Abstract
Topological defects in liquid crystals not only affect the optical and rheological properties of the host, but can also act as scaffolds in which to trap nano or micro-sized colloidal objects. The creation of complex defect shapes, however, often involves confining the liquid crystals in curved geometries or adds complex-shaped colloidal objects, which are unsuitable for device applications. Using topologically patterned substrates, here we demonstrate the controlled generation of three-dimensional defect lines with non-trivial shapes and even chirality, in a flat slab of nematic liquid crystal. By using the defect lines as templates and the electric response of the liquid crystals, colloidal superstructures are constructed, which can be reversibly reconfigured at a voltage as low as 1.3 V. Three-dimensional engineering of the defect shapes in liquid crystals is potentially useful in the fabrication of self-healing composites and in stabilizing artificial frustrated phases.
Highlights
Topological defects in liquid crystals affect the optical and rheological properties of the host, but can act as scaffolds in which to trap nano or micro-sized colloidal objects
In a nematic liquid crystal, rodlike molecules are packed such that they have no positional order but have orientational order with the long axes of the molecules pointing along the ‘director’, defined by a unit vector, n, with head–tail symmetry
Optical vortices, which are light beams carrying a topological charge, are generated via light–matter interactions in a liquid crystal slab with topological defects[12,13]; colloidal particles doped in liquid crystals generate a network of disclinations that confer the composite the properties of a self-healing gel[14,15]; and disclinations have been used as scaffolds in which to trap conductive or plasmonic particles to potentially realize three-dimensional micro-wires or tunable metamaterials[16,17,18,19,20]
Summary
Topological defects in liquid crystals affect the optical and rheological properties of the host, but can act as scaffolds in which to trap nano or micro-sized colloidal objects. Here we demonstrate the controlled generation of three-dimensional defect lines with non-trivial shapes and even chirality, in a flat slab of nematic liquid crystal. Liquid crystals find applications in diverse scientific disciplines, ranging from optics, electronics, mechanics, biology and cosmology[1,2,3,4,5] Their usefulness derives from their broken rotational symmetry, which gives rise to spontaneous alignment that can be controlled through boundary conditions at interfaces or by an external field. We demonstrate controlled generation of a threedimensional disclination network by confining a liquid crystal slab between two substrates that possess topological surface anchoring conditions, that is, the substrates contain a singular point or defect around which the orientational easy axis rotates by an integral multiple of p. The concept of defect engineering we propose introduces the possibility of fabricating liquid crystal composites with controlled structures that may be used in a variety of applications
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