Thermodynamic and dynamic properties of glass-forming materials under high pressure or with strong interactions



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The relationship between equilibrium dynamics and thermodynamics of glass-forming materials is studied through experimental investigations and theoretical modeling in the domains of temperature, pressure, intermolecular interactions. In this dissertation, several glass-forming systems are studied, including pharmaceutical and polymeric glasses. In the case of pharmaceuticals, the glass transition temperature (Tg) for synergistic co-amorphous pharmaceutical mixtures is successfully described as a function of composition using the activity coefficient models with the physical meaning of the parameters maintained. This approach contrasts with the common approach, that is using the Gordon-Taylor and Kwei equations and fitting the parameters, so that the physical meaning of the parameters is compromised.

In addition, in this dissertation, the configurational entropy, enthalpy, internal energy, free energy, along with the free volume, are examined for their abilities to reduce the temperature- and pressure-dependent segmental relaxation times data for polymers with no bias imposed by the assumption of a linear reciprocal dependence or other specific modeling forms. This model-free method demonstrates a strongly material-dependent scaling ability for these configurational thermodynamic properties, which sheds doubt on the idea that there is a predominant thermodynamic property that governs the relaxation time.

Finally, the structural recoveries of pressure-densified and, for the first time, pressure-expanded glasses are experimentally investigated using pressurizable dilatometry. The pressure-volume-temperature (PVT) data manifest an anomalously accelerated non-equilibrium dynamics after a combined history of temperature and pressure cycles. This PVT data is further used to develop the KAHR structural recovery model to provide insight into the glassy dynamics. The KAHR model prediction results suggest two limitations of the model: i) the structural recovery is assumed to depend on the instantaneous liquid state, and ii) the same kinetics are assumed for the temperature and pressure perturbations. This work extends novel experiments and modeling of the non-equilibrium glassy dynamics and facilitates the development of the structural recovery theories to capture the nature of glassy relaxation for complicated temperature and pressure histories.

Embargo status: Restricted until 06/2022. To request the author grant access, click on the PDF link to the left.



Polystyrene, Pharmaceutical, Glass Transition, Structural Recovery, Configurational Entropy, Kahr Model, Activity Coefficient Model