A Nonlinear Viscoelastic Model for Glassy Polymers

The relaxation of polymer molecules near the glass transition temperature is thought to be enabled through the cooperative motion of the molecular segments, or the conformers. According to the theory of Adam and Gibbs, the domain size for cooperativity is inversely proportional to the configurational entropy, and it grows larger as the temperature is lowered. The apparent activation energy for the mean relaxation time is predicted to be proportional to the critical domain size, and this result is in quantitative agreement with the Vogel-Fulcher and WLF equations.