THE THICKNESS OF SURFACE-TENSION-GRADIENT-DRIVEN SPREADING FILMS

We present here a new interpretation of the origin of the thickness of surface-tension-gradient-driven spreading films. Besides the already known regime, where this thickness is controlled by the influence of gravity and is proportional to the surface tension gradient, we show the existence of another regime, where the curvature of the meniscus, out of which the film climbs, must be taken into account, and the thickness is proportional to the square of the surface tension gradient. This situation corresponds to low surface tension gradients, or equivalently to highly curved menisci. This theory is successfully used to explain the differences observed between two previously published papers (Ludviksson and Lightfoot, AIChE J. 17, 1166 (1971); Cazabat et al., Nature 346, 824 (1990)), and its predictions are checked by new experiments. © 1993 Academic Press, Inc.