Wave turbulence on the surface of a ferrofluid in a horizontal magnetic field

We report observations of wave turbulence on the surface of a ferrofluid submitted to a magnetic field parallel to the fluid surface. The magnetic wave turbulence shows several differences compared to the normal field case reported recently. The inertial zone of the magnetic wave turbulence regime is notably found to be strongly increased with respect to the normal field case, and to be well described by our theoretical predictions. The dispersion relation of linear waves is also measured and differs from the normal field case due to the absence of the Rosensweig instability.Comment: in press in Phys. Rev. E (2011

Droplets climbing a rotating helical fiber

A liquid droplet is placed on a rotating helical fiber. We find that the droplet may slide down, attach or climb up the fiber. We inspect experimentally the domain of existence of these three behaviors as a function of the geometrical characteristics of the fiber, its angle relatively to the horizontal, the wetting properties of the fluid and the rotating speed of the helix. A theoretical model is proposed in order to capture the boundaries of the experimental phase diagram

Wicking through a confined micropillar array

This study considers the spreading of a Newtonian and perfectly wetting liquid in a square array of cylindric micropillars confined between two plates. We show experimentally that the dynamics of the contact line follows a Washburn-like law which depends on the characteristics of the micropillar array (height, diameter and pitch). The presence of pillars can either enhanced or slow down the motion of the contact line. A theoretical model based on capillary and viscous forces has been developed in order to rationalize our observations. Finally, the impact of pillars on the volumic flow rate of liquid which is pumped in the microchannel is inspected

Single thermal plume in locally heated vertical soap films

peer reviewe

A drop of spectroscopy

peer reviewedWhen a low viscosity oil droplet is laid onto the surface ofa high viscosity oil liquid, it stays at rest for a moment before coalescence. The coalescence can be delayed and sometimes inlibited by injecting fresh air under the droplet. This can happen when the surface ofthe bath oscillates vertically. In this case the droplet basically bounces on the interface. We obsewe that the conditions for bouncing depends on the frequency, more precisely we observe resonance when the eigenfrequency of the droplet is excited. In some conditions, a droplet presents a non axi- symmetric mode of deformation. That leads to a rotation of the droplet and to a horizontal displacement

Dynamics of a grain-filled ball on a vibrating plate

peer reviewe

Antibubble dynamics : slipping or viscous interfaces ?

An antibubble is a spherical 1µm-thick air shell that is immersed in a water-surfactant mixture and drains under the action of hydrostatic pressure. A lubrication model has been built to account for the role of intrinsic surface viscosity at the shell interfaces. Solutions show a plug (resp. Poiseuille) flow for low (resp. high) surface viscosity. Comparison of antibubble lifetimes with available experimental data is in qualitative agreement. We thus believe that this work could also be relevant to other microfluidic systems involving fluid-fluid interfaces with surface-active materials