Controlled Motion of Polymeric Microparticles at Interfaces and in Solution

The research scope of this thesis is the study and the characterisation of the motion of polymeric non-propulsive and propulsive microparticles on the surface and in the bulk. Characterising the motion of these particles as well as investigating different methods to control their motion and to perform useful tasks (e.g. in vivo drug delivery, cargo transport in microfluidic systems and device assembly) has provoked great interest among scientists in recent years. Since the introduction of catalytic nanorods and colloidal nanoswimmers, many attempts have been made to transform the random motion of these particles (due to Brownian phenomena) into a controlled motion, towards a desired location. The work described here is divided into three main categories: Regulating the speed and direction of the particles by modifying the substrate they move upon, steering the particles to a target using gradients of fields such as magnetic, electric, concentration, etc. and controlling the inherent propulsion direction of the particles by fabricating swimmers that are capable of producing a range of trajectories from rotation to linear translation. These methods involve controlling the speed of rolling particles by altering their affinity to the substrate, exploiting the trajectories of pH-responsive particles to produce statistical accumulation within a gradient, directing propulsive magnetic particles via an external uniform magnetic field, utilising the motion of spiralling swimmers to achieve mixing at the microscale and adjusting the area-to-volume ratio of catalytic swimmers to optimise their propulsion speed which is a function of reaction rate on their surface. In addition, the characteristics of these techniques such as their reproducibility, accuracy, autonomy and complexity are also discussed.