Drops and jets dynamics: vibrations of drops, jet bouncing on hydrophobic and superhydrophobic surfaces.
With F. Celestini, R. Kofman (LPMC, Nice, France).
  We have studied the combined effects of vertical and horizontal vibrations which can lead to controlled displacement of droplets.

We focused on the motion of a drop lying on a vibrated plate simultaneously submitted to horizontal and vertical harmonic vibrations. The two driving vibrations are adjusted to the same frequency, but according to their relative amplitude and phase difference ΔΦ the drop experiences a controlled directed motion with a tunable velocity. We present a simple model enlightening the underlying mechanism leading to a net motion of a drop. The particular case ΔΦ = π corresponds to the climbing of a drop on a vertically vibrated inclined substrate as recently observed by Brunet et al. Our study gives insights in the fundamental study of wetting dynamics and offers new possibilities of controlled motion in droplet microfluidics application.
shaken drops

In this movie (HQ: 24 Mo) (LQ: 10 Mo) we show how drops can be displaced on a surface using combined vibrations.

With F. Celestini, R. Kofman, M. Pellegrin (LPMC, Nice, France)
   When a water jet impinges upon a solid surface it produces a so called hydraulic jump that everyone can observe in the sink of its kitchen. It is characterized by a thin liquid sheet bounded by a circular rise of the surface due to capillary and gravitational forces. In this phenomenon, the impact induces a geometrical transition, from the cylindrical one of the jet to the bi-dimensional one of the film. A true jet rebound on a solid surface, for which the cylindrical geometry is preserved, has never been yet observed. We have experimentally demonstrated that a water jet can impact a solid surface without being destabilized. Depending on the incident angle of the impinging jet, its velocity and the degree of hydrophobicity of the substrate, the jet can: i) bounce on the surface with a fixed reflected angle, ii) land on it and give rise to a supported jet or iii) be destabilized, emitting drops. Capillary forces are predominant at the sub-millimetric jet scale considered in this work, along with the hydrophobic nature of the substrat to explain why such capillary hydraulic jump gives rise to this unexpected jet rebound phenomenon. 
Jet bouncing

  • Vertical vibration of drops: contact angle hysteresis and instabilities
With A. Buguin and F. Brochard-Wyart (Physico-Chimie Curie, Paris, France)
  We have studied the effect of vertical vibrations of sessile drops and puddle (frequency fe). Above a first threshold in amplitude, we observe the depinning of the line and the radius of the puddle starts to oscillates. Above a second threshold, we observe an instability of the contour at frequency fe/2, parametrically excited by the variations of the drop radius. See my Ph.D thesis for more details.

Vertical modes of vibrations
Triplons modes of puddles

  • Inertial dewetting
With A. Buguin and F. Brochard-Wyart (Physico-Chimie Curie, Paris, France)
   We have studied the fast dewetting of a water film floating on a non miscible liquid substrate, denser and non miscible. We have measured the dewetting velocity V versus the film thickness e. When V is larger than the velocity of surface waves, we observe a cascade of shocks propagating ahead or behind the rim collecting the water. See my Ph.D thesis for more details.

Surface waves generated by dewetting