Internal viscosity in polymer chains: A critical analysis

Abstract

The theory relating internal viscosity to nonequilibrium statistics of chain rotational states is critically reinvestigated, to obtain a comprehensive formulation valid in the whole range of the Fourier normal modes, not necessarily under Θ-conditions. The internal viscosity force acting on a given atom is linearly related with the local strain rate or, more precisely, with the time rate of change of the local configurational free energy. An error by a factor 2 in the previously proposed numerical coefficient of the internal viscosity is pointed out. A simplified comparison with other internal viscosity theories deriving from the hindered rotation concept is carried out on the basis of linear Langevin equations of motion valid for collective chain modes. It is shown that the present theory obeys the twofold requirement of leading to a physically needed upper limit of the rate of propagation along the chain as well as to a spectrum of relaxation times in satisfactory agreement with experimental data.