title: Morphology of air nanobubbles trapped at hydrophobic nanopatterned surfaces.
abstract: The details of air nanobubble trapping at the interface between water and a nanostructured hydrophobic silicon surface are investigated using X-ray scattering and contact angle measurements. Large-area silicon surfaces containing hexagonally packed, 20 nm wide hydrophobic cavities provide ideal model surfaces for studying the morphology of air nanobubbles trapped inside cavities and its dependence on the cavity depth. Transmission small-angle X-ray scattering measurements show stable trapping of air inside the cavities with a partial water penetration of 5-10 nm into the pores, independent of their large depth variation. This behavior is explained by consideration of capillary effects and the cavity geometry. For parabolic cavities, the liquid can reach a thermodynamically stable configuration-a nearly planar nanobubble meniscus-by partially penetrating into the pores. This microscopic information correlates very well with the macroscopic surface wetting behavior.
authors.affiliation: Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA. checco@bnl.gov
authors.forename: Antonio
authors.initials: A
authors.lastname: Checco
authors.forename: Tommy
authors.initials: T
authors.lastname: Hofmann
authors.forename: Elaine
authors.initials: E
authors.lastname: DiMasi
authors.forename: Charles T
authors.initials: CT
authors.lastname: Black
authors.forename: Benjamin M
authors.initials: BM
authors.lastname: Ocko
mesh_terms: D000388:Air; D057927:Hydrophobic and Hydrophilic Interactions; D049329:Nanostructures / Q000737:chemistry*; D036103:Nanotechnology / Q000379:methods; D010316:Particle Size; D012825:Silicon / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D012825:Silicon