(31c) Engineering of Self-Propelling Particles That Move in Programmed Trajectories and Haul Cargo

The fabrication of complex self-motile particles is an emerging topic of fascinating potential, yet few principles of particle propulsion have been studied and few concrete applications exist to date. We will report the progress in addressing the challenges of designing physical mechanisms of moving such particles, and identifying areas of their practical use. First we will discuss how external uniform AC electrical fields can be used as means of providing energy, propelling and controlling the motion of Janus metallo-dielectric spheres and miniature semiconductor diodes. The asymmetry of these particles makes them move by particle-localized AC and DC electrohydrodynamic propulsion. We will demonstrate how the diode particles can be steered by controlling the symmetry of the AC field and will hypothesize how an additional level of complexity can be engineered to turn them into prototypes of self-propelling microdevices. In the second part of the talk we will present a new class of gel-based self-propelling particles moving by Marangoni effect in a programmed oscillatory mode. These gel boats floating on the water surface are driven by a hydrogel reservoir releasing an ethanol flux that is periodically disrupted by the bulk flows around the particles. The pulse interval and the distance propelled in a pulse by these gel floaters were interpreted based on the rate of ethanol mass-transfer. The model allowed us to design particles that perform “dances” of repeatable periodic sequences of forward/backward, or rotary steps, and travel in complex pre-programmed trajectories on the liquid surface. We will also present new types of functionalized self-propelling floaters driven by surfactant release that can find applications as mixers and cargo microcarriers, and may serve as a new platform for environmental remediation.