title: How microstructures affect air film dynamics prior to drop impact.
abstract: When a drop impacts a surface, a dimple can be formed due to the increased air pressure beneath the drop before it wets the surface. We employ a high-speed color interferometry technique to measure the evolution of the air layer profiles under millimeter-sized drops impacting hydrophobic micropatterned surfaces for impact velocities of typically 0.4 m s(-1). We account for the impact phenomena and show the influence of the micropillar spacing and height on the air layer profiles. A decrease in pillar spacing increases the height of the air dimple below the impacting drop. Before complete wetting, when the impacting drop only wets the top of the pillars, the air-droplet interface deforms in between the pillars. For large pillar heights the deformation is larger, but the dimple height is hardly influenced.
authors.affiliation: Physics of Fluids Group, MESA+ Institute for Nanotechnology and J. M. Burgers Centre for Fluid Dynamics, University of Twente, P.O. Box 217, 7500AE Enschede, The Netherlands. r.c.a.vanderveen@utwente.nl d.lohse@utwente.nl.
authors.forename: Roeland C A
authors.initials: RC
authors.lastname: van der Veen
authors.forename: Maurice H W
authors.initials: MH
authors.lastname: Hendrix
authors.forename: Tuan
authors.initials: T
authors.lastname: Tran
authors.forename: Chao
authors.initials: C
authors.lastname: Sun
authors.forename: Peichun Amy
authors.initials: PA
authors.lastname: Tsai
authors.forename: Detlef
authors.initials: D
authors.lastname: Lohse