Cyclic Siloxanes, bearing mesogenic groups, connected with the backbone via aliphatic spacers exhibit phases analogue to the classic calamitics. Bearing two different mesogenic groups, these materials can be considered as cooligomers, whose degree of polymerization is given by the H-siloxanes used. These cooligomers consist of a mixture of molecules with substitution patterns determined by the statistics of the addition reaction of the mesogenic groups to the H-siloxane. Two types of materials are available, crosslinkable and non crosslinkable. As most important applications may be mentioned: Cholesteric reflectors and filters, storage materials for optical informations, retardation plates and pigments for iridescent or polarizing coatings.

An overview is presented for a generic approach to low molar mass liquid crystalline materials capable of vitrification into morphologically stable, optically anisotropic thin films. Potential applications as polarization control devices, optical notch filters, and luminescent elements will be explored. Preliminary data for defect formation and annihilation will also be presented to illustrate an advantage of low molar mass materials over polymer analogs.

Based on the extensive database collected for model glass-forming liquid crystals with various mesogenic groups attached to benzene, cubane, cis- and trans-cyclohexane, and all-exobicyclo[ 2.2.2]oct-7-ene, it was found that the glass-forming ability and morphological stability are determined by a delicate structural balance between the volume-excluding core and the pendant group, and the stereochemical features of the hybrid system.

Based on a series of model nematic and chiral-nematic compounds as well as a polymer analog, it was found that the annihilation of defects in a VLC system occurs at a much faster rate than its polymer analog. In chiral-nematic blends, the degree of structural similarity between the nematic host and the chiral dopant plays an important role; a wider biphasic region contributes to a slower annihilation process.

Effects of molecular structures on the phase transition temperatures, dielectric anisotropy, elastic constant, and refractive indices of diphenyl-diacetylene liquid crystals are analyzed.

Physical properties of mono-, di- and tri- fluorobenzenc derivatives with different core structures consisting of 3-ring system were measured. By introduction of fluorine atoms, phase change telnperaturcs decreased, nematic temperature range narrowed, optical anisotropy and elastic constant decreased, and dielectric anisotropy increased. From a calculation with MOPAC ver. 6.0, it is clear that elastic constants depend upon shapes of molecules under a restricted condition.

By blending the investigated compounds as main components, different nematic mixtures, having low threshold voltage low viscosity, large optical anisotropy or wide nematic range, which are suitable for specific applications for AM-LCD, were obtained

A number of new chiral binaphthol (BN) derivatives with different substituents in the 6,6'-positions in open and bridged forms have been synthesized. Their possible liquid crystalline properties and their helical twisting power (B) of three different nematic liquid crystals (LCs) were investigated. Derivatives with spatially extended substituents in the 6,6'-positions (e.g. styryl or vinil) show unusual high helical twisting power (up to 120 μm–1). A direct correlation between the magnitude of β and the length of the substituents was found.

From the different temperature dependence of β of the open and bridged BNs, a molecular model was developed relating the molecular conformation and twisting power

Mesomorphic properties and temperature dependence of the hydrogen bonding between urethane bonds (H-bonding) for side chain type liquid crystalline polyurethane(SLCPU)s were studied by thermally controlled FT-IR spectroscopy. A remarkable change in the strength of H-bonding for SLCPUs with a flexible chain in the polymer backbone(flexible SLCPUs) was displayed near the phase transition temperatures, while small changes in the strength of H-bonding for SLCPUs with a rigid moiety in the polymer backbone(rigid SLCPUs) was influenced by a mesogenic group in the side chain and the flexible chain length in the polymer backbone. Furthermore, in order to study the influence of H-bonding in rigid SLCPUs, polyurethane derivatives with methyl group were synthesized replacing hydrogen in urethane bonds. No mesomorphic properties for polyurethane derivatives obtained were exhibited. It was concluded that H-bonding played an important role to exhibit mesomorphic properties of rigid SLCPUs.

A new series of side chain liquid crystalline-amorphous diblock copolymers has been successfully synthesized using chiral mesogens. Anionic polymerization techniques have been used to make these monodisperse diblock materials. Preliminary studies suggest that these microphase segregated diblock copolymers exhibit a smectic C* phase. This mesophase exists between and above the glass transition temperatures of the two polymer blocks. Synthesis and characterization of these novel materials are discussed.

Mixtures of mono- and diacrylates showing a nematic phase were polymerized in an electric field. The orientation of chromophores in the thin films depended on the direction of dipole moment as well as the polymerization conversion of the liquid crystalline monomers.

Novel side chain type liquid crystalline polymers, polythiophene and poly(aryleneethynylene) [PAE], containing a mesogenic group in the side chain were synthesized. Polythiophene derivatives were obtained by dehalogenative polycondensation with zero-valence nickel complex under mild condition. PAE type polymers were obtained by coupling dihalo aromatic compound with diethynyl aromatic compound. Their thermal properties were examined by differential scanning calorimetry, optical microscopy and X-ray diffractometry. All polymers exhibited a smectic or nematic mesophase depending upon the polymer backbone and pendant mesogenic group. Polythiophene derivatives exhibited electrochemical activity. Annealing polythiophene derivatives led to a lower oxidation potential and a higher conductivity. The degree of the orientation of the polymer backbone was supported by polarized UV-vis measurement. An effective conjugated length became longer by introducing thiophene rings into the polymer backbone. A high quantum yield of fluorescence was observed for PAE type polymers.

Eight new 4'-acyl-4-biphenylol esters 5a∼h were synthesized and their mesomorphic properties were tested by PM and DSC. These compounds have wider mesomorphic transition temperature ranges and higher clearing points. The compound 5g in which there is no chiral carbon exhibits a stripped focal conic texture in its Sc mesophase. The effect of the molecular structure on the liquid crystal properties was discussed.

Ten new chiral liquid crystalline compounds I1–10 of 4′ -acyl-4-biphenylol (S) -4- (2-methyl-l-butoxy) benzoates were synthesized and their mesomorphic properties were tested. They are all smectic liquid crystals with wide temperature ranges and except for compounds I1, all exhibit a Sc*phase. The influence of molecular structure on phase behavior is discussed.

The synthesis of two series of side-chain liquid crystalline polyoxetanes and polyoxiranes containing 4-alkanyloxybiphenyl-4′ -yl (2S,3S)-2-chloro-3-methylvalerate side groups is presented. Differential scanning calorimetry, polarizing optical microscopy, and X-ray diffractometry reveal smectic mesomorphism for all obtained polymers. Most of the prepared polyoxetanes present smectic A and chiral smectic C phases. The polyoxetane containing tweleve methylene units in the spacer is the only one showing two enantiotropic smectic A and B phases. All of the obtained polyoxiranes display two enantiotropic smectic A and B phases. Although the polyoxetane and polyoxirane backbones are more flexible than the polymethacrylate backbone, side-chain crystallization do not occur in any of the synthesized polymers.

Based on common molecular model, polymer liquid crystals of hard-rod and flexible main-chain are studied statistical mechanically. The hard-core repulsion and also the attractive potentials are assumed between molecules. The nematic-isotropic phase transitions, and molecular orientations at interfaces in polymers and polymer-liquid crystal composite systems are discussed.

Molecular dynamics simulations have been used to characterize the development and longevity of associations between cholesterol and biphenyl mesogens when attached to linear siloxane oligomers by flexible spacer groups. Single substituents, alternating substituents, and diblock and triblock arrangements of the substituents were considered. The backbone and spacer groups allow sufficient flexibility that long-lived associations between cholesterol mesogens form quite rapidly, as do more fluid associations between biphenyl and cholesterol mesogens. The study of the individual mesogen interactions and how these lead to larger scale aligned structures has provided insight into the nature of the liquid crystalline state in these materials.

We have developed a numerical technique to investigate the effect of different Frank elastic constants on the microstructure of liquid crystalline materials. In particular the technique is applied to predict microstructure in polymeric materials where the splay elastic constant is high and the twist elastic constant is low. It is found that such a combination of elastic constants leads naturally to the twist escaped features seen experimentally.

We have recently begun investigating the rheological behavior of blends containing thermotropic liquid crystalline polymers (LCPs) and isotropic polymers. To aid us in our studies, we have designed a unique instrument for simultaneous visualization of morphology evolution and rheological measurements. Rectilinear shear is used, with a top glass bar being translated relative to a fixed bottom glass bar. The sample is heated by conduction from mica heaters embedded in the substrate materials supporting the bounding glass bars. Shear forces are obtained by measuring the (small) deflection of the bottom glass bar and heating assembly which is designed to be slightly compliant in the flow direction while rigid in direction normal to the sample.

Cross-sectional observations of the molecular orientation in typical display modes are demonstrated. ECB (Electrically Controlled Birefringence), Bend and TN (Twisted Nematic) cells are fabricated using a UV curable liquid crystal material. LC cells are photo-polymerized with applying appropriate AC voltages and cut into slices to obtain the cross-sectional images. As a result, frozen molecular orientation states in a cross section of the LC cell are successfully visualized clearly using a polarizing microscope.

Liquid crystals may possess macroscopically aligned structural, electrical and optical properties when oriented in external fields which leads to a wide range of applications including optical filters, displays, and data storage devices. Combining the properties of thermosets [1, 2] with the properties of liquid crystals (LC) is a logical step towards creating new materials. The development of liquid crystalline thermosets (LCT) has been motivated by their potential use in structural applications and the need for more adaptable polymeric materials with tunable strength and stiffness as well as tailored mechanical anisotropy. It is known that mechanical properties of conventional thermosets are determined by many factors including curing agent, filler, degree of cure, crosslink density, glass transition temperature, and accelerator. In LCT's all of these factors will ultimately be controlled by the both the molecular organization and orientation of the LC phase.