Improving experimental procedures for assessing electrical properties of advanced liquid crystal materials

Electrical measurements of liquid crystals are a standard part of their material characterisation. Typically, such measurements are carried out using a sandwich-like cell of a single thickness. In this paper, we show that interactions between ions and substrates of a liquid crystal cell result in the dependence of the direct current electrical conductivity of liquid crystal materials on the cell thickness. The obtained experimental results combined with modelling point to the existence of ions of several types and to the competition between ion-releasing and ion-trapping processes in liquid crystal cells. We also propose to use a multi-electrode twin-cell that allows the visualisation of the electric field screening effect in liquid crystals and its mitigation by means of ferroelectric nanoparticles

Electrically tunable birefringence of a polymer composite with long-range orientational ordering of liquid crystals

We report an optical film with electrically tunable birefringence in which the liquid crystals (LCs), mixed with the host polymer, form longrange ordering. The film was prepared through polymerization without phase separation between the LCs and polymers. Driving voltage below 30 V for full switching of birefringence is achieved in a 6 μm-thick film. Electro-optical investigations for the film suggest that the long-range ordering of the LCs mixed in the film caused by polymerization lead to rotations of the LCs as well as optical anisotropy in the film. These films with electrically tunable birefringence could have applications as flexible light modulators and phase retardation films for 2D-3D image switching. © 2014 Optical Society of America.1

Harvesting Single Ferroelectric Domain Stressed Nanoparticles for Optical and Ferroic Applications

We describe techniques to selectively harvest single ferroelectric domain nanoparticles of BaTiO3 as small as 9 nm from a plethora of nanoparticles produced by mechanical grinding. High resolution transmission electron microscopy imaging shows the unidomain atomic structure of the nanoparticles and reveals compressive and tensile surface strains which are attributed to the preservation of ferroelectric behavior in these particles. We demonstrate the positive benefits of using harvested nanoparticles in disparate liquid crystal systems

Drag on particles in a nematic suspension by a moving nematic-isotropic interface

We report the first clear demonstration of drag on colloidal particles by a moving nematic-isotropic interface. The balance of forces explains our observation of periodic, strip-like structures that are produced by the movement of these particles

Ferroelectric Nanoparticles in Liquid Crystals: Recent Progress and Current Challenges

The dispersion of ferroelectric nanomaterials in liquid crystals has recently emerged as a promising way for the design of advanced and tunable electro-optical materials. The goal of this paper is a broad overview of the current technology, basic physical properties, and applications of ferroelectric nanoparticle/liquid crystal colloids. By compiling a great variety of experimental data and discussing it in the framework of existing theoretical models, both scientific and technological challenges of this rapidly developing field of liquid crystal nanoscience are identified. They can be broadly categorized into the following groups: (i) the control of the size, shape, and the ferroelectricity of nanoparticles; (ii) the production of a stable and aggregate-free dispersion of relatively small (~10 nm) ferroelectric nanoparticles in liquid crystals; (iii) the selection of liquid crystal materials the most suitable for the dispersion of nanoparticles; (iv) the choice of appropriate experimental procedures and control measurements to characterize liquid crystals doped with ferroelectric nanoparticles; and (v) the development and/or modification of theoretical and computational models to account for the complexity of the system under study. Possible ways to overcome the identified challenges along with future research directions are also discussed

A practical guide to experimental geometrical optics

A concise, yet deep introduction to experimental, geometrical optics, this book begins with fundamental concepts and then develops the practical skills and research techniques routinely used in modern laboratories. Suitable for students, researchers and optical engineers, this accessible text teaches readers how to build their own optical laboratory and to design and perform optical experiments. It uses a hands-on approach which fills a gap between theory-based textbooks and laboratory manuals, allowing the reader to develop their practical skills in this interdisciplinary field, and also explores the ways in which this knowledge can be applied to the design and production of commercial optical devices. Including supplementary online resources to help readers track and evaluate their experimental results, this text is the ideal companion for anyone with a practical interest in experimental geometrical optics

Fast Birefringent Mode Stressed Liquid Crystal

We report a stressed liquid crystal (SLC) that produce a large shift in phase retardation at submillisecond speeds. The SLC consists of uniformly aligned micro-domains of a liquid crystal dispersed in a polymer structure. Mechanical stress produces uniform alignment, essentially eliminates light scattering, and substantially improves the electro-optic performance. A 22-μm-thick SLC film switches more than 2μm of phase retardation in less than 1ms. The system has a linear voltage response with essentially no hysteresis.</p

Patterned Field Induced Polymer Walls for Smectic a Bistable Flexible Displays

We have obtained a polymer wall-stabilized smectic A liquid crystal to be used for bistable flexible displays. The polymer wall structure optimally connects the two substrates together, thus providing maximum flexibility as compared to the polymer dispersed liquid crystal. Moreover, all the intrinsic bistable properties of the smectic A material are preserved. We analyzed the pixel performance and demonstrated very good electro-optical characteristics, high contrast ratio, and excellent stability of the states. The polymer wall-stabilized smectic A on flexible substrates has high potential to be used as electronic paper.</p