Elastohydrodynamic and capillary thin film flows at small scales

Abstract

Thin viscous films are ubiquitous in Nature and biology and they are indispensable in industrial applications through lubrication and coating. In order to utilize the potential of thin viscous films on the micro and nano scale, detailed understanding and models of the mechanisms that govern the flow dynamics is necessary. In the presented thesis, I investigate how the flow dynamics are influenced by small scale effects using mathematical and numerical modelling. More specifically, small scale flow phenomena driven by elastic bending, thermal fluctuations and surface tensions forces are studied. A main objective was to identify time and length scales on which characteristic thin film flow features such as perturbation levelling and film rupture/de-wetting occur. This has great practical implications as it can be used to improve a films stability and provide estimates of the system's total surface energy. Moreover, thermal fluctuations are demonstrated to be able to influence these time scales to a great extent. Furthermore, I investigate how wetting droplets on conical structures can self-propell due to a mismatch in the droplets front and trailing contact angle. The latter has significant potential to create passively coated structures and to enhance water transport in fog nets.