Effects of Dissolved Gas on the Hydrophobic Attraction between Surfactant-Coated Surfaces

Abstract

The effect of dissolved gas on the hydrophobic attraction between double-chained surfactant monolayers physisorbed on mica has been studied using a surface forces apparatus (SFA). Distance vs time data were obtained over the full distance regime from D approximately 1000 A down to contact using the dynamic SFA method. Removal of dissolved gas was seen to reduce the range of the attraction while the short-range attraction (under approximately 250 A) remained unchanged. The implications for the possibility of two distinct force regimes in the interactions between hydrophobic surfaces are discussed.

Reduced water density at hydrophobic surfaces: Effect of dissolved gases

“…These measurements elucidate the experimental observations of a reduced hydrophobic attraction in deaerated water (20,(27)(28)(29)(30) if this interaction is due to the nucleation of vapor bridges forming between two hydrophobic surfaces once they are sufficiently close to each other. The statistical nature of the nucleation process (25,39,40), depending as it would on the time the surfaces remain at a given separation, could make it difficult to express this interaction in terms of an equilibrium potential function, which could be the reason why experiments such as surface forces apparatus, AFM, and colloidal stability studies, Fig.…”

“…There is evidence of preexisting bubbles 50-500 nm in diameter and 5-50 nm in height on some hydrophobic surfaces (mechanism iii), but these bubbles have only been detected by invasive techniques such as atomic force microscopy (AFM) imaging (10,(14)(15)(16)(17). Other AFM and surface forces apparatus studies have not reported seeing nanobubbles (19,20).…”

“…These concerns, and other issues outlined by Ball (9), have precluded accurate measurement of the extent of the depletion zone. Most importantly, these studies did not explore the effects of dissolved air or other gases, which have been heavily implicated in the hydrophobic interaction (20,(27)(28)(29)(30).…”

“…Continuous stirring was used to shake off the bubbles nucleated on the Teflon chips. The system was under vacuum for Ϸ1 h until no bubble formation was seen on the Teflon chips (20). Before each NR measurement, the OTS surfaces were cleaned with deionized water, chloroform, and ethanol, followed by drying in ultra-high-purity Ar.…”

Force measurements with the atomic force microscope: Technique, interpretation and applications

“…Dissolved air and other gases seem to influence the long-range component of the hydrophobic force. In deaerated water, i.e., water in which dissolved gases have been taken out as much as possible, the formation of nanobubbles is very much reduced, and the force is of shorter range [507,511,514,537,539,540]. Nanobubbles on hydrophobic surface could be imaged with the AFM in tapping mode [541][542][543][544][545] (Fig.…”