'Sweeping rods': the sideways self-propulsion of micro-rods
Self-propulsion is the motion of particles by self-generated forces in a specific direction. Design of artificial self-propelled systems was inspired by living species which use the propulsion for searching for food and escaping from predators. Nowadays these systems are of interest for micro-sized devices like sensors, systems, which transport medicines in human body, and micro-pumps. On these length scales in aqueous solutions viscous force dominates over the inertial forces and the motion proceeds in low Reynolds regime. To be propelled at low Re particles should perform asymmetric motion. One of the approaches is to use field gradients (e.g. arises from catalytic reactions) as a power source. The central goal of the project is to understand the self-propulsion mechanism in order to make micro-motors more efficient. The system of study will consist of bimetallic micro-rod which performs sideways motion, the type of motion which is not yet sufficiently studied. However, the investigation of this geometry is of interest because it provides the increased effective area compared to previously studied models. We will implement a simple and robust method of fabrication of Janus micro-rods by electrospinning of polymeric fibers with subsequent coating of their two sides by sputtered metals (e.g. Pt/Au). The bi-metallic rods will be propelled perpendicular their long axis when placed in reactant solution due to the different catalytic reactions on the opposite sides of the particle. Experimental study of 2D motion in the close proximity of boundaries and 3D motion in density matched solution will be investigated with optical, fluorescence and fast confocal microscopy. We will try to elucidate the exact mechanism of self-propulsion in fluids and model the speed and efficiency of the self-propelled rods. In order to obtain the electrokinetic parameters, hydrogen peroxide reaction on different metals will be studied electrochemically. The model will be validated by experimentally observed data obtained from microscopy.