(6fb) Engineering the Flow Properties of Colloidal Materials

Colloids are micron-sized particles that exhibit Brownian motion when suspended in a dispersed phase. Attractive and repulsive interactions can be induced between these particles, leading to phenomena such as crystallization, phase separation, and glass transition. These colloids can assemble into a broad range of structures that can be tuned for industrial and technological applications. Consequently, there has been a concerted effort to understand the microscopic contribution of particle-particle interactions to the overall structure and dynamics of a system, which ultimately leads to the ability to control material properties. How does one generate, for example, a load-bearing gel structure out of oil droplets or polymeric colloids that can support large yield stresses? What happens when roughness and shape anisotropies are introduced into the system? To address these questions, I generate a scaling law for model colloidal gels in which their non-linear flow properties can be predicted from microstructure. Measurements of the mechanics of composite hydrogels with controlled pore structures are discussed in the context of stress-bearing backbones. Experiments with dense suspensions of rough colloids (often found in consumer applications) demonstrate that the surface roughness reduces rotational freedom and is key to shear thickening and jamming in colloidal suspensions. Given the large interest in assembling targeted structures by tuning particle shape, I also present experiments and simulations that explain the unusual ability of shape-anisotropic particles to rapidly adopt certain kinds of orientational order when assembled in attraction-driven systems. By connecting the underlying physics behind the phenomenon of self-assembly and rheology, I plan to find new possibilities of designing soft materials in which the local microstructure can be modified and improved.