Dynamic Monte Carlo simulations of isolated polymer chains using lattice models: 1) chain terminally attached to an infinite plane, 2) shape fluctuations

Conformational and dynamic properties of isolated polymer chains were studied under two distinct conditions. Under one condition, conformational changes were studied for a chain terminally attached to a flat, impenetrable surface. The second condition looked at a free chain viewed as ellipsoidal in shape. Conformational fluctuations of the ellipsoid were studied by separating the motions into three rigid rotations (one for each axis) and three dilation and contraction motions (one for each axis). Both studies were Monte Carlo computer simulations of polymer chains with different molecular weights, by using either a simple cubic or face centered cubic lattice model. In both cases, the polymer chains were assumed to be a collection of connected statistical segments called beads, each representing several repeat units. The terminally attached chains were found to be somewhat enlarged if the beads were assumed to occupy space (like hard spheres) and they were found to have significantly lower mobility than corresponding free chains. However, both size and mobility of terminally attached chains did seem to have the same molecular weight dependence as corresponding free chains. Using the ellipsoidal model for free chains showed the chain to be highly anisotropic and that the order of increasing size was the order of decreasing mobility with respect to dilations and contractions, for each of the axes of the ellipsoid. These dilation and contraction motions were shown to be closely related to the first three normal modes for free chains.