Superstability of Surface Nanobubbles

Abstract

Shock wave induced cavitation experiments and atomic force microscopy measurements of flat polyamide and hydrophobized silicon surfaces immersed in water are performed. It is shown that surface nanobubbles, present on these surfaces, do not act as nucleation sites for cavitation bubbles, in contrast to the expectation. This implies that surface nanobubbles are not just stable under ambient conditions but also under enormous reduction of the liquid pressure down to −6MPa. We denote this feature as superstability.

Effect of impurities in description of surface nanobubbles

“…However, for the Laplace pressure, even with significant fractional coverage the value remains much higher than the atmospheric pressure. This implies that the phenomenon of superstability of nanobubbles [12] could not be explained by the effect of soluble impurities alone; rather this effect could be looked upon as one of the possibly many factors that are simultaneously operative in ensuring the large stability of the nanobubbles. Lowering of surface tension (and the resulting changes of the nanobubble parameters) with a decrease of ω 0 can also be interpreted from a more physical perspective.…”

“…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. The different relevant issues pertaining to the formation and behavior of surface nanobubbles are well summarized in a very recent review by Hampton and Nguyen [17].…”

“…Investigations report nanobubbles to remain stable for over days when left undisturbed [12,15]. Simple calculations of the Laplace pressure (Δp) for a nanobubble of radius R b =100 nm (at the OTS-silicon-water interface, for example, with σ lg = 0.072N/m), however, gives an estimate of…”

Surface nanobubbles or Knudsen bubbles?

“…So the fact that surface nanobubbles [1][2][3][4][5][6][7][8][9][10] (typical height $20 nm and width $100 nm) persist for at least 11 orders of magnitude longer than this [11] is both remarkable and puzzling. Are classical diffusion laws simply not applicable at these length scales?…”

Activated drying in hydrophobic nanopores and the line tension of water

“…The formation of cavities able to bridge hydrophobic units provides a driving force for protein folding and supermolecular aggregation (9). Simulation examples of such drying-induced phenomena include the collapse of a polymer chain, multidomain proteins, and hydrophobic particles (9-13).Despite their direct observation, the easy formation and the high stability of nanobubbles on hydrophobic bodies still raise fundamental questions (5,14,15). Because of significant theoretical work, it is now established that, at the scale of the nanometer, macroscopic concepts apply: hydrophobicity is described by interfacial energies, and the drying transition in hydrophobic confinement is a first-order transition triggered by the nucleation of a critical vapor bubble (1).…”