Signatures of Physical Aging and Thixotropy in Aqueous Dispersion of Carbopol

TL;DR

This study reveals physical aging and thixotropic behavior in aqueous Carbopol dispersions, demonstrating time-dependent relaxation, superposition principles, and Andrade creep, despite weak elastic modulus changes.

Contribution

It provides new insights into aging signatures and relaxation dynamics in Carbopol dispersions, highlighting superposition behaviors and stress-dependent relaxation spectra.

Findings

Creep and strain recovery depend on waiting time since shear melting.

Time waiting time superposition observed in corrected strain in effective time domain.

Relaxation time follows a power-law dependence, decreasing with stress.

Abstract

In this work, we investigate signatures of physical aging in an aqueous dispersion of Carbopol that shows yield stress and weak enhancement in elastic modulus as a function of time. We observe that the creep curves, as well as strain recovery, show a significant dependence on waiting time elapsed since shear melting. The corrected strain, which is the strain in excess of the recovered strain, has been observed to show time waiting time superposition in the effective time domain, wherein time is normalized by time-dependent relaxation time that shows a power-law dependence. The corresponding power law exponent, which is close to unity in a limit of small stresses, decreases with stress and tends to zero as stress approaches the yield stress. For a range of stresses, the material shows time stress superposition suggesting the shape of the evolving relaxation time spectrum to be independent of the time as well as the stress. This work, therefore, suggests the presence of physical aging in an aqueous dispersion of Carbopol even though the elastic modulus shows only a weak enhancement. We also discuss Andrade type of creep behavior in aqueous Carbopol dispersion.