Efficient computational models and methods for investigating local polymer dynamics

Abstract

Local Phenomena related to the isomerization of torsional angles in polymers are studied using computational tools with emphasis on the problem of efficiency. Molecular and Brownian Dynamics, Dynamic Rotational Isomeric States Model, Cooperative Kinematics methods are utilized to study various aspects of local dynamics. The results provide a clear picture of local phenomena: Disturbances along the chain are accommodated by local motion confined to a segment of ten bonds approximately. Mainly, large and small amplitude torsions in the neighboring bonds, spatial reorientation of bonds, and translational motion of chain atoms occur. The exact mechanism of relaxation behavior is dictated by the geometry of the backbone bonds. All of the mentioned mechanisms are composed of the combined effect of rotameric jumps and librational motions. Coupling between the two is particularly enhanced during the passage over the rotation barrier. It is now known that librational motion which are generally assumed to be decoupled from the slow relaxation processes in polymer chains in many studies in literature are not random. On the contrary, they are highly correlated so that local chain direction is preserved and the reorientations induced by isomeric jumps are accommodated without significant distortion of chain conformation on a large scale.