Glasses and Aging, A Statistical Mechanics Perspective on

Glossary

We start with a few concise definitions of the most important concepts discussed in this entry.

Glass transition :

For molecular liquids, the glass transition denotes a crossover from a viscous liquid to an amorphous solid. Experimentally, the crossover takes place at the glass temperature, T_g, conventionally defined as the temperature where the liquid’s viscosity reaches the arbitrary value of 10¹² Pa.s. The glass transition more generally applies to many different condensed matter systems where a crossover or, less frequently, a true phase transition takes place between an ergodic phase and a frozen, amorphous glassy phase.

Aging :

In the glass phase, disordered materials are characterized by relaxation times that exceed common observation timescales, so that a material quenched in its glass phase never reaches equilibrium (neither a metastable equilibrium). It exhibits instead an aging behavior during which its physical properties keep evolving with time.

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