Development and Study of Chemopropelled Cargo-Carrying Vehicles in Fluids

Developing droplet systems capable of controlled movement has attracted a lot of attention because of their applications in different areas such as bioassays and high-throughput synthesis. Droplet movement has been achieved utilizing chemical, thermal or optical stimuli, with chemical stimulus (to develop a chemotactic system) and light stimulus (to develop a phototactic system) two of the most common. In such systems, the movement of droplets is based on generating tension gradients at the droplet interface resulting in a Marangoni flow in the direction of the gradient and droplet motion in the opposite direction by conservation of momentum. This dissertation focuses on the development and characterization of new phototactic and chemotactic droplet systems. The phototactic droplet systems are based on light irradiation of a photoactive spiropyran or protonated merocyanine that is within the organic droplet, which moves due to the resulting spiropyran/merocyanine photoisomerization reaction changing the surface tension of the droplet/water interface. The photoactive materials used were either a commercially available nitro-functionalised spiropyran (SP) or the dodecylbenzenesulphonate salt of the protonated merocyanine of SP (MCH+:DBS-). The characterization of the phototactic systems and investigation of the mechanism of droplet motion was explored using UV-visible, fluorescence and resonance Raman spectroscopies, along with the study of the interfacial tension (IFT) change of the droplets.