Catalytic nanomotors

Abstract

Autonomous catalytic nanomotors with nanometer-to-micrometer dimensions convert chemical energy into mechanical energy via a catalyzed chemical reaction. They represent an emerging nanotechnology field and promise important technological advances in drug delivery, disease treatment, transport, assembly, and other applications at the nano-scale. This dissertation focuses upon the fabrication of catalytic nanomotors using dynamic shadowing growth, motion characterization, motion engineering, and understanding the propulsion mechanism. Unique nanomotor structures were fabricated using dynamic shadowing growth, and novel swimming behaviors are presented and analyzed. Two different major propulsion mechanisms are responsible for catalytic nanomotor movement: bubble propulsion and self-electrophoresis. For catalyst-coated insulator backbone nanomotors, a bubble propulsion model is proposed. The driving force depends upon the fluid surface tension and the concentration of H2O2, and the model predictions are supported by the data. A torsion balance directly measures the driving force. The force is per nanomotor and has a linear H2O2 concentration dependence with a slope of N per percentage of H2O2. Asymmetric Pt/Au catalytic micromotors were fabricated also, and the exposed Au surface area A is changed systematically to alter the speed given by . Swimming behaviors are altered by designing various geometrical shapes; dynamic shadowing growth allows for a wide range of shapes and sizes. Various swimming behaviors are exhibited by altering the geometry, and/or changing the location of the Pt catalyst. Multi-component rotational nanomotors consisting of Pt coated TiO2 nanoarms grown upon ~ 2.01 μm diameter silica microbeads are fabricated. The structures rotate at a rate of 0.15 Hz per % H2O2 concentration. Tadpole-shaped nanomotors with Pt coated on the microbeads swim in circular trajectories. The swimming trajectories are fine-tuned by altering the arm length, and simulations based on the method of regularized Stokeslets, provided by the University of Illinois Urbana-Champaign, correctly capture the experimental trends. The formation of nanomotor systems by the self-assembly of two or three nanomotors together is presented. These systems are more complex than previously studied ones, and we show examples of 2-nanomotor spinning clusters, helicopter nanomotors with multiple parts, and V-shaped spinning nanomotors that are assembled using ferromagnetic materials to couple the spinners to microbeads.