Shear stresses of colloidal dispersions at the glass transition in equilibrium and in flow

TL;DR

This study explores the relationship between equilibrium stress fluctuations and shear stresses in dense colloidal dispersions near the glass transition, combining experiments with theoretical models to understand non-linear rheology.

Contribution

It introduces experimental data on shear stresses in colloidal glasses and compares them with mode coupling theory, revealing insights into non-linear rheology at the glass transition.

Findings

Theoretical models semi-quantitatively fit experimental data in fluid and glassy states.

A dissipative mechanism in glassy states is identified but not yet fully explained.

Connection between non-linear rheology and glass transition is clarified.

Abstract

We consider a model dense colloidal dispersion at the glass transition, and investigate the connection between equilibrium stress fluctuations, seen in linear shear moduli, and the shear stresses under strong flow conditions far from equilibrium, viz. flow curves for finite shear rates. To this purpose thermosensitive core-shell particles consisting of a polystyrene core and a crosslinked poly(N-isopropylacrylamide)(PNIPAM) shell were synthesized. Data over an extended range in shear rates and frequencies are compared to theoretical results from integrations through transients and mode coupling approaches. The connection between non-linear rheology and glass transition is clarified. While the theoretical models semi-quantitatively fit the data taken in fluid states and the predominant elastic response of glass, a yet unaccounted dissipative mechanism is identified in glassy states.