The collapse transition on superhydrophobic surfaces

Abstract

We investigate the transition between the Cassie-Baxter and Wenzel states of a slowly evaporating, micron-scale drop on a superhydrophobic surface. In two dimensions analytical results show that there are two collapse mechanisms. For long posts the drop collapses when it is able to overcome the free energy barrier presented by the hydrophobic posts. For short posts, as the drop loses volume, its curvature increases allowing it to touch the surface below the posts. We emphasise the importance of the contact line retreating across the surface as the drop becomes smaller: this often preempts the collapse. In a quasi-three dimensional simulation we find similar behaviour, with the additional feature that the drop can de-pin from all but the peripheral posts, so that its base resembles an inverted bowl.

6 pages, 7 figures

References in corpus (5)

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• Modelling contact angle hysteresis on chemically patterned and superhydrophobic surfaces
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• Contact angle determination in multicomponent lattice Boltzmann simulations
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• The contact line behaviour of solid-liquid-gas diffuse-interface models
• Impalement transitions in droplets impacting microstructured superhydrophobic surfaces
• Mechanism of the Cassie-Wenzel transition via the atomistic and continuum string methods
• Superhydrophobicity on hairy surfaces
• Anisotropic hysteresis on ratcheted superhydrophobic surfaces
• Fall and rise of small droplets on rough hydrophobic substrates
• Surveying the Free Energy Landscapes of Continuum Models: Application to Soft Matter Systems
• Intrusion and extrusion of a liquid on nanostructured surfaces
• The Impact of Surface Geometry, Cavitation, and Condensation on Wetting Transitions: Posts and Reentrant Structures
• The surface tension of Martini 3 water mixtures