Expérimental et théorique
Coatings of liquids on surfaces such as glass are commonly used in manufacturing processes. The stability and homogeneity of these liquid films is of course crucial to these applications. In the case of silicone oils coating glass, a rough estimate of the long-range interactions such as Van der Waals’ shows that such films should bear a uniform thickness at equilibrium: repulsive interactions should tend to a flat thick film. However, in practical situation, initially heterogeneous films never get uniform in a timely manner. As examples, defects on glass substrates lead to thickness heterogeneities that grow over time rather than heal (Figure, left). When starting from a collection of droplets sprayed onto a flat substrate (shown as dark blue disks in Fig/right), a nanometer-thick film first spreads around the droplets (yellow and cyan), and delays the spreading and coalescence of the droplets. The internship aims at gaining insights into the behavior of silicone oil on glass and to elucidate the mechanisms underlying the time evolution of such coatings. To do so, model systems will be used (plane glass or silicon wafers, well-characterized silicone oils), and experimental set-ups will be developed, in order to measure and model the time variation of silicone oil coatings at all scales.