UC Santa Barbara

Granular materials are collections of discrete, macroscopic solid particles that interact primarily through dissipative contact forces. In industrial processing—ranging from pharmaceutical wet granulation to the handling of construction materials and food powders—these systems are rarely dry. Instead, they are frequently mixed with liquid binders to control dust, induce agglomeration, or modify flowability. These interstitial binders are often rheologically complex fluids containing dissolved polymers, surfactants, or suspended fines, rather than simple Newtonian liquids. Similarly, in soils, complex materials such as extracellular polymeric substances (EPS) or mucilage secreted by bacteria and plants help stabilize soil. The presence of such viscoelastic additives fundamentally alters the cohesive forces between grains, thereby modifying bulk transport behavior. At the particle scale, these complex fluids bind grains together through the formation of capillary bridges. The resulting particle-scale forces are governed not only by surface tension and viscosity but also by the fluid's elasticity and extensional rheology. In Chapter 1, we discuss the prevalence of non-Newtonian binders in industrial applications and the necessity of understanding particle-polymer interactions. In Chapters 2 and 3, we present investigations on the fundamental capillary flows of polymer solutions in droplet and bubble pinch-off configurations. In Chapters 4 and 5, we detail the development of a custom apparatus and the subsequent quantification of the axial forces arising from viscoelastic liquid bridges. Finally, in Chapter 6, we investigate the bulk flow of cohesive particulate materials, bridging the gap between microscale force measurements and macroscopic granular dynamics.