Short and long time drop dynamics on lubricated substrates

¹ School of Engineering and Applied Sciences, Harvard University - Cambridge, MA, USA
² Department of Mechanics, Linné Flow Center, Royal Institute of Technology - Stockholm, Sweden
³ Department of Bio and Brain Engineering, Korea Advanced Institute of Science and Technology Daejeon, South Korea
⁴ Department of Mechanical and Aerospace Engineering, Princeton University - Princeton, NJ, USA

^(a) carlson@seas.harvard.edu (corresponding author)
^(b) hastone@princeton.edu (corresponding author)

Received: 21 September 2013
Accepted: 7 November 2013

Abstract

Liquid infiltrated solids have been proposed as functional solvent-phobic surfaces for handling single and multiphase flows. Implementation of such surfaces alters the interfacial transport phenomenon as compared to a dry substrate. To better understand the interface characteristics in such systems we study experimentally the dynamics of a pendant water drop in air that contacts a substrate coated by thin oil films. At short times the water drop is deformed by the oil that spreads onto the water-air interface, and the dynamics are characterized by inertial and viscous regimes. At late times, the the oil film under the drop relaxes either to a stable thin film or ruptures. In the thin film rupture regime, we measure the waiting time for the rupture as a function of the drop equilibrium contact angle on a dry substrate and the initial film height. The waiting time is rationalized by lubrication theory, which indicates that long-range intermolecular forces destabilize the oil-water interface and is the primary mechanism for the film drainage.