  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.
