High-frequency acoustic domains in liquid crystals

A mechanism for the formation of one-and two-dimensional domains in planar nematic and cholesteric liquid crystal samples in an ultrasonic field is discussed. A new approach to the analysis of this phenomenon based on the concepts of nonequilibrium hydrodynamics and taking into account the relaxation properties of the mesophase is experimentally substantiated.     

Schlieren textures in smectic liquid crystals

The details of well developed schlieren textures have been observed at smectic C and B modifications. In these textures whole numbered point singularities occur and inversion walls with strong similarities to nematic schlieren textures. It is shown that the occurrence of smectic schlieren textures is due to suppositions derived theoretically by Nehring and Saupe. These suppositions are: tilted structure and plane layers with the layers parallel to the supporting glass slides. In smectic B inversion walls occur which allow to conclude on variable tilt angles of the structure.     

Liquid crystals: applications and industry

Liquid crystals (LCs) are mesogenic phases of matter which combine liquid fluidity with crystalline solid properties. Precise knowledge of the molecular orientations – close to the boundaries and within the material bulk – is necessary for understanding their flow behaviour, especially in microfluidic settings. While the boundary conditions are set, passively, by surface-induced molecular orientations, the bulk orientation in flow is determined, actively, by the anisotropic coupling between the flow and the molecular orientation. Together, the surface and the bulk orientations offer a range of topological constraints within microfluidic channels, which affect the evolution and sustenance of flow-induced phenomena in LC-based systems. The concept of topological microfluidics can be extended to different classes of anisotropic fluids, allowing us to explore and to employ such fluids as complex functional materials for microfluidics, thereby significantly broadening the reach of conventional microfluidics.     

Colloidal structures in confined nematic liquid crystals

Colloidal structures in confined nematics offer novel routes for designing complex optical materials with micrometre and submicrometre functionality. In this paper, we review some of our recently assembled colloidal structures that form in confined nematic cells. We present effective elastic binding via nematic distortion as a mechanism for the assembly of two-dimensional colloidal crystals of elastic dipoles and elastic quadrupoles. We introduce entangled colloids as novel types of structures, where particles are topologically bound by delocalised defect loops, producing robust and possibly chiral structures. The concept of hierarchical assembly is demonstrated in colloids with particles of various scales. In cholesteric blue phases, the assembly of three-dimensional colloidal crystals is shown based on naturally occurring three-dimensional arrays of trapping sites produced by blue phases.     

Chiral resolution in bent-core nematic liquid crystals

This paper presents the currently available experimental evidence for the occurrence of chiral resolution in bent-core nematic liquid crystals. The observation of chiral domains in these systems is discussed in context with other indications for the unique character of the nematic phase in bent-core materials, which challenge our understanding of nematic phase behaviour. Two possible mechanisms for the emergence of macroscopically chiral domains are exposed; the spontaneous resolution of chiral bent-core conformers and the occurrence of helical twist bend deformations due to a unique propensity for spontaneous bending of the nematic director in bent-core materials. The latter proposition is put into context with the recently developed cluster model, as overall it appears more appropriate to consider bent-core nematic systems as self-assembling-self-organising fluids with a hierarchical domain structure.     

On orientational fluctuations in nematic liquid crystals

The factors determining the spectral density of intrinsic optical noise of a nematic liquid crystal (NLC), caused by fluctuations of director orientation in a frequency range of 0.01–1 Hz, have been experimentally established for the first time for (10–100)-μm layers, characterized by rigid anchoring at the boundaries and a quasi-homeotropic macrostructure. A model developed for estimating the spectral density of this noise for an NLC layer with a previously deformed macrostructure and finite molecular anchoring energy has been approved.