Static properties of homopolymer melts in confined geometries determined by Monte Carlo simulation

The static properties of a homopolymer melt between energetically neutral walls are studied as a function of the degree of confinement (plate spacing) and polymer molecular weight. The cooperative motion lattice model is used and allows all calculations to be performed at full occupancy (i.e., at a volume fraction of 1); chain lengths varying from 384 to 24 are examined. Properties investigated include the magnitude of the end-to-end vector, the radius of gyration, and components of the end-to-end vector. In addition, orientation effects and the distribution of chain ends are also calculated. As the chains are confined, the end-to-end vectors align parallel to the walls beginning at a value of about twice the unconstrained value of the radius of gyration, regardless of the molecular weight. For values less than this, chain conformations are distorted and the magnitude of the average end-to-end vector and radius of gyration increase. The components of the end-to-end vector parallel and perpendicular to the walls are considered; in the cases of confinement, it is seen that there is a universal scaling relationship between the parallel component of the end-to-end vector and the plate spacing. The parallel component increases with the decreasing plate spacing according to approximately a one-sixth power ([r(2)](parallel to)(1/2)similar to L-1/6). Chain ends are most likely to be in the vicinity of one of the walls due to entropic constraints.