Stochastic Dynamics Simulations of n-Alkane Melts Confined between Solid Surfaces: Influence of Surface Properties and Comparison with Scheutjens-Fleer Theory

Abstract

Stochastic dynamics simulations of n-alkane melts (C13H28 and C28H58) confined between solid surfaces have been performed in order to study the influence of the surface structure and interactions on the structural and dynamic properties of the chain molecules at the interfaces. Moreover, these simulation results have been compared with the predictions of the Scheutjens-Fleer lattice theory in order to investigate the general applicability of the theory in predicting the conformational properties of real (atomistic) melt chains at the interfaces. The n-alkane chains are described as mass points (united atoms) linearly connected by rigid bonds and subjected to bond bending, torsional, and nonbonded interaction potentials. For repulsive surfaces, an atomistic, ordered surface was found to yield the same static and dynamic properties of the chains as a flat, structureless surface. The presence of a strongly attractive surface was found to increase layering of both monomers and entire n-alkane molecules at the surface. Chains with only ends strongly attractive to the surfaces (sticky ends) exhibited an increased probability of long tails and loops and a decreased probability of long trains. However, no significant change in the strong preference for trains comprised of entire molecules was seen. Comparison of neutral surface and sticky end simulations with Scheutjens-Fleer self-consistent-field lattice theory predictions revealed that the theory reproduces quite well the behavior of tails, loops, and trains seen from atomistic simulations of C28H58. © 1995, American Chemical Society. All rights reserved.