Water film squeezed between oil and solid: drainage towards stabilization by disjoining pressure

Abstract

The spontaneous drainage of aqueous solutions of salt squeezed between an oil drop and a glass surface is studied experimentally. The thickness profile of the film is measured in space and time by reflection interference microscopy. As the film thins down, three regimes are identified: a capillary dominated regime, a mixed capillary and disjoining pressure regime, and a disjoining pressure dominated regime. These regimes are modeled within the lubrication approximation, and the role of the disjoining pressure is precisely investigated in the limit of thicknesses smaller than the range of electrostatic interactions. We derive simple analytical laws describing the drainage dynamics, thus providing tools to uncouple the effect of the film geometry from the effects of the disjoining or capillary pressures.

Self-Similar Relaxation of Confined Microfluidic Droplets

“…It is therein shown to be dominantly occupied by the inner phase and is equivalent to the best measurement we can make of the channel deformation volume at t = t off . The experimental verification of this volume conservation allows us to conclude that: i) the inner phase flows more easily than the outer phase despite the larger viscosity of the former, consistently with related experiments, theoretical and numerical works [6,22,25,26]; ii) the PDMS underlayer is fully relaxed after this initial stage; and consequently iii) thermal inertia is negligible. The observation that the inner phase flows to complete the short-time relaxation suggests furthermore that the later dynamics is in turn limited by the outer phase.…”

“…The relaxation dynamics of liquid interfaces towards equilibrium induced by surface tension has been studied for many decades [1][2][3][4][5][6][7]. The gradient of capillary pressure determined by the interface curvature along the deformed surface generates a flow, which in turn is limited by viscous stresses.…”

“…In the context of droplet relaxation, experimental, theoretical and numerical studies considered a droplet immersed in an infinite bath [2,15,16] or confined by two parallel walls [12,17,18]. As such, droplet relaxation could be reduced to one of its planes of invariance [2,6,12]. Such simplifications aid in the analytic resolution of dynamical relaxation problems.…”

Laplace pressure based disjoining pressure isotherm in non symmetric conditions

“…1,16 Consequently, fluid-liquid-solid configurations are commonly studied using a bubble or droplet mechanically pressed over a wetting film deposited on a substrate. [17][18][19][20] The maximum disjoining pressure range experimentally achieved with this technique lies below 500 Pa. A major limitation of those methods is the drainage time one has to wait between two measurement points as it can last several hours.…”

Hyperspectral imaging for dynamic thin film interferometry

“…This approach is quite robust, however it is quite slow and suffers from human subjectivity. Another common approach utilizes fringe counting from a known absolute reference thickness in the film [25][26][27] . This approach is quite fast but is not robust and requires assumptions on the spatial structure of the film.…”