Willis H. Smith

Liquid crystal birefringence for millimeter wave radar

Abstract Many liquid crystals are found to have relatively high birefringence (Δn) values in the microwave and millimeter wave regions, as calculated from the phase shift induced by their reorientation by magnetic or electric fields. At 30 GHz, Δn values were obtained in the range of 0.08 to 0.18 for eleven liquid crystal mixtures of various types. The most favourable liquid crystal structures for high millimeter wave birefringence are highly conjugated rod-like molecules containing biphenyl, terphenyl, phenylpyrimidine, biphenylpyrimidine, and tolane groups in nematics of positive dielectric anisotropy (Δe). However, other liquid crystal structures including Schiffs base, azoxybenzene, and aromatic ester groups also have substantial birefringence, including nematics with negative and crossover Δe, as well as cholesteric nematics. The Δn varied only slightly at different frequencies of microwave millimeter wave in the 15–94 GHz range. Studies on magnetic and electrical field liquid crystal orientation in ...

Formulation and Predicted Properties of Nematic Eutectic Mixtures of Esters

Abstract Techniques are described both for formulating new nematic liquid crystal (LC) eutectic mixtures and for calculating several of their predicted properties. Ester LC components from various structure classes are used. Emphasis is placed on obtaining mixtures which have relatively short average molecular length, and which are suitable for dynamic scattering electro-optical applications. Examples are given of binary eutectic mixtures made with LC esters of essentially the same molecular length. Selection rules are described for mixing short length components, both from homologous series and from different classes of esters. Approximate class values of birefringence, dielectric anisotropy, and viscosity are assigned to each type of ester structure, based on experimental results in selected mixtures of short molecular length. Properties of multi-component eutectic mixtures are calculated, and comparisons are shown between the predicted and the observed values of melting point, clearpoint, viscosity, di...

Liquid Crystal Alignment Method for Long Lifetime Tilted-Perpendicular Light Valves

Abstract A new technique for tilted-perpendicular alignment (TPA) of liquid crystals on surfaces greatly improved the photostability of the photoactivated liquid crystal light valves (LCLVs) with negative dielectric anisotropy liquid crystals. The operation of surface-perpendicular aligned LCLVs provided a very dark off-state, high contrast images, and high light throughput efficiency. Alkoxy groups bonded on angle-deposited SiO2 gave controlled TPA, in which the tilt angle of LC on the treated surfaces was primarily dependent on the thickness of the shallow-angle deposited SiO2 layer. We have demonstrated improved photostability to high intensity light exposures using this TPA method in hermetically sealed cells. Projection LCLVs with very high contrast and with greater than 10,000 hours of operational stability at 2000 lumens, were obtained using this new TPA method and more stable liquid crystal mixtures.

Diamagnetic Anisotropy Measurements of Nematic Liquid Crystals

Abstract Electro-optic effect of liquid crystals in the presence of a magnetic field was investigated. Two independent techniques: magnetic field dependent threshold voltage and magnetic field-assisted relaxation time, were used to evaluate the diamagnetic anisotropy for three nematic liquid crystals: BDH-E7, RO-TN-103 and ZLI-1132. Correlation between the diamagnetic anisotropy and the molecular structures was obtained. This information is particularly important for synthesizing liquid crystal components with desired diamagnetic anisotropy.

Guidelines For Selecting Or Synthesizing Nematic Liquid Crystals

Principles for selecting or synthesizing liquid crystal mixtures with desired birefringence are analyzed. Based on these principles a liquid crystal mixture exhibiting large birefringence and low visco-elastic coefficient at room temperature was formulated. Optical and electro-optic properties of this liquid crystal were characterized at elevated temperature. Results are compared with those of some commercially available liquid crystals.