Power-law creep and residual stresses in a carbopol microgel

TL;DR

This study investigates how a carbopol microgel exhibits power-law creep and residual stresses under sub-yield shear stresses, revealing complex behaviors influenced by residual stresses and gel concentration.

Contribution

It demonstrates the power-law creep behavior in carbopol microgels and explores the effects of residual stresses and gel concentration on creep dynamics.

Findings

Power-law creep with exponent ~0.39 observed below yield stress.

Residual stresses influence anomalous creep behavior.

Creep behavior depends on gel concentration and aging effects.

Abstract

We report on the interplay between creep and residual stresses in a carbopol microgel. When a constant shear stress $\sigma$ is applied below the yield stress $\sigma_\text{y}$, the strain is shown to increase as a power law of time, $\gamma(t)=\gamma_0 + (t/\tau)^\alpha$, with an exponent $\alpha=0.39\pm 0.04$ that is strongly reminiscent of Andrade creep in hard solids. For applied shear stresses lower than some typical value $\sigma_\text{c}\simeq 0.2 \sigma_\text{y}$, the microgel experiences a more complex, anomalous creep behaviour, characterized by an initial decrease of the strain, that we attribute to the existence of residual stresses of the order of $\sigma_\text{c}$ that persist after a rest time under a zero shear rate following preshear. The influence of gel concentration on creep and residual stresses are investigated as well as possible aging effects. We discuss our results in light of previous works on colloidal glasses and other soft glassy systems.