Do Liquid Films Rupture due to the So-Called Hydrophobic Force or Migration of Dissolved Gases?

Liquid films between hydrophobic (water-repellent) interfaces are not stable. The film rupture has been attributed to the so-called hydrophobic attraction. In this paper microinterferometry experiments show that gases inherently dissolved in water have a significant effect on the film rupture. Specifically, films of ultrapure deionized water in contact with degassed oil (squalene) were stable for as long as 35 min, while the water films in contact with nondegassed oil had a lifetime of seconds. These films ruptured at film thicknesses of similar to 150 nm. The degassed oil was also purposely left in contact with air. The oil-in-water emulsion films formed between degassed oil left in contact with air for a long period of time did not last longer than a few seconds and ruptured at significantly high thicknesses (about 800 nm). The degassing effect did not change the interfacial potential (about -65 mV) and the electrical double-layer repulsion between the squalene-water interfaces. Migration of dissolved gases between oil and water caused the rupture phenomena observed

Drainage, rupture, and lifetime of deionized water films: Effect of dissolved gases?

Gas bubbles coalesce in deionized (DI) water because the water (foam) films between the bubbles are not stable. The so-called hydrophobic attraction has been suggested as the cause of the film instability and the bubble coalescence. In this work, microinterferometry experiments show that foam films of ultrapure DI water can last up to 10s and the contact time between the two gas bubble surfaces at close proximity (similar to 1 mu m separation distance) significantly influences the film drainage, rupture, and lifetime. Specifically, when the two bubbles were first brought into contact, the films instantly ruptured at 0.5 mu m thickness. However, the film drainage rate and rupture thickness sharply decreased and the film lifetime steeply increased with increasing contact time up to 10 min, but then they leveled off. The constant thickness of film rupture was around 35 nm. Possible contamination was vigorously investigated and ruled out. It is argued that migration of gases inherently dissolved in water might cause the transient behavior of the water films at the short contact time. The film drainage rate and instability at the long contact time were analyzed employing Eriksson et al.'s phenomenological theory of long-range hydrophobic attraction (Eriksson, J.C.; Ljunggren, S.; Claesson, P.M., J. Chem. Soc., Faraday Trans. 2 1989, 85, 163-176) and the hypothesis of water molecular structure modified by dissolved gases, and the extended Stefan-Reynolds theory by incorporating the mobility of the air-DI-water interfaces