Impingement of a compound drop on a substrate and emulsification of silicone oil in an eye-on-a-chip

Abstract

Wetting and dewetting are commonly observed processes at solid-liquid interface. In this thesis, we mainly focus on the two specific phenomena at the solid-liquid interface: impact of a compound drop on a solid substrate and adhesion of silicone oil on a cell-lined surface. By studying these two phenomena, we extend the knowledge of understanding of compound droplet impact and reveal a novel mechanism of silicone oil emulsification in ophthalmology. We study the behavior of a compound drop on a partially wetting surface in Chapter 2. The oil-water compound drop is generated by a coaxial needle at millimeter scale. A compound drop tends to spread slower and rebound higher, which is compared with impact of a single-component drop both qualitatively and quantitatively. The relationship between the maximum spreading diameter of compound drops and Weber Number is investigated. A single-component drop or a compound drop with a small core-shell ratio (<0.7) cannot rebound on a wetting surface when falling height is at the range of 0-20 cm (Weber number < 150). While a compound drop with a large core-shell ratio (>0.75) tend to rebound with a small impinging velocity. The spreading and rebounding of a compound drop is not significantly different for different partial wetting surfaces. We study the emulsification of silicone oil with high-molecule-weight additives in an eye-on-a-chip and in a cell-lined device in Chapter 3. To test the resistance against emulsification, silicone oil is tested in an eye-on-a-chip device with simulated saccadic eye motion for four days. The number of emulsified droplets in high-molecule-weight silicone oil is smaller than that in conventional silicone oil. We find the adhesion of silicone oil is a possible reason of emulsification, and the extensional viscosity increase in high-molecular weight silicone oil increase the resistance against emulsification. Adhesion of silicone oil is demonstrated in a cell-lined microchannel.