On the Effect of Internal Viscosity

The characteristic viscosity (6.22) is of special interest in the study of the influence of intramolecular friction on the dynamics of a macromolecule in a viscous liquid. At w — oo, characteristic viscosity can be written as 

Experimental studies indicate (Cooke and Matheson 1976, Noordermeer et al. 1975) that the limiting characteristic viscosity for a given polymer-homologous series is independent of the length of macromolecule and the type of solvent. Taking into account that t AT , n AT-1 and yq M e, one can find the relation 

The independence of the limiting characteristic viscosity on the type of solvent means that cpi is independent of the viscosity of the solvent, that is the dimensional characteristic of the internal friction of the macromolecule Cyi is proportional to the viscosity of the solvent and the internal friction is not solely internal. The conclusion that the solvent contributes significantly to the intramolecular viscosity was reported by Schrag (1991), and was dubbed as the solvent modification effect . 

The fact that the value of the characteristic viscosity at high frequencies is not zero indicates the existence of intramolecular (taking into account the solvent molecules) relaxation processes with relaxation times smaller than the reciprocal of the frequency of the measurement. The true limiting value is naturally zero and experiments sometimes reveal a step at a frequency uj which indicates the occurrence of a relaxation process with a relaxation time r a -1 which is compatible to the times of the deformation of a system. This phenomenon may be described by including the relaxing intramolecular viscosity, as it was done by Volkov and Pokrovskii (1978). 

One uses expression (6.18) for the stress tensor in which the memory function can be chosen in the simplest way 

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