Surface tension drainage induced

The mass-transfer-induced Marangoni effect This effect stabilizes the film when liquid surface tension increases due to mass transfer (i.e., the less-volatile component has a higher surface tension than the more-volatile component). The liquid film just between two adjacent vapor bubbles is closer to equilibrium than the liquid at some distance from these vapor bubbles, and therefore has a higher surface tension than the bulk of the liquid (Fig. 14.96). The surface-tension gradient sucks liquid into the film between the two bubbles, thus counteracting drainage. 

Surface tension gradients can induce drainage rates in excess of that expected for simple viscous flow if the low MW components have higher surface tensions than the undistilled liquid, e.g., alkyl-substituted aromatics This reverse flow is illustrated in Fig. 16 for a liquid mixture of isomeric amylnaphthalenes. In this case, evaporation of low MW components from the primary film results in a lower surface tension and a surface flow from the primary film onto the secondary film. Distillation of the amylnaphthalene essentially eliminated this reverse flow (Fig. 16). 

The Marangoni effect, that is, the retardation of thin-fihn drainage by induced tension gradients, is believed to play an important role in emulsion stabilization (31). The most severe case of Marangoni s effect is, of course, one that involves immobile surfaces. The associated drainage time can be estimated from the Reynolds equation (31) ... 

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