Glass-forming liquids and the glass transition: The energy landscape approach to dynamics and thermodynamics

Abstract

Most liquids, under suitable conditions, are capable of transforming into glass, which is a microscopically disordered, solid form of matter. Glass formation occurs in the laboratory because the viscosity of the liquid becomes very high, causing the liquid to fall out of equilibrium on experimental time scales. Whether a true thermodynamic transition underlies the laboratory transformation is among the questions that remains to be answered. Another major theme of research activity is directed towards understanding the microscopic mechanisms leading to the dramatic growth of viscosity of liquids at low temperatures. Significant progress has recently been made by focusing attention on quantitative aspects of the energy landscape of glass-forming liquids. An outline of the approach is presented here, along with applications of the approach to studying thermodynamic and dynamic phenomena that take place when a liquid is cooled towards the glass transition, including: (i) The onset of slow dynamics; (ii) The crossover in dynamics to a regime of 'activated dynamics'; (iii) The relationship between fragility (which quantifies the rapidity of change of dynamics as the glass transition is approached) and quantifiable
features of the energy landscape; and (iv) The relationship between the ultimate boundaries of the liquid state, the liquid-gas spinodal (at which liquid becomes thermodynamically unstable) and the glass transition line (at which liquid transforms into an amorphous solid).