Intermolecular cooperativity in dielectric and viscoelastic relaxation

Abstract

A model for the glass transition which incorporates inter-molecular cooperativity is proposed. A domain of cooperativity is defined as a group of segments that must undergo relaxation simultaneously. As the density is increased by changes in temperature or pressure, the configurational entropy in the condensed state decreases much more rapidly than it does in isolated chains. The resulting equation is similar to the well-known Adam-Gibbs equation, although changes in the domain size, z, and the entropy are due primarily to intermolecular hindrance of the relaxation of individual conformers. A spectrum of relaxation times derived from the domain size distribution is similar to the KWW equation near the characteristic time-scale, but fits data better at high frequencies. The temperature dependence of the width of the spectrum is explained from the dependence of the temperature coefficients on the domain size.