Capillary bridging and microstructural evolution in suspensions of cube-shaped particles: The role of wettability and...

The distinct orientations of anisotropic particles offer an advantage in designing capillary suspensions with superior rheological properties compared to isotropic particles. However, this aspect remains underexplored and should be studied in greater detail. Specifically, cube-shaped particles provide six flat faces per particle for capillary bridge formation and enable diverse microstructural assemblies driven by their wettability. The side-by-side bridging can facilitate enhanced rheological properties of the capillary suspensions.

Capillary suspensions are prepared with in-situ and ex-situ surface-modified cube-shaped particles. The rheological and microstructural properties are investigated for varied preferential/partially wetting secondary fluids and particle volume fractions using a rheometer and optical microscopy, respectively.

In preferential wetting conditions, maximum yield stress is obtained due to side-by-side particle arrangements in the pendular state. These structures evolve into merged chains with ordering, and eventually into disordered bicontinuous networks as the secondary fluid amount increases. The formation of the bicontinuous network caused a slight decay in yield stress. In contrast, under partial wetting conditions, the networks exhibit local ordering that transitions to emulsions upon increasing the amount of secondary fluid, and the yield stress follows a non-monotonic trend. A comparative study reveals that cubes form significantly stronger gels than the irregular particles at equivalent volume fractions. Additionally, capillary force calculations demonstrate that, when cube particles are in contact, the Laplace forces are dominant due to their side-by-side configurations. These findings underscore the critical role of particle shape and ordering in tuning the rheological properties of capillary suspensions.