Monte Carlo study of local orientational order in a semiflexible polymer melt model

Abstract

To investigate the character of local chain packing in a globally amorphous polymer melt, Monte Carlo simulations were performed on model systems consisting of polymers confined to a diamond lattice. The necessary condition for the existence of locally ordered domains is shown to be the presence of local chain stiffness, which in these systems is manifested by the energetic preference of trans (t) over gauche (g) states. These locally parallel domains are not unique static structures but rather are defined only in a statistical sense and exist over a rather broad temperature range. The local domain structure appears to be insensitive to the molecular weight, provided that the chain length exceeds the domain size. It is also found that, to a very good approximation, within a given chain, two subchains belonging to two different domains are statistically independent. The local domain structure becomes enhanced, at fiied chain stiffness, by inclusion of attractive interactions between nonbonded nearest neighbors and/or by increasing the polymer density. The locally ordered melt is shown to be globally disordered over a broad temperature range, with the dimensions of an individual chain very close to those obtained from ideal chain statistics. Various quantities characterizing the character of local ordering in these model systems are examined, and the applicability of these results to real polymer systems is discussed.