title: Topology and self-assembly of defect-colloidal superstructure in confined chiral nematic liquid crystals.
abstract: We describe formation of defect-colloidal superstructures induced by microspheres with normal surface anchoring dispersed in chiral nematic liquid crystals in confinement-unwound homeotropic cells. Using three-dimensional nonlinear optical imaging of the director field, we demonstrate that some of the induced defects have nonsingular solitonic nature while others are singular point and line topological defects. The common director structures induced by individual microspheres have dipolar symmetry. These topological dipoles are formed by the particle and a hyperbolic point defect (or small disclination loop) of elementary hedgehog charge opposite to that of a sphere with perpendicular boundary conditions, which in cells with thickness over equilibrium cholesteric pitch ratio approaching unity are additionally interspaced by a looped double-twist cylinder of continuous director deformations. The long-range elastic interactions are probed by holographic optical tweezers and videomicroscopy, providing insights to the physical underpinnings behind self-assembled colloidal structures entangled by twisted solitons. Computer-simulated field and defect configurations induced by the colloidal particles and their assemblies, which are obtained by numerically minimizing the Landau-de Gennes free energy, are in agreement with the experimental findings.
authors: Department of Physics, University of Colorado, Boulder, Colorado 80309, USA.
authors: M B
authors: MB
authors: Pandey
authors: Department of Physics, University of Colorado, Boulder, Colorado 80309, USA and Department of Electrical, Computer, and Energy Engineering, University of Colorado, Boulder, Colorado 80309, USA.
authors: P J
authors: PJ
authors: Ackerman
authors: Department of Physics, University of Colorado, Boulder, Colorado 80309, USA.
authors: A
authors: A
authors: Burkart
authors: Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia.
authors: T
authors: T
authors: Porenta
authors: Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia and J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia.
authors: S
authors: S
authors: Žumer
authors: Department of Physics, University of Colorado, Boulder, Colorado 80309, USA and Department of Electrical, Computer, and Energy Engineering, University of Colorado, Boulder, Colorado 80309, USA and Liquid Crystal Materials Research Center and Materials Science and Engineering Program, University of Colorado, Boulder, Colorado 80309, USA and Renewable and Sustainable Energy Institute, National Renewable Energy Laboratory and University of Colorado, Boulder, Colorado 80309, USA.
authors: Ivan I
authors: II
authors: Smalyukh