title: MHz Ultrasound Induced Roughness of Fluid Interfaces.
abstract: The interface between two fluids is never flat at the nanoscale, and this is important for transport across interfaces. In the absence of any external field, the surface roughness is due to thermally excited capillary waves possessing subnanometric amplitudes in the case of simple liquids. Here, we investigate the effect of ultrasound on the surface roughness of liquid-gas and liquid-liquid interfaces. Megahertz (MHz) frequency ultrasound was applied normal to the interface at relatively low ultrasonic pressures (<0.6 MPa), and the amplitudes of surface fluctuations have been measured by light reflectivity and ellipsometry. We found a dramatic enhancement of surface roughness, roughly linear with intensity, with vertical displacements of the interface as high as 50-100 nm. As a consequence, the effective contact area between two fluids can be increased by ultrasound. This result has a clear impact for enhancing interface based processes such as mass or heat transfer.
authors.affiliation: Laboratoire Charles Coulomb (L2C), UMR 5221 CNRS-Univ. Montpellier, Montpellier F-34095, France.|Institut de Chimie Séparative de Marcoule, UMR 5257 (CEA, CNRS, UM, ENSCM), BP 17171, 30207 Cedex Bagnols-sur-Cèze, France.
authors.forename: Rym
authors.initials: R
authors.lastname: Boubekri
authors.affiliation: Laboratoire Charles Coulomb (L2C), UMR 5221 CNRS-Univ. Montpellier, Montpellier F-34095, France.
authors.forename: Michel
authors.initials: M
authors.lastname: Gross
authors.affiliation: Laboratoire Charles Coulomb (L2C), UMR 5221 CNRS-Univ. Montpellier, Montpellier F-34095, France.
authors.forename: Martin
authors.initials: M
authors.lastname: In
authors.affiliation: Institut de Chimie Séparative de Marcoule, UMR 5257 (CEA, CNRS, UM, ENSCM), BP 17171, 30207 Cedex Bagnols-sur-Cèze, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Diat
authors.affiliation: Laboratoire Charles Coulomb (L2C), UMR 5221 CNRS-Univ. Montpellier, Montpellier F-34095, France.
authors.forename: Maurizio
authors.initials: M
authors.lastname: Nobili
authors.affiliation: Max-Planck-Institute of Colloids and Interfaces , Am Mühlenberg, 14476 Potsdam, Germany.
authors.forename: Helmuth
authors.initials: H
authors.lastname: Möhwald
authors.affiliation: Laboratoire Charles Coulomb (L2C), UMR 5221 CNRS-Univ. Montpellier, Montpellier F-34095, France.
authors.forename: Antonio
authors.initials: A
authors.lastname: Stocco