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Expanded ensemble density-of-states simulations and a connectivity altering algorithm are used to investigate the effective interactions that arise between nanoparticles suspended in polymer solutions. Our calculations with systems of long polymeric chains reveal oscillations in the effective polymer-induced interactions between the particles, even at low concentrations. The range of these interactions is considerably longer than originally anticipated, and their origin is traced back to the chain-end effects and density fluctuations that were absent in previous treatments of these systems. [ABSTRACT FROM AUTHOR]

The structure of polymers in the vicinity of spherical colloids is investigated by Monte Carlo simulations and integral equation theory. Polymers are represented by a simple bead-spring model; only repulsive Lennard-Jones interactions are taken into account Using advanced trial moves that alter chain connectivity, depletion and packing effects are analyzed as a function of chain length and density, both at the bond and the chain level. Chain ends segregate to the colloidal surface and polymer bonds orient parallel to it. In the dilute regime, the polymer chain length governs the range of depletion and has a negligible influence on monomer packing in dense polymer melts. Polymers adopt an ellipsoidal shape, with the larger axis parallel to the surface of the particle, as they approach larger colloids. The dimensions are perturbed within the range of the depletion layer. [ABSTRACT FROM AUTHOR]

We have studied the kinematics and rheological properties of undiluted polymers by modeling the fluids as a collection of interacting Kramers freely jointed bead–rod chains with anisotropic friction using Brownian dynamics simulations. The anisotropic friction depends on the instantaneous configuration of the system. The resulting stochastic differential equations have multiplicative noise. The correlation of the ‘‘Langevin’’ Brownian forces appearing in these equations turns out to be anisotropic as well. The excluded volume effect, often ignored in kinetic theory, plays an important role in the behavior of short polymer chains. The chain kinematics may be distorted in its absence. In this work, we also discuss the effects of two types of excluded volume (EV) forces (hard-sphere and soft-repulsive forces) on rheological properties of concentrated polymer solutions. [ABSTRACT FROM AUTHOR]

The assembly of lamella-forming block copolymer blend thin films on chemically nanopatterned striped surfaces was monitored in real time with small angle x-ray scattering (SAXS) in transmission mode. The strongest diffraction from the assembled grating structure was detected after 4.5 min of annealing as the temperature was ramped from 100 to 240 °C at a rate of about 20 °C/min. Real-space images were also obtained from samples annealed for specific times using top-down scanning electron microscopy (SEM) and this identified structures formed during annealing that are unique to the block copolymer blends. The data are compared to previously reported SEM and molecular simulation studies with pure block copolymers. Because it can be used in real time and probes the entire film thickness, transmission SAXS proved to be a useful tool for better understanding the block copolymer annealing process. [ABSTRACT FROM AUTHOR]