Dynamic structure factor near the glass transition : specific features

The dynamic structure factor in the supercooled liquid state just above the glass transition temperature reveals a number of characteristic universal features in the so-called "fragile" class of glassy systems. A theory independent, unbiased analysis shows that, compared to the behaviour expected in the ordinary liquid state, one can observe: (a) a two-step pattern in the time relaxation of the liquid structure factor, the slower of these steps scaling with the bulk viscosity, (b) a relatively small, oscillatory wavenumber dependence of the relaxation dynamics, and (c) approximate master functions of unconventional shapes for both relaxation steps. These qualitative features are in agreement with predictions of recent mode coupling theories and, in addition, the quantitative behaviour is also compatible with the theoretically predicted scaling properties.