Marangoni effect

About: Marangoni effect is a research topic. Over the lifetime, 5336 publications have been published within this topic receiving 98562 citations. The topic is also known as: Gibbs–Marangoni effect.

On the Faraday instability in a surfactant-covered liquid

Abstract: The formation of standing waves at the surfactant-covered free surface of a vertically-vibrated liquid is analyzed in this work. Assuming that the surfactants are insoluble and the effects of lateral boundaries are negligible, linear stability analysis and Floquet theory are applied to the governing equations. A recursion relation involving the temporal modes of the free-surface deflection and surfactant concentration variation results, and is solved to determine the critical vibration amplitude needed to excite the standing waves and the corresponding critical wave number. It is found that the critical vibration amplitude shows a minimum with respect to the Marangoni number, meaning that surfactants can potentially lower the value of the critical amplitude relative to its value for an uncontaminated free surface. The critical wave number, however, is found to be an increasing function of the Marangoni number. Analysis of the phase-angle difference between the free-surface deflection and the surfactant concentration variation suggests that the minimum in the critical amplitude arises because the Marangoni flows help produce a velocity field near the free surface similar to that which would be present if the liquid were inviscid.

Massive amplification of surface-induced transport at superhydrophobic surfaces.

Abstract: We study electro- and diffusio-osmosis of aqueous electrolytes at superhydrophobic surfaces by means of computer simulation and hydrodynamic theory. We demonstrate that the diffusio-osmotic flow at superhydrophobic surfaces can be amplified by more than 3 orders of magnitude relative to flow in channels with a zero interfacial slip. By contrast, little enhancement is observed at these surfaces for electro-osmotic flow. This amplification for diffusio-osmosis is due to the combined effects of enhanced slip and ion surface depletion or excess at the air-water interfaces on superhydrophobic surfaces. This effect is interpreted in terms of capillary driven Marangoni motion. A practical microfluidic pumping device is sketched on the basis of the slip-enhanced diffusio-osmosis at a superhydrophobic surface.

Dissipative Korteweg–de Vries description of Marangoni–Bénard oscillatory convection

Abstract: For a horizontal liquid layer open to air and heated either from the air side or the liquid side, threshold values for the onset of oscillatory interfacial instability are provided, as well as the nonlinear evolution equation describing the deformable open surface. The latter equation is the dissipation‐modified Korteweg–de Vries evolution equation for solitary excitations in the liquid layer.

The dynamics of a viscous soap film with soluble surfactant

Abstract: Nearly two decades ago, Couder (1981) and Gharib & Derango (1989) used soap films to perform classical hydrodynamics experiments on two-dimensional flows. Recently soap films have received renewed interest and experimental investigations published in the past few years call for a proper analysis of soap film dynamics. In the present paper, we derive the leading-order approximation for the dynamics of a flat soap film under the sole assumption that the typical length scale of the flow parallel to the film surface is large compared to the film thickness. The evolution equations governing the leading-order film thickness, two-dimensional velocities (locally averaged across the film thickness), average surfactant concentration in the interstitial liquid, and surface surfactant concentration are given and compared to similar results from the literature. Then we show that a sufficient condition for the film velocity distribution to comply with the Navier–Stokes equations is that the typical flow velocity be small compared to the Marangoni elastic wave velocity. In that case the thickness variations are slaved to the velocity field in a very specific way that seems consistent with recent experimental observations. When fluid velocities are of the order of the elastic wave speed, we show that the dynamics are generally very specific to a soap film except if the fluid viscosity and the surfactant solubility are neglected. In that case, the compressible Euler equations are recovered and the soap film behaves like a two-dimensional gas with an unusual ratio of specific heat capacities equal to unity.