Rotation of topological defects by trapped micro-rods in the nematic phase of a liquid crystal

The dynamics of rod-shaped micro-particles, trapped within a topological defect, was investigated. It is demonstrated that there is an attractive interaction force between particle and defect, which is of the order of F ≈ 30 pN, pulling the free micro-rod into the defect core, directing it along the direction of escape. Application of an electric field can induce motion of the trapped rod along the macroscopic path of a circular trajectory, which results in a circular drag motion of the defect's director field. The direction of circular motion can be clockwise or counter-clockwise with equal probability, independent of the sign of the defect. The electric field dependence of trajectory diameter and angular velocity are investigated, and it is found that these lead to a velocity, which is largely independent of electric field and particle-defect rotation direction.