Domain walls in vertically vibrated monolayers of cylinders confined in annuli

Abstract

Liquid-crystalline ordering in vertically vibrated granular monolayers of metallic rods confined in annuli of different sizes is examined. The annuli consist of circular cavities with a central circular obstruction. In the absence of the central obstruction, rods of low aspect ratio exhibit global tetratic order, except for the existence of four small defected regions which restore the tetratic symmetry broken by the circular confinement. However, very different configurations are observed in the annuli, with a complex structure consisting of alternating layered regions separated by tetratic domain walls. We use concepts of equilibrium elastic theory for liquid crystals and topology along with arguments based on dissipation mechanisms to qualitatively explain this behavior. The results show that selective confinement of vertically vibrated monolayers of rods could be used as a tool to study the creation and dynamics of various types of defects in ordered systems.

Particle-resolved topological defects of smectic colloidal liquid crystals in extreme confinement

“…7 b), resulting in a larger relative λ 0 / p , has the opposite effect. Extending our state diagram towards shorter rods at a fixed density, we further anticipate the emergence of stable tetratic structures 41 , since smectic order is generally destabilized 47 .…”

“…Here we approach the defect structure of smectic liquid crystals from the most fundamental particle-resolved scale and quantify both their positional and orientational disorder simultaneously in theory and experiment. In doing so we study two-dimensional smectics composed of lyotropic colloidal rods whose size enables a direct observation [37][38][39] , while they have the advantage over granulates 40,41 that they are fully thermally equilibrated. The colloidal samples are exposed to extreme confinements possessing an annular shape and dimensions of a few particle lengths.…”

Particle-resolved topological defects of smectic colloidal liquid crystals in extreme confinement

“…Here we approach the defect structure of smectic liquid crystals from the most fundamental particle-resolved scale and quantify both their positional and orientational disorder simultaneously in theory and experimnent. In doing so we study two-dimensional smectics composed of lyotropic colloidal rods whose size enables a direct observation [37][38][39] , while they have the advantage over granulates 40,41 that they are fully thermally equilibrated. The colloidal samples are exposed to extreme confinements possessing an annular shape and dimensions of a few particle lengths.…”

Topology of orientational defects in confined smectic liquid crystals

“…In this Letter, we demonstrate that extremely confined smectic systems can be effectively described in terms of topological defects in the tetratic order due to the strong preference of smectic layers to tilt at a grain boundary by approximately 90 • . The tetratic topology is thus not only important in systems with tetratic bulk symmetry [79][80][81][82] but also a vital ingredient to a comprehensive picture of frustrated smectics. In detail, we identify quarterinteger tetratic disclinations, which materialize in pairs at the extremities of grain boundaries, as the elementary topological unit of smectic liquid crystals.…”

“…Beyond the chosen methodology, our topological toolbox can be readily employed to illustrate the coexisting nematic and tetratic orientational order of frustrated smectics in free-energy based theoretical studies [15,78,[89][90][91], granular experiments [80][81][82] or molecular systems [92][93][94]. Regarding nonconvex confinements [78] or two-dimensional manifolds [65,95], our set of building blocks can be supplemented by a line connecting two negative tetratic charges.…”