A. Dahlgren

Antiferroelectric liquid crystals with 45° tilt - a new class of promising electro-optic materials

Abstract Antiferroelectric liquid crystals with a tilt angle of 45 degrees have very interesting optical properties, which seem to have been overlooked so far - perhaps because such materials have hardly been available. We have prepared a four-component mixture of partially fluorinated compounds with a SmCa* phase in the interval between 27.4°C and 121.6°C, in which the tilt angle θ saturates at 45 degrees for T≤80°C, and we investigate the optical properties, theoretically and experimentally. One of the surprising features of 45 degree materials is that they permit a remarkably high contrast by virtue of an excellent dark-state, in spite of the fact that AFLC materials are notoriously difficult to align. This is because a 45° AFLC turns out to be (negatively) uniaxial instead of biaxial. We describe these properties and propose a number of potentially interesting new applications, including a polarizer-free display mode and a three-level “phase-only” modulator.

Parameter characteristics of a ferroelectric liquid crystal with polarization sign reversal

Abstract The compound shows the unusual behaviour of sign reversal in the spontaneous polarization P versus temperature. This was first reported by Goodby, Chin, Geary and Patel (1). We have now a fairly complete set of data concerning polarization, tilt angle, optical response time, helical pitch and dielectric constant. These parameters are discussed, in particular concerning their temperature behaviour, in order to elucidate the mechanism behind the polarization reversal and its physical significance.

Synthesis and Electro-Optical Properties of Some Ferroelectric Liquid Crystals Derived from Lactic Acid

Abstract We have synthesized two series of liquid crystals, viz. 4′-(ω-(2-ethoxy) propoxy)alkoxyphenyl 4-alkoxybenzoate, 2, (abbreviated Cm-Cn-OEt*) and 4′-(ω-(2-chloro)propoxy)alkoxyphenyl 4-alkoxybenzoate, 3, (abbreviated Cm-Cn-Cl*). Compounds belonging to the latter mainly exhibit smectic A and B phases while the former show enantiotropic smectic C* at or near room temperature as well as A and smectic phases of higher order. The magnitude of the spontaneous polarization is moderate (–4 nC/cm2). There is no alteration in sign for the spontaneous polarization and for the helical pitch as function of the n value. The Cm-C3-OEt* and Cm-C5-OEt* compounds are exhibiting unusually long helical periodicity for a pure compound (30–50 μm). Compounds of series 2 also show a close relationship between spontaneous polarization and tilt angle giving a practically temperature independent ratio P/θ, making the definition of a material constant Po = P/θ meaningful.

Optic, electrooptic and dielectric properties of novel antiferroelectric liquid crystal compounds

Abstract The optic, electrooptic and dielectric spectroscopy characterisation of novel four-ring thiophene-based chiral esters comprising suitably 5, 5′-disubstituted 2, 2′-bithiophene (antiferro- electrics) is reported. The two compounds exhibit interesting hysterises in their phase sequences, and we show that even whole phases (e.g. their relatively wide ferri-phases) may be suppressed by the surface interactions in thin cells.

Pitch measurements on chiral smectic liquid crystals in the C*, Ca* and Cγ* phases

Abstract The pitch and handedness of the helix have been measured in three substances possessing the helical C*, Cy* and Ca* phases. A comparison between measurements on free-standing films and conventional samples between glass plates is made, showing a smearing-out influence from the glass surfaces in the second case. Hence the freestanding film gives a closer approximation to the intrinsic bulk property.

Identification of the liquid crystal phases of some chiral Schiff bases

The mesophases of eleven chiral Schiff bases are identified by miscibility examinations, using the contact method. Some of these compounds exhibit medium pitch (2-3 μm) chiral smectic C mesophases ...

Electroclinic Light Switch

A light switch based on the electroclinic effect in the chiral orthogonal smectic phases (A * , B * and E * ), aligned in a bookshelf geometry, is described. The switch consists of a linear polarizer, a double electroclinic cell and a λ/4 optical plate. The switch can be used as an optical element for performing logic operations based on different polarization states of the light. Corresponding to zero electric field and to opposite sign of the applied electric field the light after passage of the switch, can be in one of three different polarization states