Abstract

Research in the microfluidic sector has seen serious growth since the 1980s and much progress has been made towards the realisation of true lab on a chip (LOC) devices. However, despite the amount of work put into the design and applications of these chips, there has been a noticeable lack of innovation into the control of flow inside these microfluidic platforms. Conventionally flow is controlled via external pumps and solenoid valves which hinder the scalability of the system. Stimuli-controlled manipulation of discrete micro-sized “vehicles” offers a novel method for controlling flow inside fluidic platforms, while also offering many unique advantages. These include external manipulation of individual or multiple droplets simultaneously while also opening the possibility of using these droplets as micro-vessels for chemical reactions, cargo transport to desired destinations, dynamic sensing, leak detection and drug delivery. Two novel methods for stimuli-controlled movement of micro-sized droplets are presented in the following chapters of this thesis that include chemotaxis and electrotaxis. These single component droplets are self-propelling and are guided to specific destinations through chemically generated Cl- gradients. The droplets consist solely of the ionic liquid (IL) Trihexyl(tetradecyl)phosphonium chloride ([P6,6,6,14][Cl]). The movement of the droplets is controlled by the triggered release of the [P6,6,6,14]+, a very efficient cationic surfactant, which is a constituent of the IL droplet. Several applications are explored for these droplets. Additionally, polymeric hydrogel walkers containing photochromic spiropyran molecules are studied for their ability to achieve photo-controlled movement at the liquid-solid interface.