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Kenneth S. Schweizer - One of the best experts on this subject based on the ideXlab platform.
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many body effects on the phase separation and structure of dense Polymer Particle melts
Journal of Chemical Physics, 2008Co-Authors: Lisa M Hall, Kenneth S. SchweizerAbstract:Liquid state theory is employed to study phase transitions and structure of dense mixtures of hard nanoParticles and flexible chains (Polymer nanocomposites). Calculations are performed for the first time over the entire compositional range from the Polymer melt to the hard sphere fluid. The focus is on Polymers that adsorb on nanoParticles. Many body correlation effects are fully accounted for in the determination of the spinodal phase separation instabilities. The nanoParticle volume fraction at demixing is determined as a function of interfacial cohesion strength (or inverse temperature) for several interaction ranges and nanoParticle sizes. Both upper and lower critical temperature demixing transitions are predicted, separated by a miscibility window. The phase diagrams are highly asymmetric, with the entropic depletion-like lower critical temperature occurring at a nanoParticle volume fraction of ∼10%, and a bridging-induced upper critical temperature at ∼95% filler loading. The phase boundaries are ...
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dynamic yielding shear thinning and stress rheology of Polymer Particle suspensions and gels
Journal of Chemical Physics, 2005Co-Authors: Vladimir Kobelev, Kenneth S. SchweizerAbstract:The nonlinear rheological version of our barrier hopping theory for Particle-Polymer suspensions and gels has been employed to study the effect of steady shear and constant stress on the alpha relaxation time, yielding process, viscosity, and non-Newtonian flow curves. The role of Particle volume fraction, Polymer-Particle size asymmetry ratio, and Polymer concentration have been systematically explored. The dynamic yield stress decreases in a Polymer-concentration- and volume-fraction-dependent manner that can be described as apparent power laws with effective exponents that monotonically increase with observation time. Stress- or shear-induced thinning of the viscosity becomes more abrupt with increasing magnitude of the quiescent viscosity. Flow curves show an intermediate shear rate dependence of an effective power-law form, becoming more solidlike with increasing depletion attraction. The influence of Polymer concentration, Particle volume fraction, and Polymer-Particle size asymmetry ratio on all properties is controlled to a first approximation by how far the system is from the gelation boundary of ideal mode-coupling theory (MCT). This emphasizes the importance of the MCT nonergodicity transition despite its ultimate destruction by activated barrier hopping processes. Comparison of the theoretical results with limited experimental studies is encouraging.
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contact aggregation bridging and steric stabilization in dense Polymer Particle mixtures
Macromolecules, 2005Co-Authors: Justin B Hooper, Kenneth S. SchweizerAbstract:A detailed computational study of the potential of mean force between a pair of spherical Particles dissolved in a homoPolymer melt has been performed using microscopic liquid state theory. The rol...
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microscopic theory of gelation and elasticity in Polymer Particle suspensions
Journal of Chemical Physics, 2004Co-Authors: Yenglong Chen, Kenneth S. SchweizerAbstract:A simplified mode-coupling theory (MCT) of ergodic-nonergodic transitions, in conjunction with an accurate two-component Polymer reference interaction site model (PRISM) theory for equilibrium structural correlations, has been systematically applied to investigate gelation, localization, and elasticity of flexible Polymer-hard Particle suspensions. The Particle volume fraction at the fluid-gel transition is predicted to depend exponentially on reduced Polymer concentration and size asymmetry ratio at relatively high colloid concentrations. In contrast, at lower Particle volume fractions, a power-law dependence on Polymer concentration is found with effective exponents and prefactors that depend systematically on the Polymer/Particle size ratio. Remarkable power-law and near universal scaling behavior is found for the localization length and elastic shear modulus. Multiple experiments for gel boundaries and shear moduli are in good agreement with the no adjustable parameter theory. The one exception is the absolute magnitude of the shear modulus which is strongly overpredicted, apparently due to nonequilibrium dense cluster formation. The simplified MCT-PRISM theory also captures the qualitative aspects of the weak depletion-driven "glass melting" phenomenon at high Particle volume fractions. Calculations based on an effective one-component model of structure within a low Particle volume fraction framework yield qualitatively different features than the two-component approach and are apparently all in disagreement with experiments. This suggests that volume fraction and size asymmetry dependent many-body screening of Polymer-mediated depletion attractions at finite Particle concentrations are important.
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phase separation in suspensions of colloids Polymers and nanoParticles role of solvent quality physical mesh and nonlocal entropic repulsion
Journal of Chemical Physics, 2003Co-Authors: Yenglong Chen, Kenneth S. Schweizer, Matthias FuchsAbstract:Analytic and numerical microscopic integral equation theory for Polymer–Particle suspensions is employed to investigate the dependence of fluid–fluid phase separation on size asymmetry, solvent quality, and higher order Polymer–Polymer interactions. For athermal good solvents, our prior novel prediction of enhanced miscibility with increasing (decreasing) Polymer (Particle) size is found not to be fundamentally tied to physical mesh formation or strong Polymer-induced colloid clustering. Rather, the key is a proper treatment of the Polymer second virial coefficient, which is sensitive to how chains organize in the empty space between Particles. The origin of the qualitative error made by classic mean-field theories for the shifting of phase boundaries with size asymmetry is established. The phase separation behavior predicted by integral equation theory for ideal Polymers is completely different than the athermal case for all size asymmetries and Particle volume fractions, thereby establishing the remarka...
Robert E Tuzun - One of the best experts on this subject based on the ideXlab platform.
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computational simulation of Polymer Particle structures vibrational normal modes using the time averaged normal coordinate analysis method
Polymer, 2003Co-Authors: Bryan C Hathorn, Bobby G Sumpter, D W Noid, Robert E Tuzun, Chao YangAbstract:The structures composed of individual Polymer nanoParticles are simulated using a molecular dynamics technique. Structures composed of model polyethylene Particles consisting of between 3000 and 24,000 monomer units are paired into dimers in a molecular dynamics simulation. The vibrational motion of the Polymer Particle structures corresponding to the stretching vibration between Particles is studied using the time averaged normal coordinate analysis method. The data are fit to an empirical formula based on the expected scaling of the force constants with the surface contact area, yielding a formula which could be extrapolated to large Particle structures which can be experimentally generated.
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large scale normal coordinate analysis of macromolecular systems thermal properties of Polymer Particles and crystals
Journal of Physical Chemistry B, 2000Co-Authors: Kazuhiko Fukui, Bobby G Sumpter, D W Noid, Chao Yang, Robert E TuzunAbstract:Using novel modifications to a sparse matrix solver (ARPACK), a complete spectral analysis has been achieved for a 6,000 atom Polymer system involving all 18,000 degrees of freedom. A comparison of the thermal properties and spectra of an annealed Polymer Particle and crystal is presented. The density of states spectrum g({omega}) shows a higher number of low-frequency modes for the Polymer Particle, which results in a higher heat capacity at low temperature. The distribution of energy level spacing shows some resemblance to that exhibited by random matrices. Finally, the displacement of low-frequency eigenvectors is shown to have a larger amplitude on the surface than in the interior of either the Particle or crystal.
Chao Yang - One of the best experts on this subject based on the ideXlab platform.
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computational simulation of Polymer Particle structures vibrational normal modes using the time averaged normal coordinate analysis method
Polymer, 2003Co-Authors: Bryan C Hathorn, Bobby G Sumpter, D W Noid, Robert E Tuzun, Chao YangAbstract:The structures composed of individual Polymer nanoParticles are simulated using a molecular dynamics technique. Structures composed of model polyethylene Particles consisting of between 3000 and 24,000 monomer units are paired into dimers in a molecular dynamics simulation. The vibrational motion of the Polymer Particle structures corresponding to the stretching vibration between Particles is studied using the time averaged normal coordinate analysis method. The data are fit to an empirical formula based on the expected scaling of the force constants with the surface contact area, yielding a formula which could be extrapolated to large Particle structures which can be experimentally generated.
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large scale normal coordinate analysis of macromolecular systems thermal properties of Polymer Particles and crystals
Journal of Physical Chemistry B, 2000Co-Authors: Kazuhiko Fukui, Bobby G Sumpter, D W Noid, Chao Yang, Robert E TuzunAbstract:Using novel modifications to a sparse matrix solver (ARPACK), a complete spectral analysis has been achieved for a 6,000 atom Polymer system involving all 18,000 degrees of freedom. A comparison of the thermal properties and spectra of an annealed Polymer Particle and crystal is presented. The density of states spectrum g({omega}) shows a higher number of low-frequency modes for the Polymer Particle, which results in a higher heat capacity at low temperature. The distribution of energy level spacing shows some resemblance to that exhibited by random matrices. Finally, the displacement of low-frequency eigenvectors is shown to have a larger amplitude on the surface than in the interior of either the Particle or crystal.
Toshiyuki Tamai - One of the best experts on this subject based on the ideXlab platform.
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formation of metal nanoParticles on the surface of Polymer Particles incorporating polysilane by uv irradiation
Langmuir, 2008Co-Authors: Toshiyuki Tamai, Mitsuru Watanabe, Yoshiro Hatanaka, Hiroyuki Tsujiwaki, Noboru Nishioka, Kimihiro MatsukawaAbstract:Polystyrene Particles incorporating poly(methylphenylsilane) (PMPS) were synthesized by miniemulsion Polymerization. UV irradiation of the emulsion under air in the presence of metal salts such as HAuCl4·4H2O, AgNO3, and Na2PdCl4 led to the formation of metal nanoParticles on the surface of Polymer Particles; thus, metal nanoParticle/Polymer hybrid Particles were obtained. The structures of the hybrid Particles were confirmed by the surface plasmon resonance band and transmission electron microscopy images. The formation of metal nanoParticles depended on the functional groups and charge on the surface of the Polymer Particle. The metal nanoParticles were formed due to the reduction of metal ions, accompanied by the oxidation of PMPS. The interaction between the surface of the Polymer Particle and the metal ions plays an important role in the formation of the metal nanoParticle.
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sol gel reaction in acrylic Polymer emulsions the effect of Particle surface charge
Langmuir, 2007Co-Authors: Mitsuru Watanabe, Toshiyuki TamaiAbstract:Acrylic Polymer−silica hybrid emulsions were synthesized from both anionic and cationic Polymer emulsions by simple post-addition of tetraethoxysilane as a silica precursor. Solvent resistance of the films from the hybrid emulsions and the ζ-potential of the hybrid emulsions suggested the different forms of silica components in each hybrid emulsion. Thermal gravimetric analysis, 29Si NMR measurements, and transmission electron microscope observations revealed that the hybrid emulsion from the anionic Polymer emulsion was a mixture of anionic Polymer Particles and homogeneously dissolved silicate oligomer−Polymer. On the contrary, the hybrid emulsion from cationic Polymer emulsion consisted of Polymer core−silica shell Particles. The electrostatic interaction between the cationic Polymer Particle surface and the silicate would be responsible for the accumulation of the silicate onto the Particle surface, leading to the silica shell layer formation. The sol−gel condensation reaction of silicate in the acidi...
Bobby G Sumpter - One of the best experts on this subject based on the ideXlab platform.
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computational simulation of Polymer Particle structures vibrational normal modes using the time averaged normal coordinate analysis method
Polymer, 2003Co-Authors: Bryan C Hathorn, Bobby G Sumpter, D W Noid, Robert E Tuzun, Chao YangAbstract:The structures composed of individual Polymer nanoParticles are simulated using a molecular dynamics technique. Structures composed of model polyethylene Particles consisting of between 3000 and 24,000 monomer units are paired into dimers in a molecular dynamics simulation. The vibrational motion of the Polymer Particle structures corresponding to the stretching vibration between Particles is studied using the time averaged normal coordinate analysis method. The data are fit to an empirical formula based on the expected scaling of the force constants with the surface contact area, yielding a formula which could be extrapolated to large Particle structures which can be experimentally generated.
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large scale normal coordinate analysis of macromolecular systems thermal properties of Polymer Particles and crystals
Journal of Physical Chemistry B, 2000Co-Authors: Kazuhiko Fukui, Bobby G Sumpter, D W Noid, Chao Yang, Robert E TuzunAbstract:Using novel modifications to a sparse matrix solver (ARPACK), a complete spectral analysis has been achieved for a 6,000 atom Polymer system involving all 18,000 degrees of freedom. A comparison of the thermal properties and spectra of an annealed Polymer Particle and crystal is presented. The density of states spectrum g({omega}) shows a higher number of low-frequency modes for the Polymer Particle, which results in a higher heat capacity at low temperature. The distribution of energy level spacing shows some resemblance to that exhibited by random matrices. Finally, the displacement of low-frequency eigenvectors is shown to have a larger amplitude on the surface than in the interior of either the Particle or crystal.