The influence of storage conditions and container materials on the long term stability of bulk nanobubbles - Consideration from a perspective of interactions between bubbles and surroundings

The stability of nanobubbles (NBs), also known as ultrafine bubbles (UFBs), in bulk liquid was investigated experimentally. Temporal variations in the properties of NB dispersions stored in a virtually airtight glass bottle, without any gas-liquid interface, at a constant temperature were measured periodically with a nanoparticle tracking analyzer. The NB number concentration slowly diminished with time over 9 months but measurements suggested that gas-filled bubbles indeed remained. Immersing different polymer materials in NB dispersions exerted differing influences on NB number concentrations by hydrophobic interaction between the NBs and those materials. A NB dispersion stored in a polyethylene (PE) pouch showed a more rapid decay of the number concentration compared to samples stored in a glass bottle. The adsorption of NBs to the inner wall of the PE pouch and subsequent gas transfer through the pouch wall to the atmosphere was inferred to be the predominant mechanism of NB decay. Key words: bulk nanobubbles, ultrafine bubbles, hydrophobic interaction, stability, lengthy storage. (C) 2020 Elsevier Ltd. All rights reserved.