If liquids, polymers, bio-materials, metals and molten salts can avoid crystallization during cooling or compression, they freeze into a microscopically disordered solid-like state, a glass. On approaching the glass transition, particles become trapped in transient cagesin which they rattle on picosecond timescalesformed by their nearest neighbours; the particles spend increasing amounts of time in their cages as the average escape time, or structural relaxation time α, increases from a few ...
