Crucial Role of Surfactants in Bubble-Propelled Microengines

Bubble-propelled autonomous microengines are expected to perform various tasks in related biomedical and environmental fields. The presence of surfactant in the environment is necessary for movement of microjets because it lowers interfacial tension required for detachment of the bubble from the microjet engine. We study the dependence of the mobility of microjets on the concentration of surfactants and show the different behaviors of microjets in the presence of anionic, cationic, and neutral surfactants. These findings have important implications on the motion of self-propelled microjet engines.