title: On the shedding of impaled droplets: The role of transient intervening layers.
abstract: Maintaining the non-wetting property of textured hydrophobic surfaces is directly related to the preservation of an intervening fluid layer (gaseous or immiscible liquid) between the droplet and substrate; once displaced, it cannot be recovered spontaneously as the fully penetrated Wenzel wetting state is energetically favorable. Here, we identify pathways for the "lifting" of droplets from the surface texture, enabling a complete Wenzel-to-Cassie-Baxter wetting state transition. This is accomplished by the hemiwicking of a transient (limited lifetime due to evaporation) low surface tension (LST) liquid, which is capable of self-assembling as an intervening underlayer, lifting the droplet from its impaled state and facilitating a skating-like behavior. In the skating phase, a critical substrate tilting angle is identified, up to which underlayer and droplet remain coupled exhibiting a pseudo-Cassie-Baxter state. For greater titling angles, the droplet, driven by inertia, detaches itself from the liquid intervening layer and transitions to a traditional Cassie-Baxter wetting state, thereby accelerating and leaving the underlayer behind. A model is also presented that elucidates the mechanism of mobility recovery. Ultimately, this work provides a better understanding of multiphase mass transfer of immiscible LST liquid-water mixtures with respect to establishing facile methods towards retaining intervening layers.
authors.affiliation: Laboratory of Thermodynamics in Emerging Technologies, Mechanical and Process Engineering Department, ETH Zürich, 8092 Zurich, Switzerland.
authors.forename: Christos
authors.initials: C
authors.lastname: Stamatopoulos
authors.affiliation: Laboratory of Thermodynamics in Emerging Technologies, Mechanical and Process Engineering Department, ETH Zürich, 8092 Zurich, Switzerland.
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Schutzius
authors.affiliation: Laboratory of Thermodynamics in Emerging Technologies, Mechanical and Process Engineering Department, ETH Zürich, 8092 Zurich, Switzerland.
authors.forename: Christian J
authors.initials: CJ
authors.lastname: Köppl
authors.affiliation: Laboratory of Thermodynamics in Emerging Technologies, Mechanical and Process Engineering Department, ETH Zürich, 8092 Zurich, Switzerland.
authors.forename: Nicolas
authors.initials: N
authors.lastname: El Hayek
authors.affiliation: Laboratory of Thermodynamics in Emerging Technologies, Mechanical and Process Engineering Department, ETH Zürich, 8092 Zurich, Switzerland.
authors.forename: Tanmoy
authors.initials: T
authors.lastname: Maitra
authors.affiliation: ABB Switzerland, Corporate Reasearch, 5405 Baden-Daetwill, Switzerland.
authors.forename: Jaroslav
authors.initials: J
authors.lastname: Hemrle
authors.affiliation: Laboratory of Thermodynamics in Emerging Technologies, Mechanical and Process Engineering Department, ETH Zürich, 8092 Zurich, Switzerland.
authors.forename: Dimos
authors.initials: D
authors.lastname: Poulikakos