Design of Reactive Surfactants that Control the Locomotion Mode of Cell-Sized Oil Droplets

Abstract

The self-propelled motion of micrometer-sized oil droplets in nonequilibrium systems has attracted considerable attention as a primitive type of inanimate chemical machinery. We investigated the dynamics of n-heptyloxybenzaldehyde droplets in a cationic reactive surfactant solution with the objective of controlling the movement of self-propelled oil droplets. (1) We designed a novel molecular system that lengthened the locomotion time of oil droplets by using estercontaining cationic surfactants, (2) we evaluated the dynamics of oil droplets in a solution of a gemini cationic surfactant with various alkyl chain lengths in the linker to induce a locomotion mode change of the droplets and induce a conformational change in the flexible linked molecule, and (3) we examined the behavior of oil droplets in a microchannel in a solution containing a gemini cationic surfactant that has a carbonate linkage. These droplets exhibited two motions during the hydrolysis of the carbonate linkage, generating two surfactant species. Keywords: Cationic surfactant, hydrolysis, ion-exchange reaction, nonequilibrium system, oil droplet, self-propelled motion.