Effect of insoluble surfactants on a thermocapillary flow

Abstract

The thermocapillary effect, arising flow due to a temperature gradient along a fluid interface, is the dominant effect in some industrial and microfluidic processes and must be studied in order to optimize them. In this work, we analyze how insoluble surfactants adsorbed at the interface can affect such a flow. In particular, we analyze the case where the thermocapillary flow is induced at the air-water interface by locally heating it with an infrared laser, setup that is used to manipulate floating particles through the generated flow.Since water is a polar fluid, the air-water interface is easily polluted by surfactants. We developed a numerical model considering the uncontrolled presence of surfactants, which evidences that the effect of the surface contamination cannot be neglected, even for small surfactants concentration. The results of this numerical model were compared with different experimental measurements: particle tracking velocimetry, convection cell radius measurements and thermography of the surface. All the experimental observations agree with the numerical model with the initial surface contamination being a fitting parameter. The model was then validated comparing its results with measurements for which a known quantity of surfactant was added to the interface. Finally, an analytical model was developed to explain the effects of the governing parameters, which agrees with the simulations and the experimental results. The developed models give us insights towards the miniaturization of the manipulation platform.

Pose Control of Millimeter-Scale Objects in a Laser-Powered Thermocapillary Manipulation Platform

“…where C d is the viscous drag coefficient, m is the mass of the particle, U is the thermocapillary flow velocity at the point P, Ṗ and P are the particle velocity and acceleration, respectively. As it has been shown in a previous work [36], the laser-powered thermocapillary flow surface velocity magnitude is inversely proportional to the distance to the laser spot and the flow direction is always away from the laser spot. Thus,…”

“…2a. This local heating causes a local temperature increase, which gives place to a thermocapillary flow around the laser spot due to the Marangoni effect [36]. The resulting flow is divergent from the laser spot at the interface, thus pushing floating objects away from the spot.…”

Controlled transitions between metastable states of 2D magnetocapillary crystals

“…Additionally, an infrared (IR) laser is pointed towards the recipient from above, enabling to locally heat the air–water interface. The energy of the laser is absorbed by the water, locally increasing the interface temperature, and thus generating an interfacial thermocapillary flow 27 , as schematized in Fig. 5 b.…”

Interfacial Flows and Interfacial Shape Modulation Controlled by the Thermal Action of Light Energy

“…Recently, a number of theoretical, numerical, and experimental studies [73,[76][77][78] have been performed to understand the mechanism of influence of surfactant adsorbed at the liquid-air interface on the nature of the thermocapillary flows.…”

“…The study [76] reports the results of an experimental and numerical investigation of the influence of an insoluble oleic acid surfactant added to the water-air interface on the development of axisymmetrical thermocapillary flow in the water layer of 7.5 mm thick. The thermocapillary flow was induced by heating of the water with the IR laser beam (λ = 1455 nm, 2w 0 = 1.26 mm, P = 40 mW).…”