THICKENING FACTOR IN MARANGONI COATING

We have recently shown that a wire, and more generally a solid, drawn out of a solution containing surfactants entrains a thicker film than one drawn out of a pure liquid (Marangoni coating). The thickening fac tor, generally of order 2, was found to be independent of the capillar y number (for surfactant concentration of the order of the cmc) but de pends on the wire radius: the thinner the wire, the larger the thicken ing. After summarizing these results, we propose a model for understan ding this effect, which is shown to result from a balance between conv ection and adsorption. Finally, a scaling form is proposed for the thi ckening factor.