title: Mechanism of supercooled droplet freezing on surfaces.
abstract: Understanding ice formation from supercooled water on surfaces is a problem of fundamental importance and general utility. Superhydrophobic surfaces promise to have remarkable 'icephobicity' and low ice adhesion. Here we show that their icephobicity can be rendered ineffective by simple changes in environmental conditions. Through experiments, nucleation theory and heat transfer physics, we establish that humidity and/or the flow of a surrounding gas can fundamentally switch the ice crystallization mechanism, drastically affecting surface icephobicity. Evaporative cooling of the supercooled liquid can engender ice crystallization by homogeneous nucleation at the droplet-free surface as opposed to the expected heterogeneous nucleation at the substrate. The related interplay between droplet roll-off and rapid crystallization is also studied. Overall, we bring a novel perspective to icing and icephobicity, unveiling the strong influence of environmental conditions in addition to the accepted effects of the surface conditions and hydrophobicity.
authors.affiliation: Laboratory of Thermodynamics in Emerging Technologies, Mechanical and Process Engineering Department, ETH Zurich, 8092 Zurich, Switzerland.
authors.forename: Stefan
authors.initials: S
authors.lastname: Jung
authors.forename: Manish K
authors.initials: MK
authors.lastname: Tiwari
authors.forename: N Vuong
authors.initials: NV
authors.lastname: Doan
authors.forename: Dimos
authors.initials: D
authors.lastname: Poulikakos
mesh_terms: D003460:Crystallization; D005615:Freezing; D005740:Gases; D006358:Hot Temperature; D057927:Hydrophobic and Hydrophilic Interactions; D007053:Ice; D008853:Microscopy / Q000379:methods; D018613:Microscopy, Confocal / Q000379:methods; D009584:Nitrogen / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D014783:Viscosity; D014867:Water / Q000737:chemistry
chemical_list: D005740:Gases; D007053:Ice; D014867:Water; D009584:Nitrogen