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.

A floating self-propelling liquid marble containing aqueous ethanol solutions

Abstract: A liquid marble is a droplet coated with hydrophobic particles. A floating liquid marble is a unique reactor platform for digital microfluidics. The autonomous motion of a liquid marble is of great interest for this application because of the associated chaotic mixing inside the marble. A floating object can move by itself if a gradient of surface tension is generated in the vicinity of the object. This phenomenon is known as the Marangoni solutocapillary effect. We utilized a liquid marble containing a volatile substance such as ethanol to generate the solutocapillary effect. This paper reports a qualitative study on the operation conditions of liquid marbles containing aqueous ethanol solutions in autonomous motion due to the Marangoni solutocapillary effect. We also derive the scaling laws relating the dynamic parameters of the motion to the physical properties of the system such as the effective surface tension of the marble, the viscosity and the density of the supporting liquid, the coefficient of diffusion of the ethanol vapour, the geometrical parameters of the marble, the speed, the trajectory and the lifetime of the autonomous motion. A self-driven liquid marble has the potential to serve as an effective digital microfluidic reactor for biological and biochemical applications.

Effect of surfactants on film flow down a periodic wall

Abstract: The effect of an insoluble surfactant on the gravity-driven flow of a liquid film down an inclined wall with periodic undulations or indentations is investigated in the limit of vanishing Reynolds number. A perturbation analysis for walls with small-amplitude sinusoidal corrugations reveals that the surfactant amplifies the deformation of the film surface, though it also renders the film thickness more uniform over the inclined surface. The effect of the surfactant is most significant when the film thickness is less than half the wall period. To explain the deforming influence of the surfactant, a linear stability analysis of film flow down an inclined plane is undertaken for two-dimensional perturbations. The results reveal the occurrence of a Marangoni normal mode whose rate of decay is lower than that of the single mode occurring in the absence of surfactants. Numerical methods based on a combined boundary-element/finite-volume method are implemented to compute flow down a periodic wall with large-amplitude corrugations or semi-circular depressions. In the case of a wavy wall, it is found that the shape of the film surface is described well by the linear perturbation expansion for small and moderate wave amplitudes. Streamline patterns reveal that, although the effect of the surfactant on the shape of the film surface is generally small, Marangoni tractions may have a profound influence on the kinematics by causing the onset of regions of recirculating flow.

Surface and buoyancy driven free convection

Abstract: A system of two interfacing immiscible fluids subject to an imposed temperature difference in a gravity field is considered. The fluids, the gravity level, the temperature difference and the extension of the interface are arbitrary. An order of magnitude analysis is applied to determine: (i) the types of flow regimes that can be attained in natural, Marangoni or combined free convection; (ii) how the problem's data identify which type of free convection and of flow regime prevails in each specific case.

The contribution of chemistry to new Marangoni mass-transfer instabilities at the oil/water interface

Abstract: Spontaneous interfacial motions appear at an interface between two immiscible phases in a state far from equilibrium, e.g. an aqueous phase of an organic acid or a complex ion and an organic phase of a long-chain surfactant molecule. The instabilities observed are related to variations in the interfacial tension. It is shown that they resemble the well known Marangoni effect by considering interfacial convection and the coupling between diffusion and convection fluxes, but they differ by the presence of chemical reactions. The notion of assisted desorption is defined in order to interpret the experiments.The analysis of this phenomenon could be useful in determining the optimal conditions for obtaining convective interfacial transfer to enhance liquid–liquid extraction processes.

Marangoni-driven flower-like patterning of an evaporating drop spreading on a liquid substrate.

Abstract: Drop motility at liquid surfaces is attracting growing interest because of its potential applications in microfluidics and artificial cell design. Here we report the unique highly ordered pattern that sets in when a millimeter-size drop of dichloromethane spreads on an aqueous substrate under the influence of surface tension, both phases containing a surfactant. Evaporation induces a Marangoni flow that forces the development of a marked rim at the periphery of the spreading film. At some point this rim breaks up, giving rise to a ring of droplets, which modifies the aqueous phase properties in such a way that the film recoils. The process repeats itself, yielding regular large-amplitude pulsations. Wrinkles form at the film surface due to an evaporative instability. During the dewetting stage, they emit equally spaced radial strings of droplets which, combined with those previously expelled from the rim, make the top view of the system resemble a flower.