Nucleation threshold and deactivation mechanisms of nanoscopic cavitation nuclei

TL;DR

This study experimentally verifies the theoretical nucleation threshold for nanoscopic cavitation nuclei and explores their deactivation mechanisms, revealing gas diffusion, bubble collapse, and superhydrophobic properties affecting cavitation activity.

Contribution

It provides the first experimental validation of crevice theory predictions for nanoscopic cavities and uncovers mechanisms behind cavitation deactivation and superhydrophobic nuclei behavior.

Findings

Experimental thresholds match theoretical predictions.

Gas diffusion and bubble collapse deactivate cavitation nuclei.

Superhydrophobic nuclei resist deactivation unless impacted by high-speed jets.

Abstract

The acoustic nucleation threshold for bubbles trapped in cavities has theoretically been predicted within the crevice theory by Atchley & Prosperetti [J. Acoust. Soc. Am. 86, 1065-1084 (1989)]. Here, we determine this threshold experimentally, by applying a single pressure pulse to bubbles trapped in cylindrical nanoscopic pits ("artificial crevices") with radii down to 50 nm. By decreasing the minimum pressure stepwise, we observe the threshold for which the bubbles start to nucleate. The experimental results are quantitatively in excellent agreement with the theoretical predictions of Atchley & Prosperetti. In addition, we provide the mechanism which explains the deactivation of cavitation nuclei: gas diffusion together with an aspherical bubble collapse. Finally, we present superhydrophobic nuclei which cannot be deactivated, unless with a high-speed liquid jet directed into the pit.