Topological defects in nematic liquid crystals of active colloidal rods

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Active liquid crystals are out-of-equilibrium systems that display intriguing dynamic phenomena, arising from the interplay between topological defects and collective motion. Here, we propose to experimentally study for the first time (i) the dynamics of topological defects in the active colloidal nematic phase and (ii) the interplay between these topological defects and collective dynamics, in three dimensions, at the single particle level, and with full control over the defects. To reach these objectives, we first use a combination of advanced colloidal synthesis and surface modification techniques in order to develop a model system of active colloidal rods of controlled size, aspect ratio and surface properties. We then confine this newly developed model system in microfluidic channels, where the colloidal rods form a nematic liquid crystal. Topological defects will be induced in the nematic phase using specific geometric constraints, which can be varied to control the locations and strengths of the defects, or by optical trapping techniques. Finally, we use state-of-the-art confocal microscopy and sophisticated image analysis techniques to follow, in real time and 3D real space, both the individual particle motion and the collective dynamics in the system. Our work will thus provide experimental verification of the intriguing link between topological defects and collective dynamics in active liquid crystals and inspire novel theories and simulation codes capable of capturing the intrinsic complexity of coupling structure, orientation and activity.