Significance of the intramolecular degrees of freedom on the glass-forming process

The Adam-Gibbs theory of the glass-transition is extended at its molecular level. An expression for the number of configurations in the cooperatively rearranging region, which makes the macroscopic and molecular Adam-Gibbs equations compatible, is obtained. The number of configurations in the cooperatively rearranging region depends on the method for estimating the contribution of the vibration entropy to the entropy of the liquid. Two ways of extracting the vibration component from the entropy of the liquid have been used. In the first, the configuration entropy is regarded as the difference between those of the liquid and the crystal, and the second as the difference between the entropies of the liquid and the glass. In both cases the obtained number of configurations is larger than w(z)=2, as accepted by Adam and Gibbs. The measured number of configurations was found to increase with the size of the cooperatively rearranging regions or the kinetic fragility of the liquids. This indicates that the cooperatively rearranging region is a flexible, with internal rearranging, dynamical cluster. As the basic kinetic units in the Adam-Gibbs cooperatively rearranging region have been identified as fragments of molecules known in thermodynamics as "beads," it is concluded that the intramolecular degrees of freedom arc substantial for avoiding the crystallization, during the cooling and forming of the glass.