Stephen Kitson

Controllable alignment of nematic liquid crystals around microscopic posts: Stabilization of multiple states

Nematic liquid crystal materials are rod-like molecules that align in a locally common direction called the director. This gives rise to anisotropic properties that are used in electro-optical devices such as displays, which usually consist of a sandwich of material between two substrates. The behavior of the director at the substrate surfaces is a critical design consideration, and a wide variety of surface treatments has been reported. Most are dominated by molecular interactions, e.g., high surface energy materials that give homogeneous alignment (the director parallel to substrate). The elastic properties of nematics can also be used to influence alignment by shaping the surface on the micron scale. The potential that this offers to engineer device properties is relatively unexplored; to date, the majority of results reported concentrate on essentially two-dimensional effects. Here we show that the three-dimensional configuration of nematics around microscopic posts results in multiple stable director orientations, and can be used in particular to implement bistable displays with a broad range of control over the optical and switching properties.

Biomimetic Reflectors Fabricated Using Self-Organising, Self-Aligning Liquid Crystal Polymers

The photograph shows a polymer reflector that mimics the colour and underlying molecular structure of a golden beetle. It is formed from self-organizing layers of photopolymerised liquid crystal. These require an aligning layer, but we show that a layer of the material can be used as to self-align subsequent coatings, enabling the construction of complex structures by sequential coating of engineered materials.

Bright color reflective displays with interlayer reflectors

A good solution to the reflective display of color has been a major challenge for the display industry, with very limited color gamuts demonstrated to date. Conventional side-by-side red, green and blue color filters waste two-thirds of incident light. The alternative of stacking cyan, magenta and yellow layers is also challenging--a 10% loss per layer compounds to nearly 50% overall. Here we demonstrate an architecture that interleaves absorbing-to-clear shutters with matched wavelength selective reflectors. This increases color gamut by reducing losses and more cleanly separating the color channels, and gives much wider choice of electro-optic colorants.

43.2: Colour Plastic Bistable Nematic Display Fabricated by Imprint and Inkjet Technology

Plastic displays require new manufacturing processes and techniques to achieve acceptable cost and performance. We present a novel additive, low temperature, atmospheric pressure, self-aligned means of fabricating a plastic, bistable, full colour LC display. By using imprinting rather than photolithographic patterning, a scalable, low cost manufacturing route is possible.

Designing liquid crystal alignment surfaces

We have previously shown that tilted micron-scale posts can be used to generate uniform liquid crystal alignment. By considering the geometry and symmetry of individual surface features in more detail, we have been able to demonstrate finer control of alignment, eliminate the need for tilted structures, and show multidomain alignment.

Computing with liquid crystal fingers: models of geometric and logical computation.

When a voltage is applied across a thin layer of cholesteric liquid crystal, fingers of cholesteric alignment can form and propagate in the layer. In computer simulation, based on experimental laboratory results, we demonstrate that these cholesteric fingers can solve selected problems of computational geometry, logic, and arithmetics. We show that branching fingers approximate a planar Voronoi diagram, and nonbranching fingers produce a convex subdivision of concave polygons. We also provide a detailed blueprint and simulation of a one-bit half-adder functioning on the principles of collision-based computing, where the implementation is via collision of liquid crystal fingers with obstacles and other fingers.

Electrowetting pixels with improved transmittance using dye doped liquid crystals

Electrowetting display pixels have been created using a dye doped liquid crystal as the dielectric liquid in a simple electrowetting architecture. In addition to electrowetting, the dye doped liquid crystal reorients, giving two mechanisms to modulate the light. We show that realignment of the liquid crystal, due to the electric field, occurs both before and during electrowetting. The transmission of the pixel has been compared to the transmission of a pixel containing an isotropic liquid, using a simple mathematical model, and we show that electrical realignment of the LC improves the transmission of the pixel. We show a 6.8% gain in the transmission during electrowetting, and before electrowetting occurs.

Color plastic bistable nematic display fabricated by imprint and ink-jet technology

— Plastic displays require new manufacturing processes and techniques to achieve acceptable cost and performance. A novel additive, low-temperature atmospheric-pressure self-aligned means of fabricating integrated plastic substrates for full-color LCDs and a bistable LC mode based on microstructure alignment are presented. By using imprinting rather than photolithographic patterning, a scalable, low-cost manufacturing route is possible. A 2-in.-diagonal 128 × 128-pixel display was made to demonstrate the principles involved, which has retained an image for in excess of 2 years.

High throughput technique for characterizing liquid crystal alignment in complex geometries

We present a high throughput technique for characterizing liquid crystal electro-optic devices. We show that the optical transmission as a function of incident light polarization for an untwisted nematic device doped with dichroic dye can be simulated as a birefringent slab with uniform tilt and azimuthal alignment angles. Although the actual liquid crystal alignment may be more complex, these slab angles provide the basis of a rapid assessment technique. Implementation of the experiment using machine vision allows many measurements to be made in parallel and so very high throughput characterization of devices is possible.