A liquid, if it does not crystallize on cooling, can undergo a “glass transition”, a falling-out-of equilibrium in terms of motion and rearrangement of its molecular constituents. The rapid increase in viscosity near the glass transition temperature, Tg, transforms the flowing liquid into a rigid solid without the long-range order characteristic of crystals.
Glassy materials are ubiquitous, we use them as building material, to make optic fiber for telecommunication, flat panels for optical display, lenses for camera and telescope, to replace small bones in our body and as host materials for encapsulation of radioactive waste and preservation of biomaterials and drugs. Organic glassy phases are polymers, and sugar candy. Finally, glasses also occur in nature as vocanic rocks and in outer space as glassy ice!
Most people realize that these are hard and solid-like at room temperature but soften and flow on heating. But few realize the commonality of phenomena in the glassy state as applied to these and other systems. The distinctive behavior of the glassy and liquid states, and of the glass transition relating them, has ramifications for processes as diverse as semiconductor, glass, plastic and food manufacturing, volcanism, the survival of bacterial spores, and the preservation of red blood cells in vitro.