Dynamics of spontaneous spreading with evaporation on a deep fluid layer
- 1 January 1998
- journal article
- research article
- Published by AIP Publishing in Physics of Fluids
- Vol. 10 (1), 23-38
- https://doi.org/10.1063/1.869546
Abstract
The spontaneous spreading of a thin volatile film along the surface of a deep fluid layer of higher surface tension provides a rapid and efficient transport mechanism for many technological applications. This spreading process is used, for example, as the carrier mechanism in the casting of biological and organic Langmuir–Blodgett films. We have investigated the dynamics of spontaneously spreading volatile films of different vapor pressures and spreading coefficients advancing over the surface of a deep water support. Laser shadowgraphy was used to visualize the entire surface of the film from the droplet source to the leading edge. This noninvasive technique, which is highly sensitive to the film surface curvature, clearly displays the location of several moving fronts. In this work we focus mainly on the details of the leading edge. Previous studies of the spreading dynamics of nonvolatile, immiscible thin films on a deep liquid layer have shown that the leading edge advances in time as as predicted by laminar boundary layer theory. We have found that the leading edge of volatile, immiscible spreading films also advances as a power law in time, , where . Differences in the liquid vapor pressure or the spreading coefficient seem only to affect the speed of advance but not the value of the spreading exponent, which suggests the presence of a universal scaling law. Sideview laser shadowgraphs depicting the subsurface motion in the water reveal the presence of a single stretched convective roll right beneath the leading edge of the spreading film. This fluid circulation, likely caused by evaporation and subsequent surface cooling of the rapidly spreading film, resembles a propagating Rayleigh–Bénard convective roll. We propose that this sublayer rotational flow provides the additional dissipation responsible for the reduced spreading exponent.
Keywords
This publication has 21 references indexed in Scilit:
- The leading edge of an oil slick, soap film, or bubble stagnant cap in Stokes flowJournal of Fluid Mechanics, 1992
- The spreading of oil on water in the surface-tension regimeJournal of Fluid Mechanics, 1987
- Flow beneath a stagnant film on water: the Reynolds ridgeJournal of Fluid Mechanics, 1982
- The spreading of thin liquid films on a water-air interfaceJournal of Fluid Mechanics, 1980
- The hydrodynamics of the spreading of one liquid on the surface of anotherJournal of Fluid Mechanics, 1978
- The Thoreau-Reynolds Ridge, a Lost and Found PhenomenonScience, 1971
- Surface Films Compacted by Moving Water: Demarcation Lines Reveal Film EdgesScience, 1970
- Factors affecting the use of monomolecular surface films to control oil pollution on waterEnvironmental Science & Technology, 1970
- Existence of a Surface Tension Discontinuity at a Liquid Free SurfaceNature, 1968
- On cellular convection driven by surface-tension gradients: effects of mean surface tension and surface viscosityJournal of Fluid Mechanics, 1964