During the process of microbubble shrinking, the gradual adsorption of amphiphilic molecules and decrease of bubble area would lead to the interfacial enrichment of amphiphiles, for both insoluble or soluble surfactants. For soluble surfactants the enrichment may be because the typical time of surfactant desorption is larger than that for bubble shrinking. The increasing areal density of surfactant at the interface would lead to a decrease in surface tension until a certain value areal density is reached (see Figure ). Typically, the areal density corresponds to an extremely low (close to 0) surface tension, at which a compressed amphiphile monolayer is formed.