MAIN RESEARCH INTERESTS of the GROUP

"Matière molle, Instabilités et transitions de phases"

(soft matter, instabilities and phase transitions)

 

 

WETTING TRANSITIONS

This work benefited from financial contributions from European commission trough:

CONTRACT NUMBER: JOF3-CT95-0013 (JOULE PROGRAM). Estimation of reserves potential for near-critical systems

CONTRACT NUMBER: JOF3-CT97-0042 (JOULE PROGRAM). Estimation of reserves potential for near-critical systems-2

CONTRACT NUMBER: ERBFMRXCT98-0171 (TMR PROGRAM). Foam stability and wetting transitions.

The results of the experiments establish, for the first time, that the wetting transition can come in three flavors. The schematic drawings below summarize the results of the experiments: the wetting transition can be:

 

  • 1- Discontinuous: there is a singularity in the first derivative of the surface free energy with respect to temperature and we consequently speak of a first-order wetting (FOW) transition. The film thickness jumps discontinuously from a microscopically thin to a thick film at the wetting transition temperature Tw. A hysteresis can be observed.

Phys. Rev. Lett. 84 (2000) 4461

 

 

  • 2- Discontinuous followed by a continuous divergence of the film thickness. The divergence is due to a change in sign of the net effect of the long-range van der Waals forces in the interaction energy between the two interfaces. As the transition is continuous and due to the long-range forces, this transition is called the Long-Range Critical Wetting (LRCW) transition. Collaboration IFP and J. Indekeu.

Phys. Rev. Lett. 80 (1998) 3992

 

 

  • 3- Completely continuous. This is an exceptional situation for which the long-range van der Waals forces can be neglected. As the transition is continuous and due to short-range forces, this transition is called the Short-Range Critical Wetting (SRCW) transition.

Nature 400 (1999) 737

Wetting of a drop of methanol at the free surface of different alkanes

 

 

At room temperature, the contact angle is small for undecane, large for hexane. It is close to 90° for octane.

Wetting for nonane appears close to the bulk critical point and is continuous (short-range critical wetting)

 

Nature 400 (1999) 737

Phys. Rev. Lett. 87 (2001) 176103

J. Chem. Phys. 114 (2001) 2784

 

Wetting and thermal fluctuations

 

Film of alkane on water

 

 

Thickness of a wetting film of methanol at the free surface of cyclohexane close to the bulk critical point

 

Thermal fluctuations increase the thickness of a mesoscopic wetting film.

 

 

 

  • This can be obtained by addition of a surfactant (AOT) which strongly decreases the water/alkane interfacial tension.

 

Europhys. Lett. 55 (2001) 827

 

 

 

 

 

 

 

 

 

 

  • This can be obtained by approaching a bulk critical point: the film thickness diverges as t-b* with b*=0.23±0.06. We predict b*=b/3 (b the usual bulk-order parameter critical exponent). Collaboration with O. Parry (London) M. Telo da Gama (Lisbon) and the group of G. Wegdam (Amsterdam)

 

 

Phys. Rev. Lett. 89 (2002) 096101

 

 

 

 

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