly. [Preview Abstract] |
Wednesday, March 23, 2005 5:18PM - 5:30PM |
S30.00015: Miscible polyethylene glycol-citric acid gels Justin Barone Polyethylene glycol (PEG) and citric acid (CA) are crystalline solids at room temperature. They are opaque, hard, brittle materials. However, blending the PEG and CA shows that a clear, soft “gel” is formed at certain concentrations. Rheology, differential scanning calorimetry (DSC), FT-IR, and Raman spectroscopy are used to characterize the behavior of the blends as a function of concentration. The solubility parameters for PEG and CA are the same indicating that complete miscibility is possible. It is found that the PEG and citric acid strongly associate through hydrogen bonding and prevent re-crystallization of either phase. [Preview Abstract] |
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S30.00016: Quantitative Predictions of the Enthalpic Component of the Interaction Parameter in Mixtures: An Assessment of the Accuracy and Precision Required From Molecular Simulations David Rigby The use of force field based atomistic simulation methods to calculate the enthalpic part of the interaction parameter in mixtures containing small molecules or polymers is both conceptually simple and appealing in view of the enormous potential savings in the cost of synthesis and experimental measurements (e.g. when one is seeking a new or modified polymer mixture system). In order for such simulations to be ultimately successful however, it is necessary that they be capable of routinely making accurate predictions of excess thermodynamic properties. This in turn requires both that a force field be capable of high accuracy and that the associated simulation protocol be capable of high precision. This presentation will examine the factors that affect precision and accuracy in typical simulations of experimentally well-studied small molecule mixture systems containing aliphatic and aromatic hydrocarbons, and will further discuss additional sources of uncertainty when the simulations are extended to mixtures of oligomers or polymers comprised of similar aliphatic and aromatic moieties. [Preview Abstract] |
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S30.00017: Three-Dimensional Modeling of Holographic Polymer-Dispersed Liquid Crystal Formation via Various Interference Techniques Thein Kyu, Gregory Yandek, Scott Meng Holographic polymer-dispersed crystalline materials (H-PDLC), useful in many optical applications, maintain periodic alignment of liquid crystalline (LC) domains in polymeric hosts. H-PDLC fabrication entails the exposure of a mixture containing monomer, photo-initiator, and inert LC to geometrically arranged light beams where constructive and destructive interference occurs within the sample. Polymerization dominates in regions of high beam intensity such that LC migrates to areas of low intensity resulting in desired periodic structures. It is advantageous to acquire information regarding the physics of the fabrication process through modeling techniques. By coupling reaction-diffusion equations with the Flory-Huggins theory of mixing, Maier-Saupe relations for nematic ordering, and network elasticity terms, modeling has elucidated information without accruing the costs of trial and error. Results predict that a 35{\%} LC volume content and flexible polymer host materials afford optimal structures. Two- and three-dimensional variations in structures have been predicted. [Preview Abstract] |
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