Séminaires

Pendant drops on the underside of wet surfaces : growth, motion and solidification

Pendant drops spontaneously appear on the underside of wet surfaces through the Rayleigh-Taylor instability. Due to their detrimental effect on coatings and their tendency to drip, several strategies have been developed to avoid their formation and rationalized with linear stability analysis. I will first briefly show how the Rayleigh-Taylor instability can be harnessed to make patterned elastic surfaces with a tunable spacing [1] and aspect ratio [2]. However, having a fine control over the drops in the non-linear regime of the instability is hard. They are connected to a thin film with which they continuously exchange liquid. They thus have no contact line and move around easily which disrupt the pattern. I investigate these drops dynamic experimentally, numerically and theoretically with a model system that consider a single pendant drop surrounded by a uniform thin film. I will show that under smooth surfaces, a transition from growth to decay occurs as the substrate inclination angle is increased by a few degrees [3]. I will then consider uneven surfaces, and show that the underlying topography can control the drop motion via gravito-capillary pinning-like forces [4].

[1] Marthelot, J., Strong, E. F., Reis, P. M., & Brun, P. T. (2018). Designing soft materials with interfacial instabilities in liquid films. Nature communications, 9(1), 4477.
[2] Jambon-Puillet, E., Piéchaud, M. R., & Brun, P. T. (2021). Elastic amplification of the Rayleigh–Taylor instability in solidifying melts. Proceedings of the National Academy of Sciences, 118(10), e2020701118.

[3] Jambon-Puillet, E., Ledda, P. G., Gallaire, F., & Brun, P. T. (2021). Drops on the underside of a slightly inclined wet substrate move too fast to grow. Physical review letters, 127(4), 044503.

[4] Jambon-Puillet, E. (2024). Gravito-capillary pinning of pendant droplets under wet uneven surfaces. arXiv, 2403.17584.