Impact and spreading dynamics of fiber suspension droplets on a solid surface

The impact and spreading of drops of particulate suspensions on solid surfaces is relevant in various industrial applications such as inkjet printing or spray coating tablets in the pharmaceutical industry. The capillary dynamics of elongated particles, such as fibers, are also important in extrusion-based additive manufacturing when bioprinting cells or fiber suspensions used for fiber composites. However, the role and dynamics of fiber suspensions during capillary flows remain elusive. In particular, fibers can influence the impact of a droplet, from its spreading to splashing. In this study, we experimentally investigate the impact of droplets of fiber suspensions on a hydrophilic surface. We report the evolution of the spreading dynamics, thresholds for splashing, film thickness, and fiber orientation as a function of the radial distance for fiber suspensions of varying mass fraction and aspect ratios. Our experiments show a substantial modification in the spreading dynamics of the drop due to the presence of fibers.