Differences in thermal conformation fluctuation between two models for semiflexible chains

Abstract

Differences in thermal conformation fluctuation, particularly in longitudinal deformation, have been examined for two semiflexible chain models of the longitudinally stiff (LS) and the longitudinally flexible (LF) chains. The LF chain exhibits fairly large, longitudinal conformation fluctuations: The mean fluctuation of the tangent-vector length amounts to 44% of its average. General formulas for the correlation functions of various quantities related to chain bending and stretching are given for the LF chain. It is shown that, though the motion of an LF chain can be decomposed into mutually independent normal modes, the longitudinal stretching and transverse bending motions are made in some correlated manner. Depending on its contour shape and external forces, a complex distribution of internal stresses is produced in each cross section of an LS chain. It varies along the chain, which ensures the nearly inextensible nature of the LS chain. It is concluded that, if the motion of an LS chain is described by a series of normal modes, their amplitudes will change with time in a strongly correlated manner quite distinct from the case of LF chains.