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.

Gel-based self-propelling particles get programmed to dance.

Abstract: We present a class of gel-based self-propelling particles moving by the Marangoni effect in an oscillatory mode. The particles are made of an ethanol-infused polyacrylamide hydrogel contained in plastic tubing. These gel boats floating on the water surface exhibit periodic propulsion for several hours. The release of ethanol from the hydrogel takes place beneath the liquid surface. The released ethanol rises to the air–water interface by buoyancy and generates a self-sustained cycle of surface tension gradient driven motion. The disruption of the ethanol flux to the surface by the bulk flows around the moving particle results in their pulsating motion. The pulse interval and the distance propelled in a pulse by these gel floaters were measured and approximated by simple expressions based on the rate of ethanol mass-transfer through and out of the hydrogel. This allowed us to design a multitude of particles performing periodic steps in different directions or at different angles of rotation, traveling in c...

Thermocapillary actuation by optimized resistor pattern: bubbles and droplets displacing, switching and trapping

Abstract: We report a novel method for bubble or droplet displacement, capture and switching within a bifurcation channel for applications in digital microfluidics based on the Marangoni effect, i.e. the appearance of thermocapillary tangential interface stresses stemming from local surface tension variations. The specificity of the reported actuation is that heating is provided by an optimized resistor pattern (B. Selva, J. Marchalot and M.-C. Jullien, An optimized resistor pattern for temperature gradient control in microfluidics, J. Micromech. Microeng., 2009, 19, 065002) leading to a constant temperature gradient along a microfluidic cavity. In this context, bubbles or droplets to be actuated entail a surface force originating from the thermal Marangoni effect. This actuator has been characterized (B. Selva, I. Cantat, and M.-C. Jullien, Migration of a bubble towards a higher surface tension under the effect of thermocapillary stress, preprint, 2009) and it was found that the bubble/droplet (called further element) is driven toward a high surface tension region, i.e. toward cold region, and the element velocity increases while decreasing the cavity thickness. Taking advantage of these properties three applications are presented: (1) element displacement, (2) element switching, detailed in a given range of working, in which elements are redirected towards a specific evacuation, (3) a system able to trap, and consequently stop on demand, the elements on an alveolus structure while the continuous phase is still flowing. The strength of this method lies in its simplicity: single layer system, in situ heating leading to a high level of integration, low power consumption (P < 0.4 W), low applied voltage (about 10 V), and finally this system is able to manipulate elements within a flow velocity up to 1 cm s−1.

Flow structure and dynamic particle accumulation in thermocapillary convection in a liquid bridge

Abstract: Thermocapillary convection is induced in a liquid bridge by a nonuniform surface tension distribution caused by an axial temperature difference. A toroidal vortex is formed by the thermocapillary force over the free surface. The induced flow is visualized by using fine particles as tracers. At a sufficiently high Marangoni number, three-dimensional standing and traveling oscillatory flows appear, and under certain flow conditions, the tracer particles form particle accumulation structures (PAS). In the present study, the conditions for the occurrence of PAS have been carefully investigated with focus on the spiral loop PAS (SL-PAS) that appears when the flow exhibits a traveling mode. The particles gather along a closed spiral loop that winds itself around the toroidal vortex. Observed from above, the spiral loop looks as if it is rotating azimuthally. The number of spirals corresponds with the azimuthal wave number of the traveling wave and each spiral consists of either single or double turns. The azimuthal traveling direction of the particles trapped on the SL-PAS is opposite to that of the SL-PAS pattern and of the hydrothermal wave under the presently focused conditions. By varying particle diameter and density within a certain range, it was revealed that the SL-PAS appears almost independently of the particle properties. The path line of each particle trapped in the SL-PAS is different from the shape of the SL-PAS itself. The Stokes number of a particle is examined and found to be much smaller than unity. Furthermore, a structure similar to the SL-PAS was also visualized by injecting colored dye. Thus, the shape of the SL-PAS is primarily determined not by the particle-particle interaction but by the flow field itself.