Edited by Pablo G. Debenedetti, Princeton University, Princeton, NJ, and approved September 24, 2019 (received for review August 8, 2019)
Whether a drop of liquid such as water is repelled from a solid substrate yielding a large angle of intersection θ between the drop’s surface and the substrate or is strongly attracted, small θ, is key to the function of a host of physical and biological systems. We elucidate the physics of hydrophobic and hydrophilic substrates in terms of wetting and drying surface phase diagrams. These display a surprising variety of forms that depend upon the nature of the substrate–liquid and liquid–liquid attractive forces. Liquids near weakly attractive substrates exhibit critical drying, a phenomenon occurring as
Clarifying the factors that control the contact angle of a liquid on a solid substrate is a long-standing scientific problem pertinent across physics, chemistry, and materials science. Progress has been hampered by the lack of a comprehensive and unified understanding of the physics of wetting and drying phase transitions. Using various theoretical and simulational techniques applied to realistic fluid models, we elucidate how the character of these transitions depends sensitively on both the range of fluid–fluid and substrate–fluid interactions and the temperature. Our calculations uncover previously unrecognized classes of surface phase diagram which differ from that established for simple lattice models and often assumed to be universal. The differences relate both to the topology of the phase diagram and to the nature of the transitions, with a remarkable feature being a difference between drying and wetting transitions which persists even in the approach to the bulk critical point. Most experimental and simulational studies of liquids at a substrate belong to one of these previously unrecognized classes. We predict that while there appears to be nothing particularly special about water with regard to its wetting and drying behavior, superhydrophobic behavior should be more readily observable in experiments conducted at high temperatures than at room temperature.
Author contributions: R.E. and N.B.W. designed research; R.E., M.C.S., and N.B.W. performed research; and R.E. and N.B.W. wrote the paper.
The authors declare no competing interest.
This article is a PNAS Direct Submission.
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This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1913587116/-/DCSupplemental.
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