New scaling paradigm for dynamics in glass-forming systems

Abstract

The lack of ultimate scaling relations for previtreous changes of the primary relaxation time or viscosity in glass-forming systems constitutes the grand fundamental challenge, also hindering the development of relevant material engineering applications. The report links the problem to the location of the previtreous domain remote from a hypothetical singularity. As the solution, the linearized, distortions-sensitive analysis is proposed. It is developed for scaling-relations linked to basic glass transition models: free volume, entropic, critical-like, avoided criticality, and kinetically constrained approaches. For all model scaling relations their alternative formulations based on fragility, the semi-universal metric of dynamics, are presented. The distortions-sensitive analysis is supplemented by the alternative approach based on the activation energy index showing its relative changes on cooling in the previtreous region. The search for the coherent description of the previtreous dynamics in the homologous series of polyols, from glycerol to sorbitol, is used to present in practice and validate the application of the distortions sensitive analysis. Only two scaling equation, MYEGA and the recent 'activation and critical' (AC), passed such exam. They also revealed a limited reliability of the Stickel operator' analysis for detecting the dynamic crossover. The report constitutes the unique tool-guide for applications, and a checkpoint analysis of the glass transition models. The discussion focuses on the temperature path on cooling but the extension for the still hardly discussed pressure path is also discussed.