ABSTRACT
When an amorphous material in the liquid state is cooled, a temperature is reached in the vicinity of which a transition from the liquid state to the
glassy state occurs. The glassy state may also be formed if a molten crystal line material is cooled at a heating rate high enough that the development of crystalline order is prevented. Low molecular weight organic substances, inorganic salts and oxides, polymers, etc. can develop the glassy state. As Eq. (6.33) indicates, the mean relaxation time of a liquid is given by (t) = rj0/g, where r|0 and are, respectively, the viscosity and the steady-state compliance. The viscosity undergoes an anomalous increase with decreasing temperature as the temperature of the liquid comes closer to Tg, so the value of <x) becomes larger than the time scale of any available experiment. In this situation, the system falls out of equilibrium and the glassy state is formed.
