Thermodynamics molecular glass structure

It would be an advantage to have a detailed understanding of the glass transition in order to get an idea of the structural and dynamic features that are important for photophysical deactivation pathways or solid-state photochemical reactions in molecular glasses. Unfortunately, the formation of a glass is one of the least understood problems in solid-state science. At least three different theories have been developed for a description of the glass transition that we can sketch only briefly in this context the free volume theory, a thermodynamic approach, and the mode coupling theory. 

Navrotsky A., Geisinger K. L., McMillan R, and Gibbs G. V. (1985). The tetrahedral framework in glasses and melts Inferences from molecular orbital calculations and implications for structure, thermodynamics and physical properties. Phys. Chem. Minerals, 11 284-298. 

Thus, one could conclude that the molecular structure of glassy polymers has only a small effect on the relaxation processes associated with the nonequilibrium thermodynamic state of the glasses. 

A fundamental property that determines the state of a reacting system is its extent of cure or chemical conversion (a). Several papers have shown that there is a unique relationship between the glass-transition temperature (Tg) and a that is independent of cure temperature and thermal history. This may imply that molecular structures of materials cured with different histories are the same or that the changes in molecular structure do not affect Tg. There are generally accepted to be two approaches to modelling glass-transition-conversion relationships, namely thermodynamic and viscoelastic approaches. These are summarized in Table 3.8. 

The goal of the work reported here was to devise a theory that predicts the polar/nonpolar phase separation as a favorable thermodynamic process. In addition, the effects of each of the physicochemical forms on the thermodynamic and structural characteristics of the biphasic material were sought. The current molecular model was not developed to predict mechanical or thermal behavior of ionomers. Hence, properties like glass transition and melt temperatures, storage, and shear moduli cannot be determined from the current model. We must also stress that this modeling work is still in its infancy. As such, it has used several tenuous assumptions that must be tested. The formalism is a start, but not the end, to devising a comprehensive treatment of ionomeric structure. 

---