“Our results are new and present a challenge to theoretical models that attempt to explain the glass transition.”

The glass transition is considered one of the most important unsolved problems in the study of condensed matter physics (CMP). Our paper is highly cited because it presents a novel approach to this phenomenon, which quantifies the roles of temperature and volume. The interrelation of these variables is described in terms of a single parameter, which is a material constant. Moreover, this parameter enables dynamic properties measured over a broad range of thermodynamic conditions to be superposed onto a single master curve.

Our results are new and present a challenge to theoretical models that attempt to explain the glass transition. They also provide an empirically useful methodology that allows the behavior of dynamical properties such as viscosity and relaxation time to be predicted for any given condition of temperature, density, and pressure. Examples of this utility include estimating the viscosity of a polymer melt when injected into a mold at high pressure and high temperature, or the viscosity of magma at the extreme conditions found below the Earth’s surface.

A liquid or polymer sufficiently cooled or compressed will transform into a solid (a glass) while retaining its disordered microscopic structure. The physics underlying this transition are poorly understood. Models generally interpret the transition in terms of either a jamming of molecular motions due to reduction in the volume available for the molecules to rearrange, or a slowing down of the molecular motions due to a decrease in the energy available to each molecule. However, neither of these descriptions is satisfactory. Our scaling shows how these two effects can be deconvoluted to give a unified description in terms of both temperature and volume.

We have been studying the glass transition for over a decade and in the last five years began to emphasize measurements taken under high-pressure conditions. The resulting experimental data revealed new physics, which have allowed a different interpretation of the behavior of glass-forming liquids and polymers. As our experimental capabilities evolved, we have been able to characterize diverse materials with various properties, thus providing a more complete picture of the glass-transition phenomenon. The applicability of our thermodynamical scaling (now verified by several other groups) will certainly help bring resolution to this important area of CMP.