(498a) Tuning the Yield Stress in Suspensions of Soft Colloids

The yield stress is an important physical parameter that controls how a material flows during processing and retains its shape once delivered. Control over this parameter dictates the performance of complex fluids in applications ranging from 3D printing to therapeutics to consumer products. Here, we investigate the behavior of two different classes of soft colloids – emulsion droplets and porous microcapsules – and demonstrate control over the yield transition through the addition of polymers. We form microcapsules through the complexation of cellulose nanofibrils and oleylamine. During preparation, poly(acrylic acid) is added to the internal phase of the capsules, which leads to the emergence of a yield stress that increases with increasing polymer concentration. In the emulsion system, we stabilize cyclohexane droplets in water using a triblock copolymer that fractionally bridges between droplets to generate an elastic network. We control the resulting yield stress in these polymer-linked emulsions through the polymer concentration, emulsion volume fraction, and temperature. With these findings, we demonstrate methods to introduce and control the yield transition in suspensions of soft colloids.