Interfacial properties of Nano/Micro bubbles and their application to ultrasonic contrast agents

Abstract

A bubble is the entrapment of gas in a spherical shape inside liquids and it is related to many important physical and chemical processes. Many researchers have studied at the liquid-gas interface, which reflect many important properties of the gas and the adsorption of molecules at the microscopic level. The nucleation of a gas bubble is facilitated by the presence of dissolved gas, or of dust or ions. Surfactants also play a role in the nucleation by lowering the surface tension of aqueous solution, and the interface of bubbles can be characterized by the adsorptions, surface tensions and zeta-potentials. The adsorption of ionic substances onto an air/water surface can be found at some classical examples of ore flotation and foam separation processes and air bubbles are the target of research for ultrasonic contrast agents. Surfactant adsorption and ionization at the curved air/water interface investigated in a stable nanobubbles system generated by ultrasonication with palladium electrode. Nanobubbles are very useful to analyze the surface ionization of adsorbed monolayers at the bubble surface as well as determination of CMCs of ionic surfactant, since surface excess from the surface tension data at the planar air/water interface can be reasonably applied to calculate a degree of dissociation by assuming the planar air/water interface. Calculated degree of dissociation at the bubble surface is comparable with that of silica surface while it is very low compared with that of micelles. The zeta potential of nanobubbles generated by ultrasonication in the presence of palladium electrode was measured in aqueous pulmonary surfactants solutions. Equilibrium surface tension and dynamic surface tension were measured in comparison with other results. Nanobubble technique was used for study the adsorption behavior of DPPC/Cetyl alcohol/Tyloxapol. The retardation effect of Tyloxapol on the activation of DPPC surface activity at air/water interface was demonstrat...