Publications

Journal of Polymer Science, Part B: Polymer Physics

Sides, Scott W.; Grest, Gary S.; Stevens, Mark J.; Plimpton, Steven J.

The adhesion between a glassy polymer melt and substrate is studied in the presence of end-grafted chains chemically attached to the substrate surface. Extensive molecular dynamics simulations have been carried out to study the effect of the areal density Σ of tethered chains and tensile pull velocity v on the adhesive failure mechanisms. The initial configurations are generated using a double-bridging algorithm in which new bonds are formed across a pair of monomers equidistant from their respective free ends. This generates new chain configurations that are substantially different than the original two chains such that the systems can be equilibrated in a reasonable amount of cpu time. At the slowest tensile pull velocity studied, a crossover from chain scission to crazing is observed as the coverage increases, while for very large pull velocity, only chain scission is observed. As the coverage increases, the sections of the tethered chains pulled out from the interface form the fibrils of a craze that are strong enough to suppress chain scission, resulting in cohesive rather than adhesive failure. © 2003 Wiley Periodicals, Inc.

Journal of Chemical Physics

Auhl, Rolf; Everaers, Ralf; Grest, Gary S.; Kremer, Kurt; Plimpton, Steven J.

Equilibrated melts of long chain polymers were prepared. The combination of molecular dynamic (MD) relaxation, double-bridging and slow push-off allowed the efficient and controlled preparation of equilibrated melts of short, medium, and long chains, respectively. Results were obtained for an off-lattice bead-spring model with chain lengths up to N=7000 beads.

Proposed for publication in Powder Technology.

Grest, Gary S.; Landry, James W.; Grest, Gary S.; Plimpton, Steven J.

Abstract not provided.

Journal of Physical Chemistry B

Chandross, M.; Webb, Edmund B.; Grest, Gary S.; Martin, Marcus G.; Thompson, Aidan P.; Roth, M.W.

We present the results of Molecular Dynamics and Monte Carlo simulations of n-butane and isobutane in silicalite. We begin with a comparison of the bulk adsorption and diffusion properties for two different parameterizations of the interaction potential between the hydrocarbon species, both of which have been shown to reproduce experimental gas-liquid coexistence curves. We examine diffusion as a function of the loading of the zeolite, as well as the temperature dependence of the diffusion constant at loading and for infinite dilution. Both force fields give accurate descriptions of bulk properties. We continue with simulations in which interfaces are formed between single component gases and the zeolite. After reaching equilibrium, we examine the dynamics of exchange between the bulk gas and the zeolite. In particular, we examine the average time spent in the adsorption layer by molecules as they enter the zeolite from the gas in an attempt to probe the microscopic origins of the surface barrier. The microscopic barrier is found to be insignificant for experimental systems. Finally, we calculate the permeability of the zeolite for n-butane and isobutane as a function of pressure. Our results underestimate the experimental results by an order of magnitude, indicating a strong effect from the surface barrier in these simulations. Our simulations are performed for a number of different gas temperatures and pressures, covering a wide range of state points.