Topological defect-propelled swimming of nematic colloids

Dynamics of far-from-equilibrium topological defects in nematic liquid crystals (NLCs) can be used as a fundamental propulsion mechanism in microscopic active matter. Here, we demonstrate swimming of topological defect-propelled disk colloids with hybrid anchoring in (passive) nematic fluids through experiments and numerical simulations. Upon rotation of the disk colloids by an external magnetic field, the defects periodically elongate along the disk’s edges and sweep along the disk’s face. This dynamic swim stroke generates stresses with broken symmetries that propel the colloid. Defects elongate significantly adjacent to the disk at higher rotation rates, altering swimming direction. In this regime, the swimming speed and direction are determined by the colloid’s angular velocity, sense of rotation and defect polarity; these effects allow trajectory planning. We study the effective pair interactions of two defect-propelled swimmers, which are highly anisotropic and depend on the microscopic structure of the defect stroke, including the local defect topology and polarity. More generally, this work aims to develop biomimetic active matter based on the underlying relevance of topology.