Entropy Theory and Glass Transition: A Test by Monte Carlo Simulation

This article reviews the results of a test of the Gibbs-DiMarzio theory by Monte Carlo Simulation. The simulation employed the bond-fluctuation model on a simple cubic lattice. This model incorporates two kinds of interactions: the excluded volume interaction among all monomers of the melt and an internal energy of the chains, which favors large bonds and makes the chains stiffen with decreasing temperature. The stiffening of the chains leads to an increase of their volume requirements, which competes with the packing constraints at low temperatures. This competition strongly slows down the structural relaxation of the melt and induces the glassy behavior. The model therefore takes into account the main opposing forces which the Gibbs-DiMarzio theory makes responsible for the glass transition. For this model the entropy was calculated from the internal and the free energy (derived from the chemical potential and the single chain partition function) and compared with various theoretical predictions: the Gibbs-DiMarzio theory, a theory by Flory for semiflexible polymers and an extended theory by Wittmann considering Milchev's criticism on Flory's calculation. The latter extended theory provides the best description of the simulation data.