Session K32 - Poster Session 2.
POSTER session, Wednesday afternoon, March 19
Exhibit Hall D, Conv. Center

[K32.01] A Comparison of Gyroid-Forming Diblock (A_xB_y) and Triblock (A_xB_2yA_x) Copolymers: Thermodynamic and Dynamic Mechanical Properties

A low-molecular-weight poly[ethylene oxide-b\/-(ethylethylene-co\/-ethylene)] (PEO-PEE) diblock copolymer and the corresponding poly[ethylene oxide-b\/-(ethylethylene-co\/-ethylene)-b\/-ethylene oxide] (PEO-PEE-PEO) triblock copolymer were prepared. The compositions in these materials were matched (f_PEO=0.44), and the molecular weight of the triblock is twice of that of the diblock homologue. The difference between the order-disorder transition temperatures in the diblock and triblock is in reasonable agreement with mean-field predictions. Small-angle X-ray scattering experiments support that both of the materials form the gyroid phase in amorphous ordered states. In the gyroid phase, the diblock and triblock materials showed qualitatively similar linear dynamic mechanical behaviors, but a slight difference in the power law scaling of frequency versus modulus was apparent.

[K32.02] Landau-Brazovskii Theory for the \bfIaøverline3d phase

The stability of the so-called "Gyroid" phase, of Iaøverline3d symmetry, observed for lyotropic liquid crystals and block copolymers is accounted for using the Landau-Brazovskii theory of weak crystallization. In the mean field approximation, the Iaøverline3d phase is found to be stable between the lamellar and hexagonal phases close to the disordered liquid phase. When allowance is made for Brazovskii critical fluctuations, a direct phase transition between the disordered liquid and Iaøverline3d phases is shown to be possible, in agreement with experimental observations.(V.E.Podneks and I.W.Hamley, \itJETP Letters, in press).

[K32.03] Internal Chain Dynamics in High MW Diblock Copolymers: Thermodynamic Effects

The dynamic structure factor S(q,t) is probed in disordered semidilute solutions of very high MW diblock copolymers for wavevectors q near the maximum of the static S(q). Two modes of relaxation of composition fluctuations are observed: the internal copolymer mode with the effect of the proximity to the ODT evident both in the static light scattering intensity and in the relaxational dynamics by increasing the copolymer concentration towards the ODT; and an extra faster relaxation, less influenced by the thermodynamics. A complete theory for entangled systems is presented which quantitatively describes the internal relaxation within the reptation model and predicts the existence of another relaxation mechanism due to Rouse-like motions related to curvilinear chain fluctuations inside their tubes; theory quantitatively accounts for the combined characteristics of the two processes.

[K32.04] Chain Folding in Crystallisable Block Copolymers.

The crystallisation of oxyethylene/oxybutylene (E/B) diblock copolymers has been studied by optical microscopy, atomic force microscopy and simultaneous SAXS and WAXS. The copolymers crystallised from their melts (disordered, lamellar or hexagonal) with folded E blocks. Spherulite growth rates were studied by optical microscopy and minima in crystallisation rate are associated with chain folding transitions. Atomic force microscopy allowed the crystal thickness to be observed directly from steps and terraces in thin films. Rapid crystallisation (quench) of the longer copolymers led to structures with multiply-folded E blocks and the B blocks essentially unstretched. These metastable folded structures formed during rapid crystallisation did not unfold on heating, but could be self-seeded to grow equilibrium once-folded (or multi-folded) structures. The folded states are discussed in terms of contributions to the Gibbs energy of crystallisation from E-block folding and B-block stretching and the cross-sectional area associated with each block.

[K32.05] Interfacial Curvature and Morphology in Block and Graft Copolymers

The interfacial mean curvature (H) has been characterized for polyisoprene-polystyrene I2S simple graft block copolymers and for polyisoprene-poly(t-butylmethacrylate) (PtBMA) linear, conformationally asymmetric diblock copolymers using TEM and SAXS. It is found that conformational and architectural asymmetry of the I2S and PI-PtBMA blocks produce two effects: A shift in the observed interfacial mean curvature away from the typical PI-PS diblock behavior, and (2) A marked difference in the ability of cylindrical domains to form microstructures with long range order depending on which component is in the microdomain core and which is in the corona. A simple model was formulated that allows the prediction of the preferred H and Gaussian curvature (K), based on the molecular parameters, by minimizing free energy with respect to interfacial curvature. This model yields two families of minima, one corresponding to a family of spherical structures and one corresponding to a family of cylindrical structures. The cylinder family was found to merge continuously into bicontinuous structures, identified by the development of a preference for negative interfacial K.

[K32.06] Complex Phase Behavior in Triblock Copolymer/Homopolymer Blends

The existence of complex bicontinous phases such as the gyroid in diblock block copolymer systems has been the focus of many recent studies. While obtaining these structures in neat diblock block copolymers is nontrivial due to the small region in phase space that they occupy, greater access to these facinating morphologies can be enjoyed through physical sythesis; i.e., by blending block copolymers with fully miscible block-specific homopolymers. Previous studies, however, have focused on blends with copolymers having monoconformational blocks. In this study, we extend this methodology to a lamellar poly(styrene-b-isoprene-b-styrene) (SIS) triblock copolymer which has a biconformational midblock. Blends of this copolymer with homopolyisoprenes (hI) of varying molecular weights are found to exhibit "non-classical" morphologies. To identify these morphologies and develop conformation-morphology-property relationships, we employ a combination of energy-filtered transmission electron microscopy, small-angle x-ray scattering and dynamic mechanical analysis.

[K32.07] Nearly Monodisperse, Uniformly Tapered Copolymers Made via "Living" Free Radical Methods

"Random" copolymers made by "living" free radical methods have been reported to have the same sequence distribution as those made by conventional free radical methods. However, in general, copolymers with different structure are made by the "living" approach. This is due to composition drift in the comonomer mix during reaction (reactivity ratios typically differ from 1.0) and to the fact that in "living" copolymerization each chain has a composition reflecting the drift in comonomer composition up to the finish (high conversion) of the reaction. Computational and experimental examples of tapered-composition copolymers (including cases in which one chain end is a statistical mix with mostly monomer 1 while the other is a block of monomer 2) are given, with styrene as a monomer. When reactivity ratios for the monomers are nearly 1.0 (e.g. styrene and p-methyl styrene), similar copolymers are made by the two methods. Block copolymer synthesis via living free radical approaches is also discussed. Physical properties of styrene-based copolymers made by living radical methods are presented.

[K32.08] Architecturally and Compositionally Induced Long-range Order of Microphase Separated Block Copolymer Microstructure

The morphological behavior of three series of miktoarm star block copolymers was characterized via transmission electron microscopy (TEM) and small-angle x-ray and neutron scattering (SAXS, SANS). The novel molecular architectures of the star molecules, in combination with unique relative volume fractions of the respective polyisoprene and polystyrene block species, provide for spherical, cylindrical, and lamellar morphologies with extremely well developed long range order. The samples were only quiescently cast from dilute solutions but displayed lattices with perfection usually only found in shear aligned block copolymer systems. General rules for predicting lattice perfection can be deduced from the experimental data and are corroborated with free energy potential calculations based on brush free energy formalisms.

[K32.09] Morphologies of A_2B Simple Graft Copolymer Blends: Copolymer/Copolymer and Copolymer/Homopolymer Systems to Further Elucidate the Stability of Simple Graft Phase Behavior

The morphological behavior of two series of binary blends of A_2B simple graft block copolymers (A is polyisoprene and B is polystyrene) was characterized via transmission electron microscopy (TEM) and small-angle neutron scattering (SANS). Binary blends of A_2B samples with other A_2B samples of similar relative volume fractions were composed to map out the volume fraction window of stability of the randomly oriented worm phase, or ROW. This novel equilibrium phase behavior was found to occur in a neat A_2B sample with a B volume fraction of 0.81. At this unique composition the single B graft chain first becomes large enough to force the two A chains to the concave side of the AB interface in the microphase separated state. Another set of binary blends of A_2B samples was composed with the respective homopolymers in order to more rigorously determine the phase boundaries relative to volume fraction of the respective microphase separated morphologies in the A_2B systems.

[K32.10] Inverted Order-Disorder Transition in Diblock Copolymers: Pressure Dependence and Microscopy Studies

Diblock copolymers of perdeuterated styrene and n-butyl methacrylate have been shown to undergo a lower order-disorder transition (LODT) - miscibility at intermediate temperatures gives way to ordered mesophase domains at high temperatures. Several aspects of this transition will be discussed. First, since the transition is driven by unfavorable entropy of mixing contributions, the LODT has strong pressure dependence; results from pressure-dependent small-angle neutron scattering will show a shift in the LODT to higher temperatures with increasing pressure. Second, electron microscopy studies on the morphology of the copolymer above the LODT will be shown. Finally, a comparison between experimental results and a mean-field theory will be presented.

[K32.11] Micro- and Macro-phase Transition Processes in Immiscible Blends of Poly(styrene-b-ethylene propylene) with Poly(styrene-b-isoprene)

The phase separation and ordering processes in solution cast films of immiscible binary blends of Poly(styrene-b-ethylene propylene) (SEP) with Poly(styrene-b-isoprene) (SI) were studied as a function of SI concentration and molecular weight by transmission electron microscopy (TEM). At all blend compositions, macrophase separation between SEP and SI occurs via a nucleation and growth process, followed by microphase separation, first within the SEP-rich, and later within the SI-rich macrodomains. These processes significantly affect the shape of dispersed phase. At low SI concentration, SI-rich phases, showing scalloped shapes, are dispersed in the SEP matrix. Increasing SI content over 60 wtellipsoidal SEP-rich phases, containing small SI blobs and lamellae, are dispersed in SI matrix. These SI inclusions diffuse into the center of SEP dispersed phase, when the molecular weight of SI was decreased. The effect of solvent evaporation rate on morphology is also discussed. Rapid evaporation yields similar, yet finer scale, morphologies, indicating that the macrophase separation is governed by a nucleation and growth process.

[K32.12] Structure and Properties of Complex Phases in PE-PEE Block Copolymers

We reexamined the complex phase behavior of several poly(ethylene)-poly(ethylethylene) diblock copolymers with poly(ethylene) block volume fractions (f_PE) ranging from 0.60 to 0.70 by means of binary blends of f_PE = 0.60 and 0.75 pure diblock copolymers near the order-disorder transition (ODT). Dynamic Mechanical Spectroscopy, TEM and X-ray scattering experiments were used to investigate characteristics of these polymers. We found the gyroid phase in this regime, which was previously identified as the hexagonally modulated layer (HML) and hexagonally perforated layer (HPL) phases. The HML and HPL phases have been identified as transient non-equilibrium phases as anticipated by the recent mean-field theory of Qi and Wang(S. Qi and Z.-G. Wang, Phys. Rev. E, in press.). We conclude that the complex phase transition behavior depends on kinetics rather than thermodynamics.

[K32.13] Light Scattering from Poly (styrene-b- methylmethacrylate) Block Copolymer Solutions

Elastic light scattering experiments have been performed on a poly(styrene-b-methylmethacrylate)(PS-PMMA, Mw = 1,170,000 g/mole, \phi_PS =0.75) diblock copolymer in two different solvents : i) ethylbenzoate, isorefractive with PMMA and ii) (bromobenzene/1-chloronaphthalene) mixed solvent, having a refractive index intermediate between those of PS and PMMA and satisfying the zero average contrast condition at the temperature T=15^\circC. The experiments were carried out at different scattering angles \theta from 30^\circ to 130^\circ and at different concentrations covering the dilute and the semi-dilute regimes, namely (0.3<(c/c*)<5). The results show a good agreement with the theoretical predictions based on the random phase approximation (RPA). At higher concentrations, however, a clear deviation is observed.

[K32.14] Tensile and Fatigue Behavior of Poly(ether-ester) Block Copolymers.

Compression molded poly(ether-ester) block copolymers based on hard segments of poly(tetramethylene terephthalate) (PTMT) and/or poly(tetramethylene isophthalate) (PTMI) and soft segments of poly(tetramethylene oxide) have been prepared and subjected to constant-strain tensile testing and fatigue testing. The fatigue test utilized a stress-controlled haversine cyclic load. Results indicate the influence of hard segment type (PTMT vs. PTMI) and crystallinity (weight percentage of hard segment) on the tensile and fatigue strength of these block copolymers. Stress-strain, stress to failure cycle (S-N Curve), dynamic viscoelastic properties during the fatigue process, and Scanning Electron Microscopy (SEM) views of fractured surfaces will be presented.

[K32.15] Morphological Characterization=7F of 16-Miktoarm Vergina Star Block Copolymers

The morphological behavior of a series of well-defined miktoarm star block copolymers having 16 arms per molecule was characterized using transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and small-angle neutron (SANS) techniques. The molecules, called "Vergina" stars, have 8 arms of polyisoprene and 8 arms of polystyrene radiating from a single junction point. The samples were found to microphase separate into lamella of varying thickness. This behavior was the same as that of diblock copolymers of equivalent volume fractions, a result predicted from theoretical considerations. Incorporating results from previous studies in the literature of miktoarm block copolymers containing trifunctional and tetrafunctional branch points as well as the new Vergina star data, the scaling behaviors of the area per junction and domain dimensions versus junction functionality were investigated.

[K32.16] Linear and Nonlinear Viscoelastic Behavior of Polymer Blends near Phase Separation

The shear rheology of binary polymer blends is investigated in the vicinity of phase separation. In the linear viscoelastic regime, the material functions are sensitive to phase separation and the effects of critical concentration fluctuations, which dominate the mechanical response, are quantified yielding both the binodal and the spinodal curves. The glass transition asymmetry of the blend investigated is important in determining the magnitude of the effects that correlate with the phase behavior, and, thus, it may affect to some degree the accuracy of the rheologically estimated phase diagram. The steady shear non-linear properties are weakly sensitive to phase separation and suggest that shear induced mixing might be possible. Further, they indicate the importance of strain energy to the interplay between steady shear flow and phase separation. On the other hand, the linear viscoelastic properties of the phase-separated blends are adequately described by a simple incompressible emulsion model considering a suspension of droplets of one coexisting phase in the matrix of the other phase.

[K32.17] Dielectric Investigation on the Dynamics of Phase Separated Binary Polymer Blends

The segmental relaxation of a series of Poly(styrene)/Poly(methylphenylsiloxane) (PS/PMPS) blends was measured by broadband dielectric spectroscopy (10^-2Hz-10^7Hz) in the phase separated regime. Dynamics of the different environments were probed and discussed in terms of the difference between the glass transition temperature T_g of the two components and the phase separation temperature of the mixture. The characteristic width and the relaxation rate of the spectra is associated with the two-phase morphology of the mixture, as well as with the local composition of the phases. The results are compared with recent studies in polymer blend dynamics.

[K32.18] Acetone Transport in Poly(ethylene terephthalate)

This abstract was not submitted electronically.

[K32.19] Morphology of Two-Phase Channel Flow in Extruded Polymer Blends

In situ optical microscopy and static/quasi-static light scattering have been used to study droplet deformation and breakup in channel flow of extruded polyethylene/polystyrene blends. Optical tracking of silica microspheres has been used to measure the velocity field as a function of flow rate in the pure-melt limits, and shear thinning leads to regions of high shear stress near the walls. Droplets of one phase dispersed in a matrix of the other show a rich morphology that depends on position within the channel, flow rate, and the viscosities of droplet and matrix. Measurements on reactive polyethylene/polystyrene blends will be discussed to demonstrate the on-line instrumentation.

[K32.20] Dynamics of Phase Separation in Polymer Blend Melts Under Shear Flow

This abstract was not submitted electronically.

[K32.21] Effect of Sequence Distribution of Linear Copolymers on Their Compatibilizing Ability in Polymer Blends

The role of copolymer sequence distribution on the interfacial characteristics of a ternary polymer blend containing 2 homopolymers and a linear copolymer in the phase separated state are examined using Monte Carlo Simulation. The copolymer does migrate to the biphasic interface in the phase separated regime while the configuration and expansion of the copolymer at the interface is a function of sequence distribution within the copolymer. This effect is interpreted in terms of the efficiency of the copolymer to strengthen the biphasic interface. These results suggest that block, alternating, and block-ran structures show promise as interfacial modifiers, while the purely random and alt-ran copolymers will be less efficient as an interfacial strengthener. It is also found that a variation of the sequence distribution away from a purely random structure can dramatically effect the ability of the copolymer to modify the interface. As most polymers which are not block nor alternating are termed 'random', this differentiation may have an effect on experimental studies of 'random' copolymers as compatibilizers in polymer blends.

[K32.22] Characterization of Thermotropic LCP with Alkyl Side-Group and Polycarbonate Blends

New thermotropic liquid crystalline polymer (LCP) with alkyl side-group was synthesized. Blends of LCP with polycarbonate (PC) were prepared by coprecipitation from a common solvent. The rheological behavior of the LCP/PC blends was found to be very different from that of the PC, and significant viscosity reductions were observed at the temperature ranges of 200-230 ^\circC. The blends were extruded at different LCP contents and different draw ratios from the capillary rheometer. The ultimate tensile strength showed a maximum at the 10 wt% level of LCP in the blends, and then it decreased when the LCP content was higher than 10%. But the initial modulus monotonically increased with LCP content in all cases. The morphology of the blends was found to be affected by their compositions. SEM studies revealed that finely dispersed spherical domains of LCP were formed in the PC matrix. But the SEM micrographs show a poor adhesion between the two phases.

[K32.23] Rheology of the Miscible Polymer Blend Poly(methyl methacrylate) and Poly(styrene-co-acrylonitrile)

The viscoelasticity of a miscible blend of poly(methyl methacrylate) and a random copolymer of styrene and acrylonitrile has been investigated by means of oscillatory shear, and compared to the pure components. The blend components are characterized by closely-matched glass transition temperatures (110 and 130 ^oC for SAN and PMMA respectively). The Flory interaction parameter for this blend \chi = -0.01. The blend contained 20 wt% SAN. We find that the empirical time-temperature superposition principle holds for the pure SAN and the blend between Tg and Tg+55K, and between Tg+20K and Tg+55K for the pure PMMA. Literature neutron scattering data indicate significant concentration fluctuations in this blend system, but the fluctuations do not cause thermorheological complexity because all compositions have nearly identical glass transition temperatures.

[K32.24] Athermal Blend Near a Variety of Surfaces

We consider a model describing athermal blend near a variety of surfaces (attractive, neutral and repulsive). We use recursion technique to solve the model on a finite tree with a surface. The resulting solution yields an approximation for the model on a regular lattice. We report various density profiles, the surface segment density, the surface entropy and free energy as a function of surface interaction.

[K32.25] Phase separation in biopolymer mixtures

A ternary aqueous solution of gelatin and dextran at near critical composition phase separates by an initial process of spinodal decomposition, as revealed by light scattering. The subsequent evolution of the morphology is sensitive to whether the quench temperature is above or below the gelation temperature of the gelatin. Above the gelation temperature, the initially interconnected structure undergoes a transition to a disconnected morphology of droplets; even in the late stage of phase separation IR spectrometry reveals slow changes in the composition of the coexisting phases. Below the gelation temperature, the morphology always remains interconnected, with structures present on an increasingly wide range of length scales. We have also studied the rheology of these mixtures, and find that mixtures of identical compositions can be given thermal histories which result in radically different final values of the storage modulus, according to whether the connectivity of the gelatin rich phase has been maintained.

[K32.26] Random Copolymers as Polymeric Compatibilizers

Some recent results have shown the possibility that random copolymers can be used as polymeric compatibilizers. However, it is not yet clear whether random copolymers can move to the interface during melt processing, and stabilize the resultant morphology during annealing. Polystyrene (PS) and poly(methyl methacrylate) (PMMA) were chosen as model blends, and a random copolymer of styrene and methyl methacrylate (SMMA, 70 wt % styrene) is used as the compatibilizer. We made blend samples using a Haake batch mixer and characterized the blend morphology using TEM. We found that the SMMA moves to the interface between PS and PMMA domains during melt mixing and forms encapsulating layers at the interface. As a result the particle size of the dispersed phase is significantly reduced. However, the size of the encapsulated particles gradually increases during melt annealing, indicating that the encapsulating layer of random copolymer does not provide static stability against coalescence. These experimental results are discussed in terms of an encapsulation model of ternary polymer blends, proposed by Hobbs et al. , and a binary interaction model of random copolymer blends.

[K32.27] Molecular Dynamics Simulation of Pearl Necklace Blends Differing in Site Diameter

Molecular Dynamics simulations of pearl necklace chain blends at liquid packing fractions were performed with varied levels of attractive interactions. Species were distinguished by differing site diameter and Chi parameters were calculated, taking into account differences in site volume and local structure. Other methods of perceiving phase separation were also explored. Comparisons of local structure with Polymer Reference Interaction Site Model (PRISM) projections, were made.

[K32.28] Hydrophilic Surface Preparation on Fluoropolymers via Entropically-Driven Surface Segregation

Earlier studies examined the entropically-driven surface enrichment of the higher energy component in miscible polymer blends via architectural modification of the high-energy additive. Here we extend this work by examining similar blends with a larger cohesive energy difference between components. The segregation of a methacrylate with poly(ethylene oxide) side branches [P(MMA-r\/-MnG)] in a poly(vinylidene fluoride) matrix is studied. The potential utility of this phenomenon in improving the fouling resistance of water filtration membranes is discussed.

[K32.29] Non Mean Field Behavior in Symmetric Polymer Blends

Our recently developed optimized cluster theory of polymer blends was used to investigate the structure and thermodynamic properties of structurally symmetric polymer blends. The theory accounts for the influence compositional and density fluctuations have on these properties. The effective chi parameter, \chi_s, and the critical temperature were determined to be renormalized relative to mean- field theory. Both properties were found to be sensitive to both the functional form and range of the interaction potentials between polymer segments in the mixtures. The observed concave-up compositional dependence of \chi_s decreased with increasing chain length, N, due to the suppression of compositional fluctuations with increasing N. Structural rearrangements in the blends were found to arise from the energetic desire of unlike segments to reduce their contacts. As a result, substantial deviations from random mixing were observed at low to moderate chain lengths. The chain length dependence of the calculated non mean field behavior persisted even in the long chain limit. A comparison will be made with computer simulations and other theories. Extensions to diblock copolymers will also be discussed.

[K32.30] Structure and Thermodynamics of Polyolefin Melts

Subtle differences in the intermolecular packing of various polyolefins can create dissimilar permeability and mixing behavior. We have used a combination of the Polymer Reference Interaction Site Model (PRISM) and Monte Carlo simulation to study the structural and thermodynamic properties of realistic models for polyolefins. Results for polyisobutylene and syndiotactic polypropylene will be presented along with comparisons to wide-angle x-ray scattering experiments and properties determined from previous studies of polyethylene and isotactic polypropylene. Our technique uses a Monte Carlo simulation on an isolated molecule to determine the polymer's intramolecular structure. With this information, PRISM theory can predict the intermolecular packing for any liquid density and/or mixture composition in a computationally efficient manner. This approach will then be used to explore the mixing behavior of these polyolefins.

[K32.31] New Solution for Counterion Condensation Theory

We found a new, exact solution of the nonlinear Poisson-Boltzmann equation in cylindrical geometry describing the counter ion condensation on a strongly charged polymer. In contrast to the Manning condensation theory, the condensation occurs at the critical line charge density \lambda = 3/2, which is 3/2 times larger than in Manning's theory. In Manning theory the condensation occurs in cylindrical cell geometry when electrosasatic energy gain of bringing the counter ion to the surface 2\lambda \log\rho becomes comparable with the 2D entropy loss of the couter ions 2log\rho. Our result describes condensation in a dilute solutions of polyelectrolytes. In this case the couter ion should be brought from the 3D space and the entropy loss is 3/2 times larger than in Manning' case. Therefore the onset of condensation occuers at higher chagre density.

[K32.32] Conductivity of Polyelectrolyte Solutions

We present conductivity data on solutions of the sodium salt of sulfonated polystyrene and solutions of the sodium salt of poly(2-acrylamido-2-methyl propane sulfonate). After extensive dialysis, polyelectrolytes have residual salt present in them. By comparing conductivity data with no added salt to data with controlled additions of NaCl, we can unambiguously determine the contribution of the residual salt to the conductivity of polyelectrolyte solutions of low concentration. This information is utilized to infer the residual salt concentration, assuming the contaminant to be dissolved and dissociated carbon dioxide.

[K32.33] The Structure of Short Chain Models of Li Doped PEO

We believe that molecular simulations of small model molecules and molecular complexes, and comparison of simulation results with experiments, will allow us to develop accurate force fields for simulations of polymeric systems. Demonstration of the accuracy of the representation of the conformational energies and geometries, and coulombic, polarization and van der Waals interactions present in the smaller systems is critical for the validation of a force field to be used in polymer simulations. PEO is a water soluble polymer of considerable technological importance, with the doped form being considered as a solid electrolyte. We report x-ray diffraction measurements on models of undoped and Li^+ doped polyethylene oxide (PEO). The models are short, methyl-terminated sequences of -CH_2-CH_2-O-. The results are compared to MD simulations using accurate representations of molecular flexibility and intermolecular potentials. The small molecule results will also be dicussed vis-a-vis existing experimental and computational work on doped and undoped PEO of macromolecular dimensions. Sponsored by the Div. of Mat. Sci., Office of Basic Energy Sciences, USDOE, under contract DE-AC05-96OR22464 with Oak Ridge Nat. Lab., managed by Lockheed Martin Energy Research Corp.

[K32.34] Effects of solvation on model semiflexible polymers.

We investigate the effects of solvation by simple repulsive solvents on the conformation of semiflexible model pearl-necklace polymers. The dependence of conformational measures such the probability distribution of squared end-to-end distances is calculated for a variety of solvation conditions and backbones stiffnesses, and some unusual effects are observed. For example, it appears possible that a sufficiently stiff polymer may actually become larger when removed from the vacuum and placed in a purely repulsive solvent. Calculations are made both by direct Monte-Carlo computer simulation and simulation of the single chain in a new ``scaled-particle theory'' solvent influence functional.

[K32.35] Molecular Dynamics Simulations of 1,2-dimethoxyethane and Poly(ethyleneoxide) in Aqueous Solution.

We have performed molecular dynamics simulations of 1,2-dimethoxyethane (DME), a model ether for poly(ethyleneoxide) (PEO), in aqueous solution. Simulations were performed as a function of temperature and composition using a quantum chemistry based force field. The simulations yielded PVT behavior of DME solutions in good agreement with experiment. The conformational properties of DME in solution, as well as the structural and dynamic properties of the solutions will be discussed. Initial results of simulations of PEO in aqueous solution using the same for field will also be presented.

[K32.36] Dynamic Poisson-Boltzmann theory of charged polymers

We present a method of performing molecular dynamics simulations of charged polymers that takes into account the instantaneous response of the ionic atmosphere to fluctuations in polymer conformation without employing explicit solvent and counterions. Using density functional theory we write the free energy of the ionic atmosphere around the polymer as a functional of its density in the linearized Poisson-Boltzmann limit. We then define a thermodynamic force on the ion atmosphere density as the negative of the functional derivative of the free energy with respect to variations in the density. By parameterizing the ion atmosphere density we find analytical expressions for both the free energy and the thermodynamic force. We then add to a normal MD simulation of a charged polymer extra degrees of freedom, namely the parameters describing the instantaneous ion atomosphere density. These parameters vary dynamically under the influence of the coupled mechanical and thermodynamic forces, so that the instantaneous variations in the ionic atmosphere as the polymer conformation fluctuates are described. MD simulations were carried out on model soft-core charged polymers and compared to Monte-Carlo simulations of the full polymer + ion atmosphere system.

[K32.37] Constrained Free Energy of Deformed Polymer Systems

This abstract was not submitted electronically.

[K32.38] Micellization and Interactions of Model Ionic Graft Copolymers in Solution

The micellization of model ionic graft copolymers with hydrophobic backbones and ionic grafts has been investigated with small angle neutron scattering. The copolymers can be dispersed in a mixed solvent of 80/20 H2O/THF to form micelles with core-shell morphologies. The structure of micelles was studied a function of grafting density, solvent composition, and ionic strength of the solution. The interactions of the micelles in these solutions were modeled using the Orstein-Zernike equation with the Rogers-Young closure in which the inter-particle potential is of the Yukawa form, suggesting these particles interact in solution very similar to charged colloids.

[K32.39] Critical Examination of the Lattice Cluster Theory

The lattice cluster theory(J. Dudowicz, K.F. Freed and W.G. Madden, Macromolecules 23, 4803 (1990).) is a double expansion around infinite coordination number of the lattice and infinite temperature and is truncated at finite orders. The truncation makes the theory limited in its range of applicability. In order to determine this range, we have calculated the entropy of mixing, the specific heat, the energy of interaction and the spinodal with some puzzling results.

[K32.40] Strength Development At Thermoset Interfaces

A basic set of 10 polymer-polymer matrix interfaces has been identified to play a vital role in the technical apects of composite manufacturing, repair, recycling, welding and joining of thermoset matrix composites. A model vinyl ester resin was used in compact tension experiments with side-A and side-B, to determine the fracture energy G. Surprisingly, G was very small compared to the virgin strength (co-cured side-A with side-B) when liquid resin in side A was cured against previously cured side-B. Apparently, the chain extension reactions were not sufficient to achieve sufficient molecular connectivity at the interface. Several methods of repair were explored for fractured specimens, the most successful being the use of polystyrene connector chains at the interface with a molecular weight near M = 200,000. However, the complete virgin strength was never recovered, despite several chemical treatments, including crack healing. Strength results for all 10 interfaces, subjected to a variety of chemical treatments and surface preparation techniques are presented.

[K32.41] Network formation under applied external fields.

The phase behavior and curing reaction of 1,4-benzenedicarboxylic acid bis(4-cyanatomethylphenyl) ester (LC dicyanate) as well as mechanical properties of the LC network were examined. Similar to conventional dicyanate monomers the overall reaction kinetics were found to be of first order with an activation energy of 67.5 kJ/mol. Gelation occurred at a conversion of ca. 0.5 and was detected by viscoelastic measurements. These results suggest that the polymerization in the LC dicyanate system is the same as for non-LC dicyanates such as 2,2-bis(cyanatophenyl)propane and is not special. Our observations by POM, GPC and DSC indicate that small clusters built of dimers or trimers surrounded by 6-7 monomers dominate the

formation of the mesophase with a clearing temperature higher than 280 0C. The onset of the mesophase buid-up starts at conversions of ca. 0.06 and ends at conversions of ca. 0.20, independent of the curing temperature. Antagonism between the liquid crystalline field and dense crosslinks causes a large free volume in the glassy state and greatly affects the elastic modulus as well as the Tg of the LC network.

[K32.42] Creating an Artificial Muscle

Striated skeletal muscle responds to a nerve impulse in less than 100 ms. In the past, polymeric gels and conducting polymers have been investigated for use as artificial muscle. However, the main problem with these materials is their relatively slow response (>3 seconds). On the other hand, electrorheological (ER) fluids are materials that change from a liquid to a solid upon application of an electric field. These fluids have a response on the order of a millisecond. A novel approach to artificial muscle utilizing the fast time response of ER fluids and the elasticity of polymeric gels has been investigated. A commercial sample of a two-part poly(dimethyl siloxane) (PDMS) dielectric gel was used. The PDMS was cured around two flexible electrodes 5 mm apart while a mixture of PDMS with solvent was cured between the electrodes. The solvents were either silicone oil or an ER fluid composed of crosslinked poly(ethylene oxide) (PEO) particles in silicone oil. The mixtures investigated were 90/10, 60/40, 50/50, 40/60, 10/90 PDMS/solvent. Upon application of a 6.2 kV/cm DC electric field the gel was reversibly compressed. The time response of the gel was < 100 ms. In a 3 kV/cm, 1 Hz, AC electric field the gel was alternatingly compressed and expanded at twice the applied frequency. Above 15 Hz, the gel was only compressed. The smaller the PDMS/ER fluid ratio, the larger the response of the gel to the electric field. A small electromechanical actuator has been created using the 60/40 PDMS/ER fluid mixture.

[K32.43] Cross-linking and Phase Separation in a Thermoreversible Gel: Thermal Sol-to-gel Transition and Structure Factor

Using computer simulation, we study the evolution of gel and microgel particles as cross-linking and phase separation compete. A mixture of monomers and solvent of concentration C_p and C_s respectively is considered on a smple cubic lattice. A monomer is modelled by a polymer chain of length n while a solvent by a point-particle. Nearest neighbor polymer-polymer attractive, polymer-solvent repulsive, and solvent-solvent attractive interactions are considered. Monomers, solvent, and microgel particles resulting from a chemical reaction execute their stochastic movement using Metropolis algorithm with a hopping rate inversely proportional to their mass. Molecules react with a certain rate of reaction (J_m) while a bond between the monomers is broken with a degree of reversibility (J_r). We examine the volume fraction of the gel, weight average degree of polymerization (WADP), correlation length, and structure factor as a function of temperature and evaluate corresponding critical exponents for sol-to-gel transition. Evolution of the structure factors for the fluctuation in the polymer-solvent concentration (S(k)) and the solvent-vacancy concentration (S_1(k)) are studied during the various stages of the growth which shows interesting characteristics as the rate of reaction and the temperature are varied.

[K32.44] Effect of Solvent on Sol-to-Gel Transition: Onset of Inhomogeneity.

A computer simulation model is used to study the effect of solvent on sol-to-gel transition. We consider bifunctional and tetrafunctional monomers of concentrations C_2 and C_4 respectively on a simple cubic lattice. A nearest neighbor interaction of strength J between the polymeric units is introduced to control the quality of solvent and move the polymers with the Metropolis algorithm. Each monomer and microgel particle is mobile with a hopping rate inversely proportional to their mass. These polymeric units attempt to react with their neighboring units with a certain rate of reaction. We study the fraction of the bonds, volume fraction of the gel, and weight average degree of polymerization as the reaction proceeds. Analysing these quantities near the gel point we evaluate their critical exponents for sol-to-gel transition. The evolution of the structure of gel networks is analyzed by collective structure factors. Due to competition between the effect of dilution and the coagulation of clusters, phase-separated gel network seems to emerge leading to inhomogeneities. Thus, the quality of solvent is very important in governing the morphology of the gel.

[K32.45] Could Entanglements be Viewed as a Blended Phase.

We present the resulls of an extensive investigation of the deformation behavior of an amorphous polymer, polycarbonate, and explain the results in terms of the interactive coupling between conformers belonging to interpenetrating coil-macromolecules. Our investigation of the deformational properties includes viscous behavior (both capillary and Dynamic shear viscosity), stress-strain tensile tests at various rates and temperatures, flexural dynamic data below Tg, for both quenched and aged PC, and PVT results from 1.42 Tg (K) down to room temperature. All the results are consistent with a picture of the amorphous state suggested by the EKNET model, in which coiled up macromolecules pack and interpenetrate when interacting with one another, to create an interactive phase which, in many respects, behave like a blended phase. The mechanisms of toughening and embrittlement through physical aging are described in terms of the continuity or segregation of the coil interfacial interactive phase, which defines "permanent" entanglements. Dynamic entanglements can be created while deforming the melt below Tl,l and are responsible for shear-thinning. However, the dynamic entanglements are not permanent since they are only the reflection of the cooperative nature of the deformation process in the rubbery state, which is strain rate dependent.

[K32.46] Entanglement Effects on the Dynamics of a 2.89 \times 10^6 MW Polysterene Solution in Mixed Type Flow

In this paper, we compare predictions from the reptation model of Doi-Edwards, including segmental stretch, with measured birefringence data generated in a co-rotating two-roll mill. We consider a 7.6 wt% polysterene solution of MW = 2.89 \times 10^6 and low polydispersity (M_w/M_n = 1.09) in a mixed styrene oligomer/toluene solvent, for which there is an average of approximately 10 entanglements per chain. Measurements are reported both for steady-flows and for start-up from rest, with two-color birefringence used to obtain transients of birefringence and orientation of the optic axes in the solution, and dynamic light scattering used to measure the velocity gradient as a function of time; both at the stagnation point of the flow. Comparisons are made with reptation model predictions by using the measured velocity gradient data as input to the model, which is then used to predict the expected birefringence and orientation angle. The results show direct evidence for the onset of steady-state chain-stretching; the existence of a region of strain-rate thining of the extensional viscosity (as inferred from the stress-optical relationship); and reasonably good agreement between data and model predictions.

[K32.47] Enhanced Translational Diffusion of 9,10-bis\/(phenylethynyl)anthracene (BPEA) in Polystyrene

We have used a holographic fluorescence recovery after photobleaching (FRAP) techanique to measure translational diffusion coefficients of tracer levels of 9,10-bis\/(phenylethynyl)anthracene (BPEA) in polystyrene. Values for the diffusion coefficient D_T ranged from 10^-8 to 10^-14 cm^2/sec over the temperature range T_g+90K to T_g (T_g = 373K). D_T has a considerably weaker temperature dependence than matrix viscosity \eta. In contrast, the rotational correlation time \tau _c for BPEA has the same temperature dependence as \eta. At T_g, translational diffusion of BPEA is enhanced over rotation by 2.4 decades. These results support the idea that spatially heterogeneous dynamics are responsible for enhanced translation and are an important feature of dynamics at T_g.

[K32.48] Classical Theory of Polymer Brushes

We derive for polymer brushes the limit of the self-consistent field equations in which all configurations other than the most probable are ignored. Results for the brush profile and polymer end distribution depend sensitively on the ratio of the characteristic brush height to the polymer radius of gyration. The theory of Milner et al.(S.T. Milner et al., Macromolecules 21), 2610 (1988) and Zhulina et al. (E.B. Zhulina et al., J. Colloid Interface Sci. 137), 495 (1990) is shown to correspond to the classical theory only in the limit in which this ratio diverges.

[K32.49] Microstructure of Celluloses Studied by Positron Annihilation

Positron Annihilation Lifetime (PAL) measurements have been performed on Avicel and Whatman celluloses and their ball-milled derivatives as well as cellulose acetates. Correlations between crystallinity and fractional microsctructures found. Combined studies using PAL and FTIR on deuterated celluloses and moisture sorptions will be presented.

[K32.50] Enhancement of Interfacial Adhesion Between PS and SAN Blends by In-situ Chemical Reaction

Interfacial adhesion between immiscible polymer blends plays an important role in both academic and industrial applications. The interfacial adhesion behavior between polystyrene (PS) and oxazoline functionalized styrene-acryloitile copolymers (SAN) were investigated using an interfacial adhesive layer of poly(styrene-co-vinyl phenol) copolymers. The adhesion was studied as a function of mol oxazoline content using the double cantilever apparatus, optical microscopy, secondary ion mass spectrometry (SIMS), and x-ray photoelectron spectrometry (XPS) in order to determine the failure mode of the joints. The results obtained showed that interfacial toughness was increased with increasing oxazoline content in SAN and an optimal composition of oxazoline was found for the enhancement interfacial adhesion between immiscible polymers.

[K32.51] A Neutron Reflection Study of Adsorbed Polyelectrolyte Random Copolymers in Mixed Solvent

The conformation of sulfonated polystyrene chains adsorbed onto a silicon surface were studied uisng neutron reflection in buffered solutions of different PH values, in toluene, and in mixtures of the polar and non-polar solvents. The results indicate slight swelling of the layer with decreasing PH in the pure buffered solutions and significant swelling in the pure toluene solution. In the mixed solvent a trapped toluene layer is observed at the Si interface. The concentration profiles in the different solvents of the layers will be compared with mean field theory predictions.

[K32.52] Dynamics of Polymers Under Confinenment

The dynamics of polymers confined at attractive surfaces and free standing films were investigated using dynamic SIMS. The lateral diffusion was measured by observing with AFM the decay in the amplitude of a surface corrugation on a one micron grating. The glass transition was studied using a thin film calorimeter adapted for polymers. The diffusion results will be correlated to the glass transition measurements.

[K32.53] Magnetic Nanopatterning in an Electric Field

Magnetic patterns on a nanometer scale were obtained by a novel sputtering technique using imcompatible polymer blends. Lateral asymmetry in the patterns was obtained by the application of an external magnetic field. The relevance of these patterns in the design of GMR devices will be demonstrated.

Part K of program listing