My current research subjects are focused on the understanding of the out-of-equilibrium dynamics of flows where surface tension forces play a dominant role. This happens when one of the typical scale of the problem is between 1 micron and a few mm. Current applications are mostly related to the handling of small droplets, that are more and more utilized in discrete microfluidics. Typical situations are the displacement of sessile droplets against capillary retention forces acting at the contact-line. With surface acoustic waves (SAW), it is possible to induce both the inner mixing and displacement of the drop.

Another reminiscent issue, is to understand what governs the forced imbibition in textured non-wetting (superhydrophobic) surfaces. We use both drop-impact and electrowetting to induce impalement within such surfaces.

More generally, the interaction of a sessile drop with its substrate, and particularly the case of dynamical wetting, still offers hot debates (see these two recent reviews on the subject here and here).



As side-projects, I have investigated the famous 'Edgerton's crown' problem, ie the fingering pattern following the impact of a drop on a thin fluid layer. I have also been studying the instabilities (surface deformations) and rupture of a liquid curtain subjected to local perturbations.


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With: Farzam Zoueshtiagh, Alain Merlen (team FILMS - IEMN)
Florian Lapierre, Vincent Thomy (team BIOMEMS - IEMN)
Nhung Phuong Nguyen, Yannick Coffinier, Rabah Boukheroub & Ralf Blossey (Institut de Recherche Interdisciplinaire – IRI)




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With: Farzam Zoueshtiagh, Michael Baudoin, Olivier Bou Matar & Alain Merlen (team FILMS – IEMN)







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WithJacco H. Snoeijer (Physics of Fluids Group - University of Twente, The Netherlands). and Jens Eggers (University of Bristol, UK)



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With: Michael Baudoin (team FILMS - IEMN)



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With:  Stephane Dorbolo (GRASP - University of Liege, Belgium)



With:  Robert Deegan (University of Michigan, USA) and Jens Eggers (University of Bristol, UK)


Snapshots taken at between 0.8 and 1.5 ms after impact. A drop of silicon oil targeting a thin layer of fluid at V between 3 m/s and 3.5 m/s. An annular sheet develops after impact, surrounded by a liquid 'rim'. The destabilization of the rim (initially smooth and unperturbed) shows a fingering pattern with a well-defined wavelength.


     

 

At higher Reynolds number (experiments carried out with water), a noisy structure of tiny jets appears at the early stage and the subsequent wavelength of the fingering structure is less regular.

                                         

                t ≈ 0.15 ms                                                          t ≈ 2 ms                                                              t ≈ 4 ms

 



Snapshots (t=0, 4.76, 9.05 and 13.33 ms) of a 5 ml climbing drop of glycerin on an inclined plate (inclination 45 degrees) shaken at 60 Hz.


Here are movies to download:


images\rocking_highspeed.avi : a 2100 fr/sec. movie showing the rocking motion of a climbing drop, when shaken at 60 Hz.

images\movie_20hz.avi : a 20 fr/sec. movie, showing a climbing drop. Snapshots are taken every 3 periods, at the same phase, then enabling to see the global motion.

images\pearling-1.avi : a 2100 fr/sec movie of an horizontal plate shaken diagonally (an analogue of the previous situation, but suppressing gravity), showing ultimately a pearling instability at the drop's trailing end.

images\sliding_climbing-1.avi : a 100 fr/sec movie, showing both the shaking and the deformation of the drop. First, the drop slides down the incline, and once the shaking is prescribed it climbs up!



     From n=2 to n=13: Various spatial modes appearing when a drop is put on a shaken hydrophobic substrate (frequency ranges from 15 to 200 Hz).

    A similar spontaneous break of axisymmetry is observed with Leidenfrost drops (Propanol, substrate temperature between 200 and 220 C).






Previous research activities :

 - PhD Thesis: STRUCTURES AND NON-LINEAR DYNAMICS OF FALLING LIQUIDS (At PMMH Laboratory, Paris)

A gallery of pictures ...

 Photo Photo Photo Photo Photo Photo

Thesis available online.

(In french only).

 - STATIC GRANULAR PACKINGS : Mechanical response and the influence of  the packing preparation (At the former LMDH laboratory , Paris, Newly settled here) .

 

- CONTROL OF THERMOCAPILLARY  INSTABILITIES (At KTH Mekanik, Stockholm, Sweden).

 

- FORCED IMBIBITION AND DRAINAGE IN HYDROPHOBIC POROUS MEDIA (At KTH Mekanik and Faxen Laboratory, Stockholm, Sweden).