Preferred sizes and ordering in surface nanobubble populations

TL;DR

This study statistically analyzes two types of surface nanobubble populations, revealing preferred sizes and spatial arrangements that suggest structured formation processes, with differences between the two creation methods.

Contribution

It introduces a detailed statistical characterization of nanobubble size and spatial distributions, highlighting structuring effects not explained by random packing models.

Findings

Type A bubbles have a preferred radius of 20 nm.

Type A bubbles show a preferred spacing at ~5.5 times the radius.

Type B bubbles exhibit two distinct size distributions.

Abstract

Two types of homogeneous surface nanobubble populations, created by different means, are analyzed statistically on both their sizes and spatial positions. In the first type (created by droplet-deposition, case A) the bubble size R is found to be distributed according to a generalized gamma law with a preferred radius R*=20 nm. The radial distribution function shows a preferred spacing at ~5.5 R*. These characteristics do not show up in comparable Monte-Carlo simulations of random packings of hard disks with the same size distribution and the same density, suggesting a structuring effect in the nanobubble formation process. The nanobubble size distribution of the second population type (created by ethanol-water exchange, case B) is a mixture of two clearly separated distributions, hence, with two preferred radii. The local ordering is less significant, due to the looser packing of the nanobubbles.