title: Wetting Transition of Condensed Droplets on Nanostructured Superhydrophobic Surfaces: Coordination of Surface Properties and Condensing Conditions.
abstract: Nanostructured superhydrophobic surfaces have been actively explored to promote favorable droplet dynamics for a wide range of technological applications. However, the tendency of condensed droplets to form as pinned states greatly limits their applicability in enhancing condensation heat transfer efficiency. Despite recent progresses, the understanding of physical mechanisms governing the wetting transition of condensed droplets is still lacking. In this work, a nanostructured superhydrophobic surface with tapered nanogaps is fabricated to demonstrate the coordination of surface wetting property, topography, and the condensing condition on the wetting state and dynamic behavior of condensed droplets. Combining the environmental scanning electron microscopy and optical visualization methods, we systematically show the morphology of nucleated droplets in nanostructures and the droplet dynamic evolution throughout the growth stages, which provides the direct evidence of condensing condition-induced droplet wetting transition. When the surface subcooling is smaller than 0.3 K, the droplets formed as the Cassie-Baxter state, followed by coalescence-induced droplet jumping. With the increase of surface subcooling up to 0.6 K, however, droplet formation occurs randomly inside nanogaps, resulting in the loss of superhydrophobicity. These new observations along with the new insights about the coordination of surface properties and condensing conditions on droplet wetting transition are useful for guiding the development of novel surfaces for improving droplet removal and phase-change heat transfer.
authors.affiliation: State Key Laboratory of Fine Chemicals & Liaoning Key Laboratory of Clean Utilization of Chemical Resources, Institute of Chemical Engineering, Dalian University of Technology , Dalian 116024, P. R. China.|Department of Mechanical Engineering, University of Colorado Boulder , Boulder, Colorado 80309-0427, United States.
authors.forename: Rongfu
authors.identifier: http://orcid.org/0000-0001-6499-7530
authors.initials: R
authors.lastname: Wen
authors.affiliation: State Key Laboratory of Fine Chemicals & Liaoning Key Laboratory of Clean Utilization of Chemical Resources, Institute of Chemical Engineering, Dalian University of Technology , Dalian 116024, P. R. China.
authors.forename: Zhong
authors.initials: Z
authors.lastname: Lan
authors.affiliation: State Key Laboratory of Fine Chemicals & Liaoning Key Laboratory of Clean Utilization of Chemical Resources, Institute of Chemical Engineering, Dalian University of Technology , Dalian 116024, P. R. China.
authors.forename: Benli
authors.initials: B
authors.lastname: Peng
authors.affiliation: State Key Laboratory of Fine Chemicals & Liaoning Key Laboratory of Clean Utilization of Chemical Resources, Institute of Chemical Engineering, Dalian University of Technology , Dalian 116024, P. R. China.
authors.forename: Wei
authors.initials: W
authors.lastname: Xu
authors.affiliation: Department of Mechanical Engineering, University of Colorado Boulder , Boulder, Colorado 80309-0427, United States.
authors.forename: Ronggui
authors.identifier: http://orcid.org/0000-0002-3602-6945
authors.initials: R
authors.lastname: Yang
authors.affiliation: State Key Laboratory of Fine Chemicals & Liaoning Key Laboratory of Clean Utilization of Chemical Resources, Institute of Chemical Engineering, Dalian University of Technology , Dalian 116024, P. R. China.
authors.forename: Xuehu
authors.initials: X
authors.lastname: Ma
keywords: condensing condition; droplet dynamics; nanostructured superhydrophobic surface; spatial confinement; synergistic coordination; wetting transition