Coalescence of Bubbles From Surface Forces As a Function of Gas Type and pH

Bubbles represent one of the simplest and most pervasive entities in the world around us. Despite their prevalence in nature and in numerous industrial processes, the behaviour of bubbles is still incompletely understood. This is mainly due to the difficulty in developing sufficiently accurate and reproducible experimental techniques for their examination. Here we report direct observations of controlled collisions between two micro-bubbles in water to elucidate the effect of gas type and solution pH on their stability against coalescence, using pure CO₂, air, nitrogen and argon. Bubble coalescence appears to be strongly linked to the presence of CO₂: whereas inert gases behave as predicted by charge repulsion from adsorbed ions, pure CO₂ bubbles are considerably more stable than predicted. Significantly, the trace concentration of CO₂ in air strongly biases its behaviour away from that of the inert gases. The stability of CO₂ bubbles cannot be explained by charge alone, suggesting an additional mechanism.

Reference

Tabor, RF, Chan, DYC, Grieser, F Dagastine, RR Angewandte Chemie 2011, 123, 3516-3518.