title: Variation of Local Surface Properties of an Air Bubble in Water Caused by Its Interaction with Another Surface.
abstract: Surface and hydrodynamic forces acting between an air bubble and a flat mica surface in surfactant-free water and in 1 mM KCl solution have been investigated by observing film drainage using a modified surface force apparatus (SFA). The bubble shapes observed with the SFA are compared to theoretical profiles computed from a model that considers hydrodynamic interactions, surface curvature, and disjoining pressure arising from electrical double layer and van der Waals interactions. It is shown that the bubble experiences double-layer forces, and a final equilibrium wetting film between the bubble and mica surfaces is formed by van der Waals repulsion. However, comparison with the theoretical model reveals that the double-layer forces are not simply a function of surface separation. Rather, they appear to be changed by one of more of the following: the bubble's dynamic deformation, its proximity to another surface, and/or hydrodynamic flow in the aqueous film that separate them. The same comments apply to the hydrodynamic mobility or immobility of the air-water interface. Together the results show that the bubble's surface is "soft" in two senses: in addition to its well-known deformability, its local properties are affected by weak external forces, in this case the electrical double-layer interactions with a nearby surface and hydrodynamic flow in the neighboring aqueous phase.
authors.forename: Lorena A
authors.initials: LA
authors.lastname: Del Castillo
authors.forename: Satomi
authors.initials: S
authors.lastname: Ohnishi
authors.affiliation: School of Mathematics and Statistics, University of Melbourne , Parkville, Victoria 3010, Australia.
authors.forename: Steven L
authors.initials: SL
authors.lastname: Carnie
authors.affiliation: Institute for Frontier Materials, Deakin University , 221 Burwood Highway, Burwood, Victoria 3125, Australia.
authors.forename: Roger G
authors.initials: RG
authors.lastname: Horn