‘Intra-cluster rearrangement' model for the α-process in supercooled liquids, as opposed to ‘cooperative rearrangement of whole molecules within a cluster'

A new model for the α-relaxation process in supercooled liquids and glasses is proposed which distinguishes between a structurally correlated region (cluster) of molecules and a unit of molecules for rather independent, correlated rearrangement motion. The essential aspects of the model are that the α-process is due to rearrangement of one or a few molecules within the cluster, while essentially the same motion in the space between the clusters is responsible for the β-process. The model leads to the following expectations: (i) absence of divergent behavior of α-relaxation times at non-zero temperature (e.g., Kauzmann temperature), (ii) close agreement between the glass transition temperatures, T_g, for the α-relaxation in liquid and crystalline phases of the same composition and (iii) possibility of crystal nucleation proceeding much below the T_g, and evidence for the latter two is presented.