Lubrication films

A question as simple as predicting the droplet velocity while pushed by an external fluid at fixed velocity is still not answered [2]. Understanding and thus modelizing it requires the identification of dissipation mechanisms in the droplet, in the dynamical meniscus and in the flat film.

We studied the dynamical properties of lubrication films using an interferometric method (RICM) that has been adapted to microfluidics [5]. We first showed that, in a static case, we are able to measure nanometric film thicknesses with very accurate precision and that it is set by the disjoining pressure,

especially the electrostatic part [9]. Then the film was studied when the droplets flow. At low speeds, the film thickness is set by the disjoining pressure, while at higher capilarry numbers we identified a viscous model in agreement with our experimental results [4]. For a micellar solution, we observed spinodal decomposition allowing us to recover interfacial properties (velocity, Marangoni stress).