title: Proton transfer between organic acids and bases at the acoustic bubble-aqueous solution interface.
abstract: The multibubble sonoluminescence (MBSL) emission intensity from aqueous solutions containing simple aliphatic organic acids (RCOOH) and bases (RNH2) and mixtures of the two types of solutes has been examined as a function of pH. In solutions containing either an organic acid or base, under pH conditions where the solutes are predominately in their ionized form (i.e., RCOO- and RNH3+), the MBSL intensity is identical with that obtained in pure water. Alternatively, under pH conditions where the solutes are in their un-ionized form the MBSL intensity is suppressed. However, in solute mixtures of RCOO- and RNH3+ in the pH range of 7 to 9, the MBSL intensity was significantly suppressed relative to that from water. To explain the results of the mixed solute system it has been postulated that when the bubble/solution interface experiences the extreme temperature conditions that accompany bubble collapse, proton transfer occurs between acid-base ion-pair complexes, [RCOO-...RNH3+], adsorbed at the bubble/solution interface. The neutral forms of the solutes then evaporate into the bubble during its expansion phase and through a complex series of events, over a number of bubble oscillations, reduce the core temperature of the collapsing bubble and hence the SL intensity.
authors.affiliation: Particulate Fluids Processing Centre, School of Chemistry, University of Melbourne, VIC 3010, Australia.
authors.forename: Muthupandian
authors.initials: M
authors.lastname: Ashokkumar
authors.forename: Franz
authors.initials: F
authors.lastname: Grieser