Structure dependent hydrodynamic properties and brownian motion of polymeric molecules

Abstract

Pending problems in polymer dynamics are treated, particularly regarding the relevance of the concept of internal viscosity for kinetically flexible chains. The discussion is based on the assumption that local non-diffusional (possibly cooperative) segmental rearrangements coexist with the fastest diffusional ones; it makes use of the author's limiting model that permits one to account for one type of local movement, either diffusional or non-diffusional. Association of internal viscosity coefficients with the normal modes is shown to be justified by the stochastic approach to polymer dynamics. The η0-independent internal viscosity parameter can be expressed in terms of local dynamical characteristics. Stress-tensor symmetry follows from the mode-dependence of the internal viscosity coefficients when the rotational velocity of the chain is calculated as if it were rigidified. Comparison with experimental results obtained by various techniques confirms that η0-independent internal viscosity, hence local dynamics, may be manifested in the longest relaxation times. Thus, it is also confirmed that local non-diffusional processes may contribute to the renewal of conformations. The model further allows for η0-proportional internal viscosity. It is however suggested that the latter one arises for the most part from diffusional movements which cannot be accounted for by the sole consideration of the Rouse-modes. A tentative description of the Brownian motion of the chain and of its deformation in a high frequency shearing gradient is proposed that would qualitatively explain both that the η 0-independent internal viscosity must vanish at high frequency and that the limiting value [η'] ∞ of the intrinsic viscosity is nearly molecular weight independent