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Fluctuation Interactions between Soft Interfaces in Complex Systems – FISICS

Submission summary

Statistical physics tells us that when a system’s dimensions are reduced, to the order of the correlation length (ksi) of its compositional fluctuations, its free energy shows finite size effects. Manifestations of these effects are for instance the critical Casimir effect (where the large fluctuations in a critical fluid are modified by the presence of hard walls), as well as the finite size corrections to the surface tension of small drops first predicted by Tolman in 1949. In nano-scale systems, finite size effects modify the properties of interfaces and recent results have shown deviations from the classical theory based on two fluids, deterministic, hydrodynamics with sharp interfaces. The surface tension (G) is crucial to many non-equilibrium phenomena such as evaporation and nucleation, as well as two-fluid hydrodynamic instabilities. In nano-scale systems, finite size effects will lead to variations in surface tension and thus will modify these non-equilibrium phenomena. Finite size effects at interfaces become important at scales where the size of the objects is of the order of the thermal length Lt = SQRT (kT/G). In most systems G = kT/a.a, where a is a molecular length scale, and thus the regime where finite size effects become important is difficult to attain experimentally, especially if one wishes to visualize surface dynamics. However, in phase-separated near critical binary mixtures Lt, which equals a few ksi, can thus be made large as we approach the critical point (ksi diverges when the critical point is neared). This means that finite size scaling effects can be investigated in objects large enough to be studied optically.
Here we will use near critical binary mixtures as model systems where fluctuations, and thus finite size, effects are amplified. The influence of such effects on evaporation and hydrodynamic instabilities will be studied experimentally and theoretically. This will uncover new fundamental phenomena due to fluctuation and finite size effects at soft interfaces in two-fluid systems. The major innovation of the FISICS project, which combines experimental and theoretical work, is thus its focus on the effect of fluctuations in near critical phase separated liquids out-of-equilibrium in the presence of soft liquid interfaces. Both instabilities and finite size effects are dependent on geometry and a key point in FISICs is our ability to vary the geometry of the objects studied using the optical radiation pressure. Spherical droplets will be produced to study evaporation and the relaxation dynamics of deformed droplets, while the properties of near axisymmetric geometries will be analyzed via the break up and instabilities of ligaments and jets. The results of our project may open up new perspectives in nano-fluidics, suggesting possible mechanisms for nano-jet break up and the production of nano-drops, as well as nucleation theory.

Project coordination

Jean-Pierre DELVILLE (Laboratoire Ondes et Matière d'Aquitaine)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

LOMA Laboratoire Ondes et Matière d'Aquitaine
ENS de Lyon Laboratoire de Physique, ENS Lyon
CNRS DR12_IRPHE UMR7342 Centre National de la Recherche Scientifique délégation Provence et Corse_Institut de Recherche sur les Phénomènes Hors Equilibre

Help of the ANR 412,096 euros
Beginning and duration of the scientific project: October 2015 - 48 Months

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