Collective behavior of bulk nanobubbles produced by the alternating polarity electrolysis

TL;DR

This paper demonstrates a controlled method for producing and analyzing bulk nanobubbles in liquids using alternating polarity electrolysis, revealing their structure, size, and stability over time.

Contribution

It introduces a novel electrolysis technique to generate and control nanobubbles, with detailed visualization and size analysis, advancing nanobubble production methods.

Findings

Nanobubbles have a concentration of 2x10^18 m^-3 in the enriched volume.

Average nanobubble size during production is 60-80 nm.

Nanobubbles grow to about 250 nm 15 minutes after production stops.

Abstract

Nanobubbles in liquids are mysterious gaseous objects having exceptional stability. They promise a wide range of applications but their production is not well controlled and localized. Alternating polarity electrolysis of water is a tool that can control production of bulk nanobubbles in space and time without generating larger bubbles. Using the schlieren technique a detailed three-dimensional structure of a dense cloud of nanobubbles above the electrodes is visualized. It is demonstrated that the thermal effects produce different schlieren pattern and have different dynamics. A localized volume enriched with nanobubbles can be separated from the parent cloud and exists on its own. This volume demonstrates buoyancy from which the concentration of nanobubbles is estimated as 2x10^18 m^-3. This concentration is smaller than that in the parent cloud. Dynamic light scattering shows that the average size of nanobubbles during the process is 60-80 nm. The bubbles are observed 15 minutes after switching off the electrical pulses but their size is shifted to larger values of about 250 nm. Thus, an efficient way to generate and control nanobubbles is proposed.