Restructuring and aging in a capillary suspension

TL;DR

This study explores how capillary suspensions, with added immiscible fluids, age and restructure under rest and shear, revealing their unique sensitivity to deformation and differences from van der Waals dominated gels.

Contribution

It provides new insights into the aging and restructuring behavior of capillary suspensions under various shear conditions, highlighting their distinct rheological responses.

Findings

Capillary suspensions show power-law aging behavior.

They are highly sensitive to small oscillatory deformations.

High shear rates are needed to rupture the network.

Abstract

The rheological properties of capillary suspensions, suspensions with small amounts of an added immiscible fluid, are dramatically altered with the addition of the secondary fluid. We investigate a capillary suspension to determine how the network ages and restructures at rest and under applied external shear deformation. The present work uses calcium carbonate suspended in silicone oil (11 % solids) with added water as a model system. Aging of capillary suspensions and their response to applied oscillatory shear is distinctly different from particulate gels dominated by the van der Waals forces. The suspensions dominated by the capillary force are very sensitive to oscillatory flow, with the linear viscoelastic regime ending at a deformation of only 0.1 % and demonstrating power-law aging behavior. This aging persists for long times at low deformations or for shorter times with a sudden decrease in the strength at higher deformations. This aging behavior suggests that the network is able to rearrange and even rupture. This same sensitivity is not demonstrated in shear flow where very high shear rates are required to rupture the agglomerates returning the apparent viscosity of capillary suspensions to the same viscosity as for the pure vdW suspension. A transitional region is also present at intermediate water contents wherein the material response depends very strongly on the type, strength, and duration of the external forcing.