Retraction of a fluid from a surface it was forced to cover
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In fluid mechanics, dewetting is one of the processes that can occur at a solid–liquid, solid–solid[1] or liquid–liquid interface. Generally, dewetting describes the process of retraction of a fluid from a non-wettable surface it was forced to cover. The opposite process—spreading of a liquid on a substrate—is called wetting. The factor determining the spontaneous spreading and dewetting for a drop of liquid placed on a solid substrate with ambient gas, is the so-called spreading coefficient S:
Surface tension diagram of a liquid droplet on a solid substrate. The surface of the liquid has the shape of a spherical cap, due to Laplace pressure
where γSG is the solid-gas surface tension, γSL is the solid-liquid surface tension and γLG is the liquid-gas surface tension (measured for the mediums before they are brought in contact with each other).
When S > 0, the spontaneous spreading occurs, and if S < 0, partial wetting is observed, meaning the liquid will only cover the substrate to some extent.[2]
The equilibrium contact angle is determined from the Young–Laplace equation.
Spreading and dewetting are important processes for many applications, including adhesion, lubrication, painting, printing, and protective coating. For most applications, dewetting is an unwanted process, because it destroys the applied liquid film.
Dewetting can be inhibited or prevented by photocrosslinking the thin film prior to annealing, or by incorporating nanoparticle additives into the film.[3]
Surfactants can have a significant effect on the spreading coefficient. When a surfactant is added, its amphiphilic properties cause it to be more energetically favorable to migrate to the surface, decreasing the interfacial tension and thus increasing the spreading coefficient (i.e. making S more positive). As more surfactant molecules are absorbed into the interface, the free energy of the system decreases in tandem to the surface tension decreasing, eventually causing the system to become completely wetting.
In biology, by analogy with the physics of liquid dewetting, the process of tunnel formation through endothelial cells has been referred to as cellular dewetting.
^Leroy, F.; Borowik, Ł.; Cheynis, F.; Almadori, Y.; Curiotto, S.; Trautmann, M.; Barbé, J.C.; Müller, P. (2016). "How to control solid state dewetting : A short review". Surface Science Reports. 71 (2): 391. Bibcode:2016SurSR..71..391L. doi:10.1016/j.surfrep.2016.03.002.
^Rosen, Milton J. (2004). Surfactants and Interfacial Phenomena (3rd ed.). Hoboken, New Jersey: Wiley-Interscience. p. 244. ISBN 978-0-471-47818-8. OCLC 475305499.
^Carroll, Gregory T.; Turro, Nicholas J.; Koberstein, Jeffrey T. (2010) Patterning Dewetting in Thin Polymer Films by Spatially Directed Photocrosslinking Journal of Colloid and Interface Science, Vol. 351, pp 556-560 doi:10.1016/j.jcis.2010.07.070
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252–266. doi:10.5465/amr.2008.27752775. ISSN 0363-7425. Devers, Cynthia E.; Dewett, Todd; Mishina, Yuri; Belsito, Carrie A. (20 August 2008). "A General Theory...
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Whitesides, George M. (1 October 2003). "Asymmetric Dimers Can Be Formed by Dewetting Half-Shells of Gold Deposited on the Surfaces of Spherical Oxide Colloids"...
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