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.

Marangoni effect visualized in two-dimensions Optical tweezers for gas bubbles.

Abstract: In the report we demonstrate how, using laser light, effectively trap gas bubbles and transport them through a liquid phase to a desired destination by shifting the laser beam position. The physics underlying the effect is complex but quite general as it comes from the limited to two-dimension, well-known, Marangoni effect. The experimental microscope-based system consists of a thin layer of liquid placed between two glass plates containing a dye dissolved in a solvent and a laser light beam that is strongly absorbed by the dye. This point-like heat source locally changes surface tension of nearby liquid-air interface. Because of temperature gradients a photo-triggered Marangoni flows are induced leading to self-amplification of the effect and formation of large-scale whirls. The interface is bending toward beam position allowing formation of a gas bubble upon suitable beam steering. Using various techniques (employing luminescent particles or liquid crystals), we visualize liquid flows propelled by the tangential to interface forces. This helped us to understand the physics of the phenomenon and analyze accompanying effects leading to gas bubble trapping. The manipulation of sessile droplets moving on the glass surface induced via controlled with laser light interface bending (i.e. “droplet catapult”) is demonstrated as well.

Effect of mass transfer on the film drainage between colliding drops.

Abstract: The influence of mass transfer on the drainage behaviour of the thin liquid film between two drops immersed in another liquid colliding at constant approach velocity has been studied experimentally. The liquid–liquid system used is glycerol in silicone oil. The transferred solute is acetone and the volume concentration difference across the interface ranges from 1 to 5%. The film thickness evolution has been measured using a laser interferometry technique. The direction of mass transfer (from the drops towards the film phase and inversely) has been investigated and the results compared to the case with no mass transfer [E. Klaseboer, J.P. Chevaillier, C. Gourdon, O. Masbernat, J. Colloid Interface Sci. 229 (2000) 274–285]. When the solute transfers from the drops towards the continuous phase, the drainage rate is significantly higher than in the case with no mass transfer. This result is interpreted as a consequence of the mass transfer induced surface mobility in the film region (the so-called Marangoni effect) due to localized surface tension differences. This effect has been demonstrated by the visualization of the flow patterns in the drops and in the film phase (using a particle tracer technique). In this case, the slope of the film height as a function of time seems to be independent of the approach velocity condition imposed on the drop and appears to be controlled by the interfacial tension gradient. In the opposite case, when the solute transfers from the continuous phase towards the drops, the film drainage rate is lowered with respect to the case of no mass transfer, goes to zero or even changes its sign depending on the mass transfer intensity. The results also show that in the range of solute concentration studied, the effect of mass transfer on the film drainage process takes place at large distances compared to the scales at which lubrication theory is valid.

Regimes of thermocapillary migration of droplets under partial wetting conditions

Abstract: We study the thermocapillary migration of two-dimensional droplets of partially wetting liquids on a non-uniform heated substrate. An equation for the thickness profile of the droplet is derived by employing lubrication approximations. The model includes the effect of a non-zero contact angle introduced through a disjoining― conjoining pressure term. Instead of assuming a fixed shape for the droplet, as in previous works, here we allow the droplet to change its profile with time. We identify and describe three different regimes of behaviour. For small contact angles, the droplet spreads into a long film profile with a capillary ridge near the leading edge, a behaviour that resembles the experiments on Marangoni films reported by Ludviksson & Lightfoot (Am. Inst. Chem. Eng. J., vol. 17, 1971, pp. 1166). For large contact angles, the droplet moves as a single entity, weakly distorted from its static shape. This regime is the usual one reported in experiments on thermocapillary migration of droplets. We also show some intriguing morphologies that appear in the transition between these two regimes. The occurrence of these three regimes and their dependence on various parameters is analysed.

Instabilities of dynamic thermocapillary liquid layers with magnetic fields

Abstract: We present a linear-stability analysis for the transition from a steady, two-dimensional thermocapillary convection in a liquid-metal layer to a periodic, three-dimensional flow involving hydrothermal waves which propagate in the direction normal to the plane of the base flow. There is a uniform magnetic field applied parallel to the free surface in the plane of the base flow, and there is a linear temperature gradient along the free surface in the base flow. The ratio of the layer's length to its depth, 2L, is large. The magnetic Reynolds number is small. A key parameter is λ, the ratio of the large Hartmann number based on depth to L