Effect of Nonionic Surfactants on Na* Emission during Sonoluminescence of Aqueous NaCl Solutions

Abstract

Atomic emission of sodium during multibubble sonoluminescence of NaCl aqueous solutions is studied under the addition of nonionic (ethoxylated tridecyl alcohol with degree of ethoxylation of 10; ethoxylated tetradecyl alcohol with degree of ethoxylation of 15), anionic (sodium dodecyl sulfate), and cationic (dodecyl trimethylammonium bromide) surfactants. It is shown that as the concentration of NaCl increases, 0.5 mM of a surfactant of any type in the solution results in a faster increase in Na* emission, compared to a pure salt solution. The effect weakens in the order anionic–nonionic–cationic surfactant. An increase in the concentration of nonionic surfactants in a solution of 10 mM NaCl also results in an increase in Na* emission. It is found that adding 10 mM LiCl and 10 mM ZnSO4 to a solution of a mixture of 10 mM NaCl and 0.5 mM of a nonionic surfactant has no effect on the intensity of Na* emission. It is concluded that in solutions with surface-active properties, bubble–solution boundary layer is likely zone of Na* emission, and the presence of surfactants increases the concentration of Na+ ions in the boundary layer. For ionic surfactants, the effect is accompanied by electrostatic interaction between Na+ and the charged surface of a bubble.