Existence of charged submicrobubble clusters in polar liquids as revealed by correlation between optical cavitation and electrical conductivity

It has been shown previously that in aqueous systems there exist charged gas-filled submicrobubbles (bubstons) associated in clusters that serve as nuclei for optical cavitation [N.F. Bunkin, A.V. Lobeyev, B.W. Ninham and O.I. Vinogradova, Langmuir, submitted]. Here optical cavitation as a function of temperature for a binary solution (with upper critical point) of polar liquids has been explored. For temperatures above the binodal the cavitation probability is enhanced, and the formation of a macroscopic bubble during the laser pulse is most likely due to coalescence of submicrobubble clusters. For temperatures below the binodal, the appearance of new phase droplets leads to a drastic decrease in the cavitation probability. The effect is not associated with changes in concentration of the dissolved gas or to influence of solvophobicity degree of the walls. The inhibited cavitation appears to be closely connected with the decrease in the concentration of ions that has been confirmed by simultaneous decrease in the electrical conductivity of the system. It has been shown that the results obtained constitute indirect evidence for the existence in polar liquids of clusters formed just by charged submicrobubbles, or bubstons.