Change in size and number of sodium laurate microbubbles with time in saline at different air concentrations

The study of the annihilation mechanisms of microbubbles is a very important topic in the development of ultrasound contrast agents. To gain better insight into the annihilation mechanisms, knowledge of the change in the number and size of microbubbles with time in saline is necessary. In this study, the use of a Coulter Multisizer is proposed, and the change in number and size of microbubbles is accurately measured. As a result, mechanisms for longevity and annihilation are suggested. Sodium laurate is used for the coating layer of the microbubbles. The measured longevity of sodium laurate microbubbles is compared with the results of a simulation of free air microbubbles. Although the coating layers lower the diffusion rate of air from microbubbles, diffusion still occurs. The diffusion of air contributes to the size of the microbubbles and the dissolution of the surfactant coating layer causes a decrease in the number of microbubbles. The reasons for these assertions are discussed in this paper. When the concentration of dissolved air in saline is close to saturation, the annihilation mechanism of sodium laurate microbubbles changes to the dissolution of the coating layer into the solution. In addition, it is proposed from the experimental results that small particles less than 10 μm in size which dissolve slowly in saline are formed after the shrinking of microbubbles by diffusion.