Catalytic Self-Phoretic Active Colloids

Active Janus colloids are nano to micron sized colloids, capable of propelling themselves through fluidic environments. Localised, asymmetric catalytic reactions on the colloidal bodies are used to decompose a dissolved ‘fuel’ to produce motion. Active Janus colloids have been proposed for applications in microfluidic transport. Currently active Janus colloids are restricted in their practical applications due to the randomised nature of their trajectories over time and their low yielding production methods. This thesis is focused on active Janus colloids prepared by physical vapour deposition, which utilise hemispherically coated platinum as a catalyst to decompose aqueous hydrogen peroxide. Many theories and mathematical models have been reported and are discussed in this thesis as to the precise nature of the mechanism of motion. To contribute to this discussion, active colloids were prepared with different surface functionalities on the non-catalytic section of the Janus colloids. The results indicated that the hydrophobicity of the non-catalytic face influenced the propulsive velocity of the active colloid which informs on the relationship between the fluid and the phoretic body. In an effort to produce active colloids with non-random, prescribed trajectories, the symmetry of the catalytically active layer was incrementally broken and found to introduce an additional angular velocity. The magnitude of angular velocity was controllable through production parameters. An alternative, more scalable fabrication method was developed during the course of this work. A solution based fabrication method was found to successfully produce active colloids in high concentrations which were phoretically analogous to those previously fabricated. Finally, an investigation into the effect of the active cap shape and surface coverage was conducted. Significantly, this study found that symmetrically active colloids displayed propulsive behaviour. The suggestion that asymmetry is not required for producing enhanced motion can be used to inform and simplify future fabrication methods