Reversible Chemotaxis of Janus Emulsion Droplets

Organisms move in response to chemical stimulation as chemotaxis, recognizing environmental changes and transducing that information into directed motion. Emulating nature, many reported motile soft colloids utilize chemical stimuli to interact with their environment, including liquid which move using their fluid interface to generate Marangoni flows by physical or chemical stimulation. Current reports which utilize Marangoni-flow directed motion have been limited to a single programmable interface, yielding uncontrolled or unidirectional motion. We present a system where chemotactic speed and direction are reversible and responsive to the environment, using dynamically reconfigurable biphasic droplets whose shape is also responsive to the environment. A bi-phasic droplet in a binary surfactant mixture moves dependent on the magnitude of gradients and the droplet morphology, mutually determined by interfacial tension balance and competition. For droplets with two exposed interfaces to the environment, each interface is programmable to a separate gradient acting on the droplet, where droplet behavior is dependent on both the magnitude of the external gradients and the surface area that gradient acts upon. The reconfigurable nature of the presented system enables interactive and adaptive behaviors in response to a changing local environment. With this internal degree of freedom and response to the environment, we present theoretical and experimental insight into the generation of multi-responsive adaptive soft-matter. Utilizing droplet interactions with the environment in kind, the behavior of the droplets can be utilized to understand novel gradients. Soft-matter with internal feedback mechanisms are adaptive agents in response to bio(chemical) stimulation, such as the decision to move toward or away from a stimuli.