UC Santa Barbara

Capillary flows of suspensions are critical in applications ranging from inkjet printing and 3D printing to the manufacturing of paints and coatings. These processes involve the interplay of capillary, viscous, inertial, and gravitational forces that govern the behavior of suspensions at microscopic scales. This thesis investigates the pinch-off dynamics of bidisperse spherical suspensions and the impact and spreading of fiber suspensions, which are relevant for optimizing droplet formation, extrusion, and deposition processes. The study on bidisperse suspensions reveal a modified pinch-off dynamics. Through our experiments, we reveal that this modified pinch-off dynamics is a result of the new length-scale introduced by the size of the particles close to break-up. In our study on drop impact of fiber suspensions, a notable result is the decrease in the size of the droplet as it spreads, due to increase in the suspension viscosity. A consequence of this is a decrease in the droplet size and modified coating properties as a function of the fiber volume fraction in the suspension.

The thesis also provides a broader framework for understanding the rheology of particulate suspensions, with a focus on both spherical and anisotropic particles. By leveraging classical models for viscosity, such as the Maron-Pierce correlation, it explores how particle shape, size distribution, and volume fraction influence suspension viscosity across different regimes. In dense systems, the maximum packing fraction becomes a limiting factor, particularly for fiber suspensions, where the geometry of the fibers plays a significant role. This work advances the understanding of suspension behavior in unbounded flow systems, such as during the extrusion of a droplet from the nozzle, offering insights that are critical for applications requiring precise control of suspension flow and deposition.