Abstract
Condensed liquid behavior on hydrophobic micro/nano-structured surfaces is a subject with multiple practical applications, but remains poorly understood. In particular, the loss of superhydrophobicity of hydrophobic micro/nanostructures during condensation, even when the same surface shows water-repellant characteristics when exposed to air, requires intensive investigation to improve and apply our understanding of the fundamental physics of condensation. Here, we postulate the criterion required for condensation to form from inside the surface structures by examining the grand potentials of a condensation system, including the properties of the condensed liquid and the conditions required for condensation. The results imply that the same hydrophobic micro/nano-structured surface could exhibit different liquid droplet behavior depending on the conditions. Our findings are supported by the observed phenomena: the initiation of a condensed droplet from inside a hydrophobic cavity, the apparent wetted state changes, and the presence of sticky condensed droplets on the hydrophobic micro/nano-structured surface.
Highlights
Condensed liquid behavior on hydrophobic micro/nano-structured surfaces is a subject with multiple practical applications, but remains poorly understood
We postulate the criterion required for condensation to form from inside the surface structures by examining the grand potentials of a condensation system, including the properties of the condensed liquid and the conditions required for condensation
The results imply that the same hydrophobic micro/nano-structured surface could exhibit different liquid droplet behavior depending on the conditions
Summary
Loss of superhydrophobicity of hydrophobic micro/nano structures during condensation. Our findings are supported by the observed phenomena: the initiation of a condensed droplet from inside a hydrophobic cavity, the apparent wetted state changes, and the presence of sticky condensed droplets on the hydrophobic micro/nano-structured surface. Our analysis of droplet formation from inside the hydrophobic nano-interstice is supported by changes in the observed apparent wetted state as the number of condensation nucleation sites are varied, and by the loss of superhydrophobicity on a hydrophobic micro/nanostructured (HMN) surface. Because the grown interface of the water droplet did not penetrate into the other hydrophobic cavities, the morphology of the condensed droplet maintained a near-perfect spherical shape except at the first initiation cavity From this observation, we supposed that the condensed liquid droplet had partial wetted states, consisting of the wetted part of the first nucleation cavity and the non-wetted part of the other cavities covered by the droplet as it increased in size. When the relative humidity is less than 1, the right-hand term of Eq (1) is positive
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