Deformation and relaxation of viscous thin films under bouncing drops. (4th June 2021)

• Record Type: Journal Article
• Authors: Lakshman, Srinath; Tewes, Walter; Harth, Kirsten; Snoeijer, Jacco H.; Lohse, Detlef
• Is Part Of: Journal of fluid mechanics. Volume 920(2021)
• Publication Date: 2021-06-04
• Subjects: drops, -- thin films, -- lubrication theory; Fluid mechanics -- Periodicals; 532.005
• DOI: 10.1017/jfm.2021.378
• Languages: English
• ISSNs: 0022-1120

Abstract

Abstract: Abstract : Thin, viscous liquid films subjected to impact events can deform. Here we investigate free-surface oil-film deformations that arise owing to the build up of air under the impacting and rebouncing of water drops. Using digital holographic microscopy, we measure the three-dimensional surface topography of the deformed film immediately after the drop rebound, with a resolution down to 20 nm. We first discuss how the film is initially deformed during impact, as a function of film thickness, film viscosity and drop impact speed. Subsequently, we describe the slow relaxation process of the deformed film after the rebound. Scaling laws for the broadening of the width and the decay of the amplitude of the perturbations are obtained experimentally and found to be in excellent agreement with the results from a lubrication analysis. We finally arrive at a detailed spatio–temporal description of the oil-film deformations that arise during the impact and rebouncing of water drops.