Contributions to the study of the capillarity of thin liquid films

: analysis of measurements of dry spot nucleation and the use of diffuse interface theory for contact line dynamics

Abstract

The stability of thin liquid films on partially wetting substrates is of great technological importance. Attraction of the liquid by the substrate tends to destabilize the film forming dry spots. The surface tension retards this by stretching the surface of the liquid. Viscosity also determines the dynamical time scale for the nucleation (formation) of dry spots. Our work is part of an ongoing research at the MTP group of the TUE. The project comprises two parts.First part We analyze experimental data of dry spot nucleation in Triethelyne Glycol films of 30 nm to 300 nm thick on a Polycarbonate substrate. On the basis of the absence of hexagonal patterns in dry spots and the time scale deduced from a lubrication approximation of the flow we argue that strong perturbations other than ubiquitous thermal fluctuations cause dry spot nucleation in the analyzed experiments. We investigate whether substrate topography causes very fast dry spot nucleation in this experiment. Second part After the formation of small dry spots droplets are formed. In this process and other movements of droplets the dynamics of the contact line between air/liquid/substrate is crucial. A sharp interface approximation combined with the standard no-slip boundary condition used in continuum theory cannot describe contact line dynamics. A model assuming a diffuse interface was considered. In particular we propose appropriate boundary conditions at the wall for such a model.

Date of Award	30 Jun 2014
Original language	English
Supervisor	Anton A. Darhuber (Supervisor 1)