This thesis investigates several free-surface phenomena to illustrate the role of viscous stresses.
In part I (chapters 1-4), we study the impact of spherical liquid drops on non-wetting substrates. After impact on a rigid substrate, a falling liquid drop deforms and spreads, owing to the normal reaction force. Subsequently, if the substrate is non-wetting, the drop retracts and then jumps off. As we show in chapter 1, not only is the impact itself associated with a distinct peak in the temporal evolution of the normal force, but also the jump-off, which was hitherto unknown. Throughout this drop impact process, viscous dissipation enervates internal momentum. Subsequently, gravity and viscosity conspire to inhibit bouncing, which we delineate in chapter 2. Furthermore, chapter 3 investigates drops bouncing off viscous liquid films that mimic atomically smooth substrates. Then, in chapter 4, we examine the drop-on-drop impact process whereby an impacting liquid drop lifts off a lazy sessile one from a non-wetting substrate.
In part II (chapters 5-6), we focus on capillary-driven retraction of films and the bursting of free-surface bubbles. In chapter 5, we show that even when the surrounding medium interacts with the Taylor-Culick retraction of a film, the film still retracts with a constant velocity, provided that it is long enough to avoid finite film size and internal viscous effects. Lastly, in chapter 6, we reveal that the influence of viscoplasticity on the capillary-driven bursting of a bubble at a liquid-gas free-surface is twofold: (i) it manifests as an increase in effective viscosity to attenuate the capillary waves that control the bursting process, and (ii) the plasticity of the medium resists any attempts to deform its free-surface.
- bubble dynamics
- free-surface flows