(142cr) Effect of Strain, Shape, and Surface Roughness On the Rheology of Colloidal Gels

Rigid, load-bearing structures have long been known as critical factors in influencing the shearing and bending properties of granular materials and fiber networks. Recently, our exploration of isostaticity in colloidal gels showed that microstructural rigidity plays an important role in their nonlinear elastic rheology. Here, we synthesize spherical and spheroidal poly(methy methacrylate) colloids with different degrees of surface roughness and incorporate depletion attractions to create weak colloidal gels. We impose simple shear flows of various strains on the gels and use a confocal laser scanning microscope to characterize the 3D structural change after deformation. This is done with a UV light-activated photopolymer, which allows particle configurations to be locked in place rapidly (< 0.6 s) after yielding. Concurrent non-linear oscillatory and stress relaxation measurements are used to determine the effect of roughness and shape on the nonlinear elasticity of the gels. In particular, surface roughness offers a potentially powerful tool for refining and controlling the rheology of colloidal gels with attractive pair potentials.