Residual stresses and shear-induced overaging in boehmite gels

Abstract

Colloidal gels respond like soft solids at rest, whereas they flow like liquids under external shear. Starting from a fluidized state under an applied shear rate γp, abrupt flow cessation triggers a liquidto-solid transition during which the stress relaxes towards a so-called residual stress σres that tallies a macroscopic signature of previous shear history. Here, we report on the liquid-to-solid transition in gels of boehmite, an aluminum oxide, that shows a remarkable non-monotonic stress relaxation towards a residual stress σres( γp) characterized by a dual behavior relative to a critical value γc of the shear rate γp. Following shear at γp > γc, the gel obtained upon flow cessation is insensitive to shear history, and the residual stress is negligible. However, for γp < γc, the gel encodes some memory of the shear history, and σres increases for decreasing shear rate, directly contributing to reinforcing the gel viscoelastic properties. Moreover, we show that both σres and the gel viscoelastic properties increase logarithmically with the strain accumulated during the shear period preceding flow cessation. Such a shear-induced "overaging" phenomenon bears great potential for tuning the rheological properties of colloidal gels.

Residual stress in athermal soft disordered solids: insights from microscopic and mesoscale models

“…Future work can explore gel-like materials where more complex, i.e. nonmonotonic, stress-relaxation after shear cessation has been reported [58][59][60] and has been attributed to overaging. Furthermore, there is scope for improvement in the mesoscale modeling to become more quantitative.…”