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Published July 1, 1998 | public
Journal Article Open

Fluorescence visualization of a convective instability which modulates the spreading of volatile surface films


The spontaneous spreading of a thin liquid film along the surface of a deep liquid layer of higher surface tension is a ubiquitous process which provides rapid and efficient surface transport of organic or biological material. For a source of constant concentration, the leading edge of a nonvolatile, immiscible film driven to spread by gradients in surface tension is known to advance as t^3/4 in time. Recent experiments using laser shadowgraphy to detect the advancing front of spreading films indicate, however, that immiscible but volatile sources of constant concentration spread with a reduced exponent according to t^1/2. Using a novel technique whereby fluorescent lines are inscribed in water, we have detected the evolution of a thermal instability beneath the leading edge of volatile films which strongly resembles a Rayleigh-Bénard roll. We propose that the increased dissipation from this rotational flow structure is likely responsible for the reduction in spreading exponent. This observation suggests a conceptual framework for coupling the effects of evaporation to the dynamics of spreading.

Additional Information

©1998 American Institute of Physics. (Received 17 October 1997; accepted 16 March 1998) The authors would like to thank Dr. W. R. Lempert and Professor R. B. Miles for allowing us access to the flow tagging apparatus. S.M.T. gratefully acknowledges support from the NSF through its RIA and CAREER programs as well as a seed grant distributed through the Princeton Materials Institute. The Exxon Education Foundation and the Can Manufacturer's Institute also provided funding for this work.


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