title: Wetting of nanophases: Nanobubbles, nanodroplets and micropancakes on hydrophobic surfaces.
abstract: The observation by Atomic Force Microscopy of a range of nanophases on hydrophobic surfaces poses some challenging questions, not only related to the stability of these objects but also regarding their wetting properties. Spherical capped nanobubbles are observed to exhibit contact angles that far exceed the macroscopic contact angle measured for the same materials, whereas nanodroplets exhibit contact angles that are much the same as the macroscopic contact angle. Micropancakes are reported to consist of gas, in which case their wetting properties are mysterious. They should only be stable when the van der Waals forces act to thicken the film whereas for a gas, the van der Waals forces will always act to thin the film. Here we examine the available evidence and contribute some additional experiments in order to review our understanding of the wetting properties of these nanophases. We demonstrate that if in fact micropancakes consist of a contaminant their wetting properties can be explained, though the very high contact angles of nanobubbles remain unexplained.
authors.affiliation: Department of Applied Mathematics, Research School of Physical Sciences and Engineering, Australian National University, Canberra, ACT 0200, Australia.
authors.forename: Hongjie
authors.initials: H
authors.lastname: An
authors.affiliation: Hefei National Laboratory for Physical Sciences at the Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, PR China.
authors.forename: Guangming
authors.initials: G
authors.lastname: Liu
authors.affiliation: Department of Applied Mathematics, Research School of Physical Sciences and Engineering, Australian National University, Canberra, ACT 0200, Australia; Hefei National Laboratory for Physical Sciences at the Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, PR China. Electronic address: vince.craig@anu.edu.au.
authors.forename: Vincent S J
authors.initials: VS
authors.lastname: Craig
keywords: Contact angle; Line tension; Micropancakes; Nanobubbles; Nanodroplets