CROSSOVER-BEHAVIOR IN THE VISCOSITY OF SEMIFLEXIBLE POLYMERS - INTERMOLECULAR INTERACTIONS AS A FUNCTION OF CONCENTRATION AND MOLECULAR-WEIGHT

A simple relation is presented for the viscosity of isotropic solution s of flexible, semiflexible and rodlike chains over a range of concent ration from dilute solutions to undiluted polymer, chain contour lengt h L and persistence length (a) over cap. The expression is designed to account for the separate effects of screening of thermodynamic and hy drodynamic interactions, and the onset of intermolecular chain entangl ements under Flory theta solvent conditions, or in ''good'' solvents, for which intramolecular excluded volume is important in dilute soluti ons. The relation includes a revised (dimensionless) Fox parameter <(X )over tilde (c)> that determines the onset of intermolecular entanglem ents, where <(X)over tilde (c)> = pi N-A rho L(c) (a) over cap/3M(L) f or semiflexible polymers with (a) over cap much less than L, with rho the polymer density, M(L) the mass per unit length of the chain, and L (c) the value of L for the onset of entanglement effects in undiluted polymer; <(X)over tilde (c)> approximate to 100 for a number of system s, including rodlike chains. (C) 1996 Society of Rheology.