Difference in the interaction of nano-diameter rod and tubular particles with a disclination line in a nematic liquid crystal*

Defects created by the nematic liquid crystal (LC) due to the presence of particles, spherical as well as rod-shaped, generate strong forces, inducing also particle trapping into a defect line. However, even in presence of particles such as carbon nanotubes (CNTs), not expected to create defects, even if in elongated bundles, we observe trapping into a 1/2 LC defect line but with differences in the dynamics compared to aggregates of rod-shaped Mo₆S₂I₈ nanowires. The reason is attributed to the topological difference of the particle shapes. Even if both types have cylindrical shape, the hollow nature of CNTs make them not homotopically equivalent to the Mo₆S₂I₈ nanowires and this inequivalence holds also for the LC around them. The nanowires induce defects in the LC close-by their surfaces. In contrast, multi-wall CNTs, being hollow, do not form defects even close to their ends. However, structural tube bending, as observed in the used multi-wall CNTs, presumably due to the ultrasound dispertion treatment, together with the strong planar anchoring of LC at their bare surfacs, induces deformations in the LC, enabling attraction forces with the defect line.