Authors Stöckelhuber, K.W. ; Radoev, B. ; Wenger, A. ; Schulze, H.J.
Title Rupture of Wetting Films Caused by Nanobubbles
Date 31.12.2004
Number 11675
Abstract It is now widely accepted that nanometer sized bubbles, attached at a hydrophobic silica surface, cancause rupture of aqueous wetting films due to the so-called nucleation mechanism. But the knowledge ofthe existence of such nanobubbles does not give an answer to how the subprocesses of this rupture mechanismoperate. The aim of this paper is to describe the steps of the rupture process in detail: (1) During drainageof 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 bubbleand 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 Waalsforce becomes attractive. (3) The surface forces over and around the apex of the nanobubble lead to adeformation of the film surfaces, which causes an additional capillary pressure in the foam film. Ananalysis of the pressure balance in the system shows that this additional capillary pressure can destabilizethe foam film and leads to rupture of the foam film. (4) If the newly formed hole in the wetting film hasa sufficient diameter, the whole wetting film is destabilized and the solid becomes dewetted. Experimentaldata of rupture thickness and lifetime of wetting films of pure <br />electrolyte and surfactant solutions showthat the stabilization of the foam film by surfactants has a crucial effect on the stability of the wettingfilm.
Publisher Langmuir
Citation Langmuir 20 (2004) 164-168

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