UCLA

This thesis summarizes a collection of computational studies on glass relaxation and glass-forming ability using the methodology of molecular dynamic simulation and topological constraint theory. As out-of-equilibrium materials, glasses continually tend to relax toward the metastable supercooled liquid state. Glass relaxation can result in a non-reversible glass transition upon a cooling/reheating cycle. With the help of molecular dynamic simulation, we present a novel methodology combining thermal cycles and inherent configuration analysis to investigate the features of relaxation and glass transition reversibility. By considering three archetypical silicate glasses, viz., silica, sodium silicate, and calcium aluminosilicate, we show that, for all the glasses considered herein, the enthalpy relaxation can be well described by mode-coupling theory.[1] Further, we demonstrate the existence of a decoupling between enthalpy and volume relaxation and show that enthalpy relaxation results in a non-reversible glass transition—the degree of non-reversibility being strongly system-specific. In addition to glass relaxation, we also investigate the narrow glass-forming ability window of calcium silicate glass which exhibits an interesting connection with the average number of constraints. By performing molecular dynamic simulations on calcium silicate glasses with a series of CaO composition, we compute the number of constraints as a function of CaO composition and illustrate the strong dependence between glass-forming ability and the rigidity of glass network.