Light-activated micro-swimmers in a thermotropic liquid crystal

Over the last decade, studies of artificial micro-swimmers have significantly mimicked the dynamics of those in nature. However, most research has been focused on isotropic liquids hosts, with fewer studies dedicated to structured media. In this work, we designed two self-propelled systems at different length scales in a nematic fluid. The first one consists of solid platelets with sizes of hundreds of microns, formed after drying droplets of a light-absorbing dye. The second one comprehends Janus silica particles half-coated with titanium. Both systems are immersed in a thermotropic liquid crystal (LC), and their mobility is triggered by light. The light-absorbing materials are heated, consequently inducing a localized LC nematic-isotropic (NI) phase transition. The inhomogeneous distribution of light-absorbing spots contributes to the unevenly formed NI interface. As a result, the platelets and Janus particles move. We show the differences between both systems’ dynamics and optical responses. A discussion of the characteristics that induce mobility in each case is also presented. This research helps to unveil the micro-swimmers’ dynamics at different length scales and different geometry, immersed in a highly structured media.