Rheological hysteresis in soft glassy materials

TL;DR

This study investigates rheological hysteresis in soft glassy materials, revealing a universal timescale that governs flow behavior and hysteresis magnitude, linked to inhomogeneous flow phenomena like shear bands.

Contribution

The paper introduces two observables to quantify rheological hysteresis and demonstrates a universal timescale that varies with material complexity, unifying flow behavior in soft glassy materials.

Findings

Hysteresis observables peak at a material-dependent timescale.

This timescale increases from simple to complex materials.

Results support a universal, timescale-based framework for soft glassy rheology.

Abstract

The nonlinear rheology of a soft glassy material is captured by its constitutive relation, shear stress vs shear rate, which is most generally obtained by sweeping up or down the shear rate over a finite temporal window. For a huge amount of complex fluids, the up and down sweeps do not superimpose and define a rheological hysteresis loop. By means of extensive rheometry coupled to time-resolved velocimetry, we unravel the local scenario involved in rheological hysteresis for various types of well-studied soft materials. We introduce two observables that quantify the hysteresis in macroscopic rheology and local velocimetry respectively, as a function of the sweep rate \delta t^{-1}. Strikingly, both observables present a robust maximum with \delta t, which defines a single material-dependent timescale that grows continuously from vanishingly small values in simple yield stress fluids to large values for strongly time-dependent materials. In line with recent theoretical arguments, these experimental results hint at a universal timescale-based framework for soft glassy materials, where inhomogeneous flows characterized by shear bands and/or pluglike flow play a central role.