Stöckelhuber Klaus Werner, Radoev Boryan, Wenger Andreas, Schulzet Hans Joachim
Max-Planck-Research Group for Colloids and Surfaces at the Institute of Ceramics, Glass and Construction Materials at the TU Bergakademie Freiberg, Chemnitzer Strasse 40, D-09599 Freiberg, Germany.
Langmuir. 2004 Jan 6;20(1):164-8. doi: 10.1021/la0354887.
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.
现在人们普遍认为，附着在疏水二氧化硅表面的纳米气泡会由于所谓的成核机制导致水润湿膜破裂。但是，关于此类纳米气泡的存在的知识并不能回答这种破裂机制的子过程是如何运作的。本文的目的是详细描述破裂过程的各个步骤：（1）在润湿膜排水过程中，最大纳米气泡的顶点与润湿膜表面的距离达到表面力起作用的位置。（2）在气泡和润湿膜表面之间形成了纳米级尺寸的水“泡沫膜”；在这个泡沫膜中，与周围的润湿膜相比，作用着不同的德贾金 - 朗道 - 韦弗 - 奥弗贝克（DLVO）力。在所研究的疏水二氧化硅/水/空气系统中，润湿膜中的所有DLVO力都是排斥力，而在泡沫膜中范德华力变为吸引力。（3）纳米气泡顶点上方和周围的表面力导致膜表面变形，这在泡沫膜中引起额外的毛细管压力。对系统压力平衡的分析表明，这种额外的毛细管压力会使泡沫膜不稳定并导致泡沫膜破裂。（4）如果在润湿膜中新形成的孔具有足够的直径，整个润湿膜就会不稳定，固体就会去湿。纯电解质和表面活性剂溶液的润湿膜破裂厚度和寿命的实验数据表明，表面活性剂对泡沫膜的稳定作用对润湿膜的稳定性有至关重要的影响。
