Images of Nanobubbles on Hydrophobic Surfaces and Their Interactions

Abstract

Imaging of hydrophobic surfaces in water with tapping mode atomic force microscopy reveals them to be covered with soft domains, apparently nanobubbles, that are close packed and irregular in cross section, have a radius of curvature of the order of 100 nm, and a height above the substrate of 20-30 nm. Complementary force measurements show features seen in previous measurements of the long-range hydrophobic attraction, including a jump into a soft contact and a prejump repulsion. The distance of the jump is correlated with the height of the images. The morphology of the nanobubbles and the time scale for their formation suggest the origin of their stability.

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

“…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. 23).…”

Nanobubbles in Solid-State Nanopores

“…Nanobubbles have been observed in both atomic force microscopy [12,13] and fast freezing experiments [14]. The origin of their thermodynamic stability is still under debate [15].…”

Effect of impurities in description of surface nanobubbles

“…On the contrary, the typical time scale that can be ascribed to the formation or morphological changes (if any) of the surface nanobubbles is at least of the order of 10 minutes [5,34,35]. Hence, except for the initial transients that last for very small time, the surface nanobubbles are expected to be formed in presence of the constant reduced value of the air-water surface tension, thereby allowing us to invoke equilibrium treatment.…”

“…The presence of the hydrophobic surface leads to the formation of spherical cap-like bubbles at the solid-liquid interface, called "surface nanobubbles". Over the years AFM techniques have been the most popular method in studying these surface nanobubbles [1][2][3][4][5]. Depending on the conditions that lead to their formation, different behaviors of the nanobubbles have been found by these studies: e.g., their spherical cap-like shape and chances of deviation from that shape [6][7][8], merging of two adjacently located nanobubbles [6,9], disappearance of nanobubbles in case the water is degassed [10], possible reappearances by exchange of solvents [7,[11][12][13][14][15] or increase of temperature [11], or electrolysis [9,16] etc.…”