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Presently, nematic polymer dispersed liquid crystals (PDLCs) that are used in switchable glazing technology require constant power to operate and, moreover, exhibit unwanted haze at wide viewing angles. In this paper, a novel switchable glazing technology, based around a bistable electro-optic effect in the Smectic A liquid crystal phase, is described which does not require constant power to operate or exhibit haze. The application of a low-frequency (100 Hz) voltage induces an optically opaque state due to the motion of ionic material whereas the application of a higher frequency AC (1 kHz) voltage induces a haze-free clear state. Multistable (greyscale) operation is possible through the application of intermediate frequencies or voltages; the threshold voltages of the effect were found to range from 36 to 66 V rms. Any voltage-induced state is preserved indefinitely after removal of the voltage leading to low power consumption.

Lasers were invented some 40 years ago and are now used in a plethora of applications. Stable liquid crystals were discovered at about the same time, and are now the basis of a large display industry. Both technologies involve photonics, the former in the creation and use of light and the latter in the control and manipulation of light. However, it is only recently that these two mature technologies have been combined to form liquid-crystal lasers, heralding a new era for these photonic materials and the potential for novel applications. We summarize the characteristics of liquid crystals that lead to laser devices, the wide diversity of possible laser systems, and the properties of the light produced.

A newly synthesized low molar mass liquid crystal having a flexible mesogenic group attached to methylene siloxane exhibiting smectic A phase has been used as a host for 2% (wt./wt.) dichroic dyes. The electro-optic properties of these guest–host mixtures have been studied as a function of temperature, frequency and the applied voltage. At low frequency (≲1 Hz), turbulent scattering texture was induced influenced by conduction mechanism. This texture was transformed to a clear homeotropic state due to dielectric reorientation of the smectic molecules at high frequency (>2 kHz). These materials have shown storage effects similar to monomeric and polymer smectogens. The effects of dichroic dyes on the electro-optic performances have been discussed. These systems are expected to prove functional materials for electronic displays.

On the basis of DSC calorimetry and thermo-optic (TOA) measurements the mesomorphic properties of the strongly polar Schiff bases family, 4-chlorobenzylidene-4′-alkylanilines (CBnA), are presented. Two kinds of mesophases were found: smectic A and smectic B. For the first time detailed calorimetric properties of the investigated family are presented and discussed. Very narrow smectic A phase for the nonyl, decyl, undecyl and dodecyl derivatives was detected. Smectic mesophases in butyl, pentyl and dodecyl derivatives are monotropic. These results are compared with our earlier results [1].

Optical and electro-optical properties of side chain liquid crystalline polymers are described. The polymers studied were homopolysiloxanes with mesogenic side groups separated from the polymer backbone by flexible polymethylene spacers of varying length. The effect of the flexible spacer on the phase properties and electric field effects will be discussed. Low frequency a.c. fields induced a turbulent scattering texture, whilst at higher frequencies (> 1 kHz) a homeotropic alignment was obtained. The latter effect leads to high contrast displays which are durably stored at temperatures well above the glass transition. Various parameters affecting the response of the polymers to applied fields will also be discussed. These include temperature, frequency and magnitude of the electric field, film thickness and the length of the flexible spacer.

Several well defined average values of the rotatory diffusion constant D of a polydisperse system can be obtained using the initial slope of the free decay of different electro-optical phenomena and different degrees of orientation. The type of average depends also on the orientation mechanism. The type of average and its relation to the corresponding moments of the size distribution, which have been previously misused, are derived for rod-like and disc-like particles, different mechanisms of orientation, and two types of electro-optical effect: birefringence (or dichroism) and light scattering in an electric field. Re-examination of the agreement claimed by previous authors between averages of D measured by this technique and calculated from a distribution of size derived from electron micrographs illustrate the difficulties of the measurements at saturation of orientation, and the role of an exact knowledge of the orientation mechanism. Possible experiments are discussed. Two parameters analytical distribution functions, well suited for the expression of the differen moments appearing in the theory, are indicated.

The static and dynamic properties of solutions of a side chain polysiloxane liquid crystal polymer have been studied in a cyanobiphenyl nematic host as a function of concentration and temperature. Refractive index measurements were carried out on aligned samples and the data used to determine the macroscopic order parameter, S, using Haller's method. Photon correlation spectroscopy has been used to measure ( k 22 γ 1 ) for the pure nematic solvent and the solutions. From these measurements it appears that the static properties vary slowly and linearly with increasing polymer concentration whilst the dynamic or viscoelastic properties change markedly. This change has been attributed to γ1, the twist viscosity, and the results have been discussed in terms of the function of the siloxane polymer backbone.

Smectic side chain polysiloxane polymer liquid crystals have been used to demonstrate high-resolution laser writing on thin (∼20 μm) polymer films. Depending on the pulse energies (typically

Magnetic and electric fields have been used to determine the splay ( k 11 ) and bend ( k 33 ) elastic constants in a series of polymer/monomer liquid crystal solutions using the well known Freedericksz transition technique. Measurements have been carried out as a function of concentration and temperature. The polymer used was a smectogenic polysiloxane side chain liquid crystal with both cyanobiphenyl and benzoate ester side groups. The monomeric solvent was the nematogen 4-n-pentyl-4′-cyanobiphenyl. All of the solutions studied were nematogenic up to a concentration of 40% w/w. It has been shown that k 11 , k 33 and k 33 k 11 all decrease with increasing polymer concentration and that at high enough concentrations k 33 k 11 tends to become independent of temperature. The implications of these results are discussed in terms of the performance of the most common liquid crystal display, i.e. the twisted nematic device.

The optical and de Kerr effects have been measured for the nematogen octyl-cyanobiphenyl (8 CB) as a function of temperature in the isotropic phase. By using pulse methods dynamic properties have been determined and the pretransitional behaviour examined in terms of the Landau-de Gennes model. The constants a , v , T * and ( T c – T * ) of this formalism have been given.

A simple inexpensive electric field birefringence cell is described. This cell has a low strain birefringence, low cell volume and is particularly suited to studies on macromolecular solutions and pure liquids. The correct functioning of the cell is illustrated by measurements on poly(ρ-benzyl-L-glutamate) solutions. Further improvements are suggested.