Welcome to the Glass Age

198 derivatives [5]. Beyond chemical considerations, researchers work with computer or physical models comprised of hard spheres or other objects with variable interaction terms replacing chemical bonds, spin glasses evolve from magnetic disorder, and many other manifestations of glassy disorder are being explored as examples for the dynamics of complex systems. Thereby, the glass itself often provides a snapshot of the liquid from which it was obtained: while a liquid is hard to observe, once its dynamics are frozen-in, a plethora of analytical tools becomes available and can give further insight on structure-property relationships. A material driven by process technology Returning to the transition from liquid to glass, it is precisely this characteristic that constitutes the practical interest and industrial importance of glasses and vitreous materials: the temperature dependence of the viscosity of glass-forming melts and their (super-cooled) liquids. The most widespread route to create a glass is to cool down a liquid sufficiently rapidly, which leads to an increase in viscosity and, thus, a decrease in the mobility of the liquid’s (atomic) constituents. This latter effect creates a kinetic barrier against assembling into the ordered crystalline state; instead a glass transition occurs at which the structural configuration of the liquid is trapped. Cooperative translational movements are no longer possible. As a consequence, the glass is a solid, but it has the molecular structure of a liquid. The reason as to why this transition occurs within such a relatively narrow temperature window remains largely unknown. However, the simple fact of tunable viscosity (using temperature) leads to the universal processability of glass-forming melts: in principle, there is a specific viscosity range for any conceivable shaping problem: fiber can be drawn, bottles be blown, filaments or microbeads be atomized, sprayed or spun, or thin sheet and even membranes be drawn, flown or floated. The technological challenge then is the development of appropriate molding machines and process chains, for