MAIN RESEARCH INTERESTS of the GROUP

Matière molle, Instabilités et transitions de phases

(soft matter, instabilities and phase transitions)  

 

Rheology of complex fluids

Polymer solutions: elongational viscosity

 

Finite-time singularity

when a droplet detaches

from a capillary

(Water)

 

Inhibition of the finite

time singularity by

the elongationnal viscosity

(PEO Solution)

 

Phys. Rev. Lett. 86 (2001) 3558

 

Extrusion instability

Extrusion instabilities are observed when polymer melts are pressed out of a hole. We have shown that these result from the normal forces that the viscoelastic fluid develops in a shear flow.

 

Phys. Rev. Lett. 90 (2003) 024502

Phys. Rev. Lett. , to appear

 

Large deformations of giant floppy vesicules in shear flow

Phase-contrast micrographs of a 7.6 mM AOT solution at [NaCl] = 0.075 M;

(a) at rest, spherical as well as tubular vesicles are observed;

( b) under a continuous shear of 0.5 s-1 very long and thin filamentary bilayer tubes are observed, forming an entangled structure. The tubes appear to be under tension since they are stretched in the flow field. Arrows indicate transitions from thick to thin filaments. Bars are 30 mm.

Phys. Rev. Lett 81 (1998) 4271

 

Viscosity of the solution as a function of time. For low (closed symbols, 0.5 s-1) and high (open symbols, 30 s-1) shear. The white line is a fit to an exponential increase

 

 

Anti-thixotropic behavior of a lamellar phase of AOT

_____

600 mm

 "Onion" defects formed by shearing a lamellar phase La.

NaCl=1.3%, shear rate=40 s-1 (shearing time : 650s, 790s, 875s, 969s, 1005s, 1060s,)

 

 

At low salinities and at equilibrium, the lamellar phase contains many onion defects and is viscous ([La]0)

At large salinities and at equilibrium, a low viscosity plane lamellar phase, La, is found.

Under shear, the latter shows a sudden transition to a viscoelastic gel, with a texture and a viscosity similar to that of the onion phase

 

Phys. Rev. Lett. 84 (2000) 1335

 

Shear induced first-order transition

 

Nucleation and growth of a Lamellar phase in a Sponge phase induced by shear (shear rate 780s-1)

 

Phys Rev. Lett. 86 (2001) 938

 

 

Relaxation of the shear induced phases

 

Coalescence of two bubbles made of a film of lamellar phase out of equilibrium in a sponge phase at equilibrium. The lamellar phase is obtained by shearing the sponge phase.

 

J. Phys.: Cond. Matter 14 (2002) 4785

  

Rheology of simple fluids

The hydraulic jump

In one dimension, between two glass plates

 

 

 

In two dimensions

 

 

 

 

 

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