MAIN RESEARCH INTERESTS of the GROUP

Matière molle, Instabilités et transitions de phases

(soft matter, instabilities and phase transitions)  

Superspreading

(a). Dynamics of an aqueous AOT drop spreading over a hydrophobic surface. The line is a fit to a power-law evolution R = C t1/10 yielding the prefactor C. (b) and (c) Dynamics of aqueous trisiloxane drops. The lines are fits to a power-law evolution R = C ta yielding a power of (b) 0.16 and (c) 1, depending upon the trisiloxane concentration       Photograph of the spreading trisiloxane solution droplet at the highest surfactant concentration used here. The radius of the droplet is 3 mm.   Power a from the evolution of the radius R = C ta for the 'superspreading' of the trisiloxane solutions.   Langmuir, 18 (2002) 10486

The dynamics of the spreading of a drop of a liquid or of a solution of surfactant in water are similar and well-understood, excepted for surfactants called superspreaders. Marangony effects are probably at the origin of the large increase of the velocity of the spreading.

Inhibition of droplet rebound on hydrophobic substrates

It was shown that the inhibition of the rebound of drops falling on a hydrophobic surface by a small amount of polymers results from the elongational viscosity (collaboration ENS/Rhodia). Typical photographic sequence of an aqueous drop striking a hydrophobic surface. a) pure water. b) dilute PEO solution (M=4 106, at 0.1 g/l). The lower ghost images are reflections from the top and/or bottom surface of the solid glass substrate.     Nature 405 (2000) 773

pure water

dilute PEO solution

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