Rheology of Colloid Gels with Depletion and Bridging Attractions

Polymers are often added to suspensions as viscosity modifiers or stabilizers, but they can induce attractive interactions between particles that alter the suspension phase behavior and, in turn, the rheology. These attractions may be depletion attractions or bridging attractions, depending on whether the polymers adsorb on the surface of the particles. Here, we developed a model attractive colloidal suspension with depletion and bridging attractions. Co-polymer particles of 2,2,2-trifluoroethyl methacrylate and tert-butyl methacrylate were suspended in a refractive index- and density-matched mixture of glycerol and water. To these suspensions, we added poly(acrylamide) or poly(acrylic acid) to induce depletion or bridging attractions, respectively. The rheology was measured and analyzed for each set of samples with increasing concentration of polymer, corresponding to stronger attraction strengths. Significantly different rheology resulted by simply changing the polymer additive in these suspensions, suggesting that processability of suspensions may be tuned by changing the type and interactions of polymer additives in formulations.