Interest in the synthesis of optically active smectic liquid crystals has increased considerably since the advent of a fast switching, bistable, electrooptic device configuration based on their ferroelectric properties. A number of structurally separate ferroelectric liquid crystal phases have been defined which possess differing properties. These types of phase can be utilized in different forms of application. The structures of the various ferroelectric smectic phases and the types of material which exhibit these modifications are discussed in detail. The design and engineering of materials to suit certain device criteria is related to the properties of the smectic ferroelectric phases. A relationship between the absolute spacial configuration of the optically active materials which exhibit ferroelectric smectic phases, the twist direction of the phase and the direction of the spontaneous polarization is developed.

A Commentary on the paper ”Liquid‐crystalline behaviour in the n‐alkyl gluconamides and other related carbohydrates„, by B. Pfannemuller, W. Welte, E. Chin and J.W. Goodby. First published in Liquid Crystals, 1, 357‐370 (1986).

the pressure-temperature phase diagram of 4-(2′ methylbutyl)phenyl 4′-n-nonyloxybiphenyl-4-carboxylate (9OSI) has been determined by optical microscopy and found to be extremely linear. This compound exhibits smectics A,C.I,G' and H' phases. X-ray measurements on polycrystalline samples are also discussed.

Using x-ray and optical methods we have probed the structural organization of an antiferroelectric twist grain boundary phase (TGBC(a)) lying between the regular antiferroelectric smectic-C (SmCa*) and the smectic-Q (SmQ) or isotropic phase. We find that the twist axis is everywhere perpendicular to the local smectic layer normal and that the helical superstructure is incommensurate with the smectic layer structure. The twist grain boundaries consist of a periodic lattice of alternating +1/2 and -1/2 dispirations, i.e., unit screw dislocations in combination with half unit disclinations. The molecular tilt plane is alternatingly parallel and perpendicular to the twist axis. We find that the optically measured tilt angle in the SmCa* phase is smaller than that measured by x rays, which is the opposite to what is found in the SmC* phase. This means that the core part tilts less than the end chains in the SmCa* phase, while it tilts more in the SmC* phase. On entering the TGB phase a clear decrease is measured in the tilt angle. This is explained by the elastic influence from the disclinations, which appear in this phase.

Physical theories concerning the structures and properties of chiral smectic liquid crystals abound, however, very few are of practical use in the design and subsequent synthesis of materials. The development of macroscopic theories, although very useful in the explanation of physical phenomena, are not readily transferable to the microscopic state. Thus, the design of materials depends more on a qualitative approach supported by property-structure correlations than it does on quantitative deliberation However, viewing the formation and stabilisation of mesophase structures from the microscopic molecular aspect can lead to some very interesting perspectives. In this article, crude or gross molecular shapes are used to investigate local packing arrangements of chiral molecules in layered mesophases. The formation of helical macrostructures is readily described using this form of modelling, and in turn the formation of antiferroelectric and twist grain boundary phases can be rationalised in terms of property-structure correlations.

Novel chiral two ring compounds possessing phenylethenoate moieties were synthesized and their liquid crystalline properties determined. Some of these compounds were found to exhibit SmC*γ, AF and SmC*A phases, whereas in other compounds only SmA* and SmC* phases appear. The influence of the molecular structure on the appearance of SmC*γ, AF and SmC*A phases is discussed. The basic electro-optical properties of the homologous series of (S)-(E)4-(1-methylheptyloxycarbonyl)phenyl 4-alkoxycinnamates, in which SmC*, SmC*γ, AF and SmC* A phases appear, were also investigated. High values of spontaneous polarization, low threshold voltages and fast switching times at room temperature were observed.

By studying the optical textures and the field-induced effects of the recently discovered TGBCAphase we have developed a qualitative model of the microscopic organization of the phase. Inside the smectic blocks, the molecular tilt plane of the local anticlinic structure is perpendicular to the helix of the TGBC A phase. The grain boundaries consist of a regular lattice of +1/2 and -1/2 dispirations; i.e. unit screw dislocations combined with half unit disclinations. Whereas all screw dislocations have the same sign, the sign of the half unit disclinations alternates in adjacent dispirations. Hence, in the grain boundaries the molecular tilt plane between adjacent dispirations is alternately parallel and perpendicular to the TGB helix.

In order to utilize the developed and readily available TFT techniques for surface-stabilized ferroelectric displays the development of formulations with significantly lower birefringence than commonly used today is necessary. The compounds presented here as basis for achiral hosts have structures which are based on difluoroterphenyls except that they have alicyclic ring systems attached to the aromatic core in place of one of the phenyl rings. Mixtures based on these compounds have been prepared and assessed in terms of their transition temperatures and birefringence with reference to the parent terphenyls.

We report ellipsometric measurements on freely suspended films of chiral liquid-crystal compounds near their smectic-A - smectic-C transition. The temperature difference between the surface and the bulk transition is found to vary considerably within a homologous series. In two compounds possessing a fluorinated alkyl chain an unexpected sign inversion of the spontaneous polarization in the ferroelectric smectic-C phase is observed which occurs only in thin but not in thick films.

This paper reports on the dielectric and electro optical studies of two ferroelectric liquid crystals having TGBA phases. Complex dielectric permittivities have been measured in planar aligned cells in the frequency range of 10 Hz to 10 MHz. Bias dependent measurement were performed in the S-C+ and in the TGBA phase. In the S-C* phase three different collective relaxation processes, the Goldstone mode, the Domain mode and the Soft mode were detected for both the substances. In the TGBA phase Soft mode has been observed in one of the compounds without bias field whereas the Soft mode in the other compound was observed only after the application of a bias field. The dielectric results shows that bias induced alignment once achieved does not change even after switching off the bias voltage. It has been observed that the dielectric characteristics of TGBA phases can be similar to that of normal smectic A*; or cholesteric phases, depending upon the temperature interval of the TGBA-phase. The results have been discussed.

We describe several important aspects of surface smectic ordering prior to the onset of bulk ordering in chiral smectic materials. Above a direct isotropic - smectic A (I-A) and nematic - smectic A (N-A) transition in the bulk, there exists an in-plane molecular tilt that is linearly proportional to an applied electric field. While for the I-A transition, this molecular tilt is relatively confined within the surface smectic layer, for the N-A transition, it can elastically propagate into the bulk nematic phase. For the former case, the temperature dependence of this in-plane molecular tilt is much stronger than that for the latter. Our results suggest that the phase sequence, the range of the smectic A phase, and the magnitude of molecular chirality play a significant role in the nature of the surface smectic A ordering.

Detailed heat-capacity measurements have been carried out on free-standing liquid-crystal films of n-heptyl-4'-n-pentyloxybisphenyl-4-carboxylate to investigate the nature of transitions related to surface crystal-E order. Distinct thermal hystereses are observed. Upon heating from the temperature range exhibiting surface crystal-E order and interior hexatic order, anomalous effects on the interior hexatic-B--smectic-A transition, which strongly depend on the film thickness, are evident.

Information on molecular interactions that give rise to the stabilization of various ferroelectric, liquid-crystalline mesophases is important to the realization of their potential utility in a wide variety of optical devices. Understanding the roles that optical activity and optical purity play in the formation and properties of the various smectic phases is therefore of particular interest. In order to study this relationship three new liquid-crystalline materials were prepared, one as a racemic mixture, the other two as the optically active analogues. The optically active isomers appear to exhibit a different mesophase morphology from the racemate. The chiral compounds apparently possess two extra ferroelectric mesophases in comparison to the racemic mixture. The transitions to and from these phases have extremely small enthalpies. An attempt is made to explain the results for the chiral compounds in terms of differing dipolar couplings in the chiral ferroelectric phases. In the racemic mixture these interactions are compromised or scrambled by a loss of asymmetry thus destabilizing these extra phases.

A wide variety of liquid-crystalline derivatives of S-β-citronellol (S-3,7-dimethyloct-6-ene-1-ol) were prepared and found to exhibit ferroelectric smectic phases. The S-β-citronellol was initially hydrogenated to produce S-3,7-dimethyloctan-1-ol (3M7M8OH). This in turn was either brominated, oxidized, or used in an unchanged form to synthesize a range of materials, many of which exhibited smectic C* phases. The magnitude of the spontaneous polarization for a number of these derivatives was measured. Generally, the materials reported were found to have values for their spontaneous polarizations in the range of 5 to 15 nCcm−2. Many of the materials were also found to have short helical pitches in their C* phases, making them useful as unwinding agents in ferroelectric mixtures.

The results of a study of the dielectric response of the liquid crystal BOH8-MPOOBC in the frequency range 5 Hz to 13 MHz, in the vicinity of the phase transition to the ferroelectric phase, in an aligned cell of 2.7 \ensuremath{\mu}m thickness, are presented. At small ac probe fields, critical-like behavior is observed in the dielectric permittivity and the characteristic relaxation time of molecules in the bulk of the sample. At high ac probe fields, a second relaxation appears due to the reorientation of molecules at the cell surfaces. The dielectric strength of the bulk relaxation grows linearly with the spontaneous polarization. The viscosities of the surface and bulk processes, as determined from measured characteristic times and spontaneous polarization, increase in a thermally activated manner for temperatures within the ferroelectric phase. Comparison of frequency-dependent optical response and dielectric response measurements at small applied fields shows that both are due to the same bulk molecular reorientation process.

Common syntheses of phenyl benzoyloxybenzoates generally produce products in low yields. A variety of synthetic pathways were employed in an attempt to increase the overall yield of the final product. It was found that catalytic agents such as boron trifluoride-etherate (BF3 Et2O), 1,3-dicyclohexylcarbodiimide (DCC), and 4-N, N-di-methylaminopyridine (DMAP) were relatively ineffective in these processes. However. protection of the hydroxy moiety of an appropriately substituted benzoic acid with methyl chloroformate, followed by esterification under normal conditions, and deprotection with ammonia in ethanol produces the hydroxy-benzoyloxybenzoate intermediate. This material can be used in further esterifications to produce phenyl benzoyloxybenzoate compounds in good yield. Materials such as the triply reentrant compound 4-n-nonyloxyphenyl 4-nitrobenzoyloxybenzoate (DB9ONO2) can be prepared by this method.

Recently some mono-alkylated derivatives of β-D-glucopyranoside and thio-α-D-mannopyranoside were shown to exhibit liquid crystal properties. The structure of the phase produced by these materials was described as being of a layered smectic type. However, a full classification of the phase was not given. The present investigation defines the phase as smectic A with a bilayer structuring. The lamellar spacings previously found for the phase agree with calculated values for a bilayer ordering in which the carbohydrate moieties overlap to produce an extensively hydrogen bonded structure. The phase was found to be immiscible with the A phases of conventional smectogens because the hydrogen bonding necessary for phase formation is disrupted in binary mixtures.