Film Deposition in Non-Wetting Tubes: An Experimental Film Thickness Law

Deposition of a liquid film on non-wetting tubular surfaces gives rise to the unexpected behavior of simultaneously coexisting thick and thin films. Experiments show that a discontinuity in the film thickness, a jump between the thick and thin films being laid from the meniscus towards the bounding moving contact line, occurs after a considerably thicker than the expected Bretherton film is deposited. Bretherton assumed the film to be uniform and, unlike the case of a non-wetting surface, the visco-capillary deposition process was not affected by the presence of a contact line. In reality this phenomenon lies at the confluence between a dewetting process and the deposition itself, being the result of the influence claimed by the dynamics of the zone adjacent to the moving contact line. The film thickness is calculated directly from the experimental data and a correlation is obtained by matching the measured and the theoretical shock velocities associated with the hydraulic jump. The non-wetting film is significantly thicker than Bretherton’s prediction and follows in turn a different law which is determined experimentally. The non-wetting film thickness is found to vary as $hR4/3$⁠, $hR$ being the Ca-dependent non-dimensional Bretherton film thickness.