Rupture of Wetting Films Caused by Nanobubbles
- 26 November 2003
- journal article
- Published by American Chemical Society (ACS) in Langmuir
- Vol. 20 (1), 164-168
- https://doi.org/10.1021/la0354887
Abstract
It is now widely accepted that nanometer sized bubbles, attached at a hydrophobic silica surface, can cause rupture of aqueous wetting films due to the so-called nucleation mechanism. But the knowledge of the existence of such nanobubbles does not give an answer to how the subprocesses of this rupture mechanism operate. The aim of this paper is to describe the steps of the rupture process in detail: (1) During drainage of the wetting film, the apex of the largest nanobubble comes to a distance from the wetting film surface, where surface forces are acting. (2) An aqueous “foam film” in nanoscale size is formed between the bubble and the wetting film surface; in this foam film different Derjaguin−Landau−Verwey−Overbeek (DLVO) forces are acting than in the surrounding wetting film. In the investigated system, hydrophobized silica/water/air, all DLVO forces in the wetting film are repulsive, whereas in the foam film the van der Waals force becomes attractive. (3) The surface forces over and around the apex of the nanobubble lead to a deformation of the film surfaces, which causes an additional capillary pressure in the foam film. An analysis of the pressure balance in the system shows that this additional capillary pressure can destabilize the foam film and leads to rupture of the foam film. (4) If the newly formed hole in the wetting film has a sufficient diameter, the whole wetting film is destabilized and the solid becomes dewetted. Experimental data of rupture thickness and lifetime of wetting films of pure electrolyte and surfactant solutions show that the stabilization of the foam film by surfactants has a crucial effect on the stability of the wetting film.Keywords
This publication has 6 references indexed in Scilit:
- Optical Observation of Gas Bridging between Hydrophobic Surfaces in WaterJournal of Colloid and Interface Science, 2002
- The influence of acting forces on the rupture mechanism of wetting films — nucleation or capillary wavesColloids and Surfaces A: Physicochemical and Engineering Aspects, 2001
- Images of Nanobubbles on Hydrophobic Surfaces and Their InteractionsPhysical Review Letters, 2001
- The hydrophobic force in flotation-a critiqueColloids and Surfaces A: Physicochemical and Engineering Aspects, 2001
- The influence of dissolved gas on the interactions between surfaces of different hydrophobicity in aqueous media Part I. Measurement of interaction forcesPhysical Chemistry Chemical Physics, 1999
- Energetic criteria for the breakup of liquid films on nonwetting solid surfacesJournal of Colloid and Interface Science, 1990