Marangoni Flows

Film Rupture. Another general mechanism by which foams evolve is the coalescence of neighboring bubbles via film mpture. This occurs if the nature of the surface-active components is such that the repulsive interactions and Marangoni flows are not sufficient to keep neighboring bubbles apart. Bubble coalescence can become more frequent as the foam drains and there is less Hquid to separate neighbors. Long-Hved foams can be easHy... 

Nikolov AD, Wasan DT, Chengara A, Koczo K, Policello GA, Kolossvary I (2002) Superspreading driven by Marangoni flow. Adv Colloid Interface Sci 96 325-338... 

When surface tension differences appear or are produced between some points or some small regions of an interface, the flow produced is called the Marangoni flow or flow with Marangoni effect. The Marangoni number, used to characterize the flow shown on Fig. 6.9, is a combination of the Reynolds number, the Weber number and the Schmidt number ... 

Single crystal silicon is one of the important fundamental materials for the modern photovoltaic industry. The Czochralski method of growing single crystal silicon is affected by the thermocapillary convection. Temperature and concentration gradients at the free surface of the melt give rise to surface tension-driven Marangoni flow, which can lead to crystal defects, if it is sufficiently large. 

Capillarity phenomena are everyday occurrences that result from the existence of surface tension or interfacial tensions. In addition to the static phenomena discussed herein, surface tension and capillarity are also responsible for numerous dynamic phenomena that may result from localized gradients in temperatures or in compositions the study of dynamic capillary phenomena (e.g., Marangoni flows, Benard cells) is the subject of much literature coverage and is beyond the scope of this survey. 

Fig. 3.9. Inhomogeneous density of adsorbed species due to the action of a hydrodynamic force initiates a Marangoni flow in the opposite direction after Edwards et al. (1992)...

Fig. 3.11. Opposite direction of hydrodynamic shear stress and Marangoni flow - adsorption...

An analysis of the complex problem of liquid flow and adsorption kinetics was given by Ziller et al. (1985) (cf. Section 4.8). The system of linearised hydrodynamic and transport equations was solved numerically under the assumption of different boundary conditions. The results show that a quantitative interpretation of inclined plate experiments requires a time consuming analysis. However, a rather good approximation is possible by neglecting the Marangoni flow induced by surface tension gradients against the flow direction. 

Surface self-diffusion is the two-dimensional analogue of the Brownian motion of molecules in a liquid bulk. Measurements of self-diffusion have to be performed in complete absence of any Marangoni flow caused by surface tension differences. Such experimental conditions are best established in an insoluble monolayer where one part consists of unlabelled and the other of radio-tracer labelled molecules. The movement of molecules within the surface monolayer can be now observed by using a Geiger-Miiller counter. There are possible effects of liquid convective flow in the sublayer which was discussed for example by Vollhardt et al. (1980a). With e special designed apparatus Vollhardt et al. (1980b) studied the self-difihision of different palmitic and stearic acid and stearyl alcohol and obtained self-diffusion coefficients between l-i-4 lO cm /s. 

Perturbation of the lamellae whether due to external shocks, the oil imbibition, foam flow, or lamella expansions and contractions (Marangoni flow). 

Marangoni Flow Liquid flow in response to a gradient in surface (or interfacial) tension. See also Marangoni Effect. 

C. Pan and T. N. Lin, Marangoni Flow Effect in Nucleate Boiling Near Critical Heat Flux, in Int. Comm. Heat Mass Transfer (16) 475-486,1989. 

Since the value of the surface tension varies with tanperature and with the contamination of the interface by the possible presence of surfactant molecules, each change of these parameters can lead to a Marangoni flow, which is referred, respectively, as thermocapillary or solute-capillary flow. 

It is straightforward that the evaporative flux at the contact line will result in radial flow inside of a droplet to compensate the liquid loss at the contact line. However, the flow inside of an evaporating droplet turns out to be more complicated. It was found that radial flow, which facilitates coffee-ring formation, and Marangoni flow, which reverses coffee-ring formation, could occur during evaporation and ultimately lead to entirely different deposition patterns. 

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