Light-induced 2D micro-swimmers at the nematic-isotropic interface of a thermotropic liquid crystal

Much of the inspiration in developing synthetic active materials comes from biological systems, such as bacteria species that move in water in the presence of light. It would be interesting to study the motile behavior of these micro-structures within structured liquids as thermotropic liquid crystals (LC). Therefore, we designed a novel LC-compatible system inspired by the structure of Paramecia.

Our system consists of quasi-2D micron-sized platelets that are formed after drying droplets of a water-soluble dye on a glass surface. The platelets are then immersed in 5CB. Since the local temperature of the medium is tunable while shining light on a dyed platelet, it locally induces the nematic-isotropic (NI) phase transition of the LC, as the absorbed energy is released as heat. The platelet then self-propels after harnessing the energy from the surroundings and transforming it to generate mechanical impulses. The irregular morphology of the platelet maximizes the area of light absorption and contributes to the local symmetry-breaking in the system. As a result, a net force is induced on the platelet, and hence the platelet moves. An introduction to molecular dynamics and continuum simulations is also given to figure out the local physical phenomena occurring in the system.