Molecular surfaces: An advantageous starting point for the description of composition-dependent viscosities applied to polymer solutions

The viscosity of polymer/solvent systems is modeled as a function of compos ition under the premises that the dissipation of energy is taking place at the molecular interfaces and that the friction between solvent and solute v aries with composition due to a change in the flow mechanism (drainage of c oils). The simple expression obtained in this manner contains three system- specific parameters: a geometric factor gamma, which accounts for the diffe rences of the surface to volume ratios of the components; a hydrodynamic pa rameter alpha, which measures the friction between solute and solvent in th e case of fully draining polymer coils; and beta, which corrects for change s in the friction between unlike molecules resulting from collective motion s owing to limited draining. Experimental data published for 12 poly(dimeth ylsiloxane)/pentamer mixtures can be represented quantitatively by this rel ation; moreover the knowledge of the three system-specific parameters permi ts the calculation of intrinsic viscosities, and the molecular weight depen dencies of gamma and alpha yield the entangle molecular weight of the polym er. (C) 1999 John Wiley & Sons, Inc.