Reacting dislocations drive chirality and shape transitions in tubular crystals

Natural and synthetic tubular crystals, such as microtubules and single-walled carbon nanotubes, often contain dislocation point-defects. When dislocations move through a tubular crystal, they alter the chirality of the lattice, and they may stabilize deformed tube geometries if the crystal is freestanding. In order to elucidate the complex feedback between topological defects, lattice chirality, and tube geometry, we conduct molecular dynamics simulations of patchy spherical particles assembled into free-standing tubular structures with preexisting defects. We demonstrate that stable patterns of dislocations, which are specific to tubular crystals, significantly deform the macroscopic shape of the crystal. In addition, we find dislocation reaction behaviors unique to tubular crystals, with the reacting defects, located several lattice spacings apart, effectively changing their orientations and thus altering the chirality of the lattice. We show that externally applied torsion can be used to control the dislocation motion and even initiate a sequence of elementary defect reactions, resulting in a target defect pattern. Our findings suggest routes to colloidal crystal assemblies with switchable mechanical and electro-optic behaviors.