Beta relaxation in the shear mechanics of equilibrium viscous liquids: Phenomenology and network modeling of the alpha-beta merging region

TL;DR

This paper explores the beta relaxation process in shear mechanics of glass-forming liquids, comparing it to dielectric behavior, and proposes a viscoelastic model that fits experimental data for Polyisobutylene 680.

Contribution

It introduces a physically motivated additive shear compliance model for alpha and beta relaxations and demonstrates its applicability to experimental data.

Findings

The model captures the merging of alpha and beta relaxation regions.

Additivity in shear compliance is essential for physically relevant models.

The proposed model fits experimental data for Polyisobutylene 680.

Abstract

The phenomenology of the beta relaxation process in the shear-mechanical response of glass-forming liquids is summarized and compared to that of the dielectric beta process. Furthermore, we discuss how to model the observations by means of standard viscoelastic modeling elements. Necessary physical requirements to such a model are outlined, and it is argued that physically relevant models must be additive in the shear compliance of the alpha and beta parts. A model based on these considerations is proposed and fitted to data for Polyisobutylene 680.