EXPERIMENTS AND MODELING OF MOTILITY AND CHEMOTAXIS OF PSEUDOMONAS AERUGINOSA

Ph.DPH.D. IN MECHANOBIOLOGY (FOS

Liquid Crystal Microdroplets from Complex Binary Liquid Mixtures

Liquid crystals and binary fluid mixtures are fields of soft matter, which individually offer unique properties for applications in displays, drug delivery, sensors and optoelectronics. They are both responsive to external stimuli and may take part in self-assembly processes. When a liquid crystal becomes a component of a binary fluid mixture, one can envisage that the complex interplay presents interesting phenomena. In this work, the thermotropic liquid crystal, 4-cyano-4’-pentylbiphenyl (5CB) was combined with methanol (MeOH) to form a partially miscible liquid mixture with an upper critical solution temperature (UCST). The research presented herein is in four parts. First, the formation of liquid crystal-rich droplets by temperature-induced phase separation was investigated. The tuning of early-stage isotropic and nematic liquid crystal-rich droplet size and number through manipulation of nucleation and growth conditions was studied by exposure to simple temperature protocols in the range of 35 C to -5 C. Second, the dynamics of late-stage phase separation was investigated. This isotropic liquid-liquid crystal binary system presented a unique advantage, wherein the interactions of a binary liquid reaching equilibrium could be visualised through the optical properties of the liquid crystal,enabling a comparative study of bulk and microscale phase separation. Thirdly, the effect of surfactants and particles on this binary liquid system was investigated. Block co-polymers were found to increase nucleation points, and silica nanoparticles were found to lead to porous structures. Finally, the reversibility of the binary system was exploited for the production of microparticles. Reactive mesogens were incorporated into the liquid crystal 5CB, and photopolymerisation was employed to create temperature-responsive porous microparticles, which could be tuned in its size and ability to shrink and swell. Furthermore, the binary liquid could be separated from the microparticle by heating. The results achieved through this work offer a potential for the development of finely tuned liquid crystal droplets and microparticle production by simple temperature control, and offer novel insights into liquid-liquid phase separation, and the optical manipulation of liquid crystals