Johari-Goldstein Or Primitive Relaxation: Terminator Of Caged Dynamics And Precursor Of α-Relaxation

Abstract

Advance in understanding glass transition dynamics is made by identifying (1) the “universal” Johari‐Goldstein (JG) relaxation with the primitive relaxation of the coupling model and (2) the nearly constant loss (NCL) as the short time caged dynamics, all with support from experimental data. Dynamics proceeds with time in the order of vibration (boson peak), caged motions (NCL), primitive or JG relaxation, and finally the fully cooperative α‐relaxation. The primitive or JG relaxation plays two pivotal roles, the terminator of the caged dynamics (NCL) and the precursor of the α‐relaxation. The dependence of molecular mobility on thermodynamic variables such as volume and entropy enters already at early times in caged dynamics (NCL) and primitive or JG relaxation, as borne out by experimental data, and is magnified in the α‐relaxation by many‐molecule heterogeneous dynamics caused by intermolecular coupling.