In this work, we present the synthesis and characterization of a new series of wholly-aromatic copolyesters derived from the condensation of various weight fractions of 4,4'-(o- phenylenedioxy)dibenzoic acid (OPDB) and substituted terephthalic acid (BTA) with 2-phenylhydroquinone (PHQ). The Higashi method, involving tosyl chloride and pyridine as solvent, was employed to yield polymer with significant molecular weight. These polymers are intended to enable accessible clearing transition and to control the balance of stiffness and toughness in melt-spun fibers systematically. We report the synthetic details along with characterization of quiescent phase behavior and morphology.

The rigid chain microstructure of thermotropic liquid crystal polymers (TLCPs) permits an ordered morphology to form consequently giving these materials exceptionally high strength. X-ray and neutron scattering techniques effectively determine the semi-crystalline structure of TLCP but lack the spatial resolution needed to detect morphological changes occurring on sub-micron length scales. This research develops an electron optical technique to resolve the local orientation of LCP fibers at resolutions on the order of 100-300 nm. This paper outlines the essential elements of this technique and presents preliminary results showing systematic morphological changes of LCP fiber as a function of position across the fiber diameter.

Addition of an ABA triblock copolymer to a midblock-selective solvent can, depending on copolymer/blend composition and the magnitude of block-block and block-solvent interactions, result in the formation of a physical network that is stabilized by aggregates of the incompatible A-block. In this work, an ABA copolymer with a nematic side-chain liquid crystal midblock is added to a low-molar-mass nematic liquid crystal (LC) in an effort to produce a comparable copolymer network and bind the LC matrix. This nanostructured system, designated a physically crosslinked liquid crystal (PCLC), may not suffer as much from the constraint-induced LC anchoring problems associated with conventional polymer-dispersed liquid crystals (PDLCs). Results presented here demonstrate that hierarchical phase behavior must be carefully considered in the design of PCLCs.

We have investigated the effect of various processing variables on the magnetic field orientation of a liquid crystalline epoxy. By using a modified fractional factorial design, we created an empirical model which can be used to predict the degree of orientation as a function of these variables. The model predicts the correct qualitative trends, namely that orientation increases with increasing magnetic field strength, increases with increasing time in the field, and decreases with increasing B-staging. The model also reveals some surprising effects of B-staging on the degree of orientation.

Electron microscopy methods have been used to investigate the structure and morphology of a hexagonal columnar mesophase, formed by novel amphiphilic and dendrimeric liquid crystals. Alignment of the columns is examined by a surface condition that is suitable for the molecular architecture. For all the materials investigated, columns aligned perpendicular to an evaporated carbon surface. In the case of asymmetric amphiphilic compounds, planar alignment of asymmetric compounds was induced by a water surface. However, planar alignment on water was not possible for a symmetric dendrimer. Based on analysis of electron diffraction and images, the dimension and the stiffness of columnar assemblies is found to depend on molecular architecture.

In this report, we describe the fabrication and photo-induced alignment of ultrathin films of small molecular azobenzene dyes and polyelectrolytes using the alternate polyelectrolyte deposition (APD) technique. The molecular self-assembly process were investigated by QCM, ellipsometry, UV-vis spectroscopy, X-ray reflectometry, and other surface sensitive spectroscopic and microscopic methods to correlate with film formation parameters. The importance of layer ordering and dye aggregation phenomena is emphasized. We then utilized polarized UV-light to induce photo-alignment of these ultrathin films and observed high anisotropies dependent on the dye, layer preparation and thickness. Fabrication of hybrid LC cells using a nematic LC reveal that in-plane homogeneous alignment is influenced by the anisotropy of the dye aggregates.

Thermotropic liquid-crystalline behavior of various complex salts, which are structurally simple amphiphiles without rigid cores, was evaluated by differential scanning calorimetry, polarizing optical microscopy, and X-ray diffractometry. The phosphonium salts, consisting of positive phosphorus and negative chloride ions, were found to show a smectic A phase in which a homeotropic structure was formed spontaneously. It is significant that the phosphonium salts possess an advantageous feature as thermotropic liquid crystals and show a stable liquid-crystalline phase and a simple phase transition behavior in comparison with commonly available ammonium analogs. Furthermore, the introduction of divalent metal ions into the amphiphiles was revealed to result in enhancement of the thermal properties. Although the ammonium chlorides as parent compounds showed no liquid-crystalline phase (or indistinct transition behavior), the ammonium complexes possessing tetrachlorometalate ions exhibited clearly the smectic A phase in the expanded temperature range. Additionally, through the evaluation of dipolar alignment in the solid-state phosphonium assembly by second harmonic generation, it was assumed that the self-assembly can be regarded as layered polar thin films produced by two-dimensional ionic layers with an overall permanent electric polarization.

Photoconductivity of a mesogenic tetraphenylporphyrin (TPP) is shown in relation to the mesomorphic phase transition behavior. The TPP mesogen shows two types of mesophases having smectic-like order (lamellar mesophases : DL and DLC phases named in this work) and the photocurrent changes stepwise at the phase transitions with non-Arrhenius dependence whilst the darkcurrent tends to be Arrhenius. The hole mobility was measured for the random domain cell and was found to be faster than 10−4 cm2v−1sec−1 in the mesophases. The cell used for the photocurrent measurements was a sandwich-type one using two ITO glass slides as electrtodes and show rectification behavior for the crystal and the low-temperature mesophase (DLC) in contrast to non-rectification of photocurrent in the high-temperature mesophase (DL). These properties of charge carrier migration as an electronic process are profoundly related to molecular order as well as molecular motions in mesophase.

Nematic liquid crystal filled with Aerosil particles, a prospective composite material for optoelectronic application, has been investigated by static light scattering and Photon Correlation Spectroscopy (PCS). The Aerosil particles in filled nematic liquid crystals (FN) form a network structure with LC domains about 2500 Å in size with a random distribution of the director orientation of each domain.

We found that the properties of 5CB are considerably affected by the network. The N-I phase transition in filled 5CB was found to be smeared out and depressed. PCS experiments show that two new relaxation processes appear in filled 5CB in addition to the director fluctuation process in bulk. The slow relaxation process, with a broad spectrum of relaxation times, is somewhat similar to the slow decay, which is observed in confined nematic liquid crystal.

The middle frequency process was assigned to the director fluctuations in the surface layer formed at the particle-LC interface. The decay function describing this relaxation process is a stretched exponential (β ≍ 0.7). The temperature dependence of the relaxation times of the middle frequency obeys the Vogel-Rilcher law. Such a temperature dependence, accompanied by a broad spectrum of relaxation times suggests that the dynamics of the director fluctuations near the Aerosil particle-LC interface is glass-like.

Nematic liquid crystals filled with Aerosil particles are new heterogeneous materials important for different optoelectronic applications. These materials are suspensions of small silica particles, about 10-17 nm in diameter, dispersed in nematic liquid crystals. The particles are known to form a network structure dividing liquid crystal into domains with linear size approximately 250 nm. We used both hydrophilic and hydrophobic particles, filling them with the nematic liquid crystal-5CB.

Broad band dielectric spectroscopy (1 mHz - 1.5 GHz) was applied for the investigation of these materials. Two bulk-like modes due to the rotation of molecules around the short axis and the tumbling motion were observed in filled 5CB. Additionally, a low frequency relaxation process and the dispersion of dielectric permittivity due to conductivity were also observed. The modification of the surface of the particles has stronger influence on the slow process and is less important for the molecular modes. The contribution of the slow process for the hydrophilic sample to the total polarization is greater than for the hydrophobic sample. In addition, the corresponding characteristic frequencies are lower for the case of hydrophilic samples. These facts suggest that the low frequency relaxation is an Aerosil particle-liquid crystal interface related phenomena and the origin of this process maybe explained on the basis of surface induced polarization.

Several colorless compounds with dielectric anisotropy in the 10-50 range were studied. The absorption spectra, phase transition temperature, birefringence, dielectric anisotropy and visco-elastic coefficient of these compounds were measured.

The templated syntheses of our zeolite-type frameworks of metal halides frequently result in the formation of glassy phases or viscous liquids that might be described as ambient temperature molten salts. Having discovered that certain of these materials exhibit remarkable birefringence, we have investigated the structure of both the glass and liquid forms of alkylammonium templated zinc chloride materials by neutron and X-ray diffraction, as well as DSC and polarizing microscopy techniques. Further template control using alkylammonium surfactants as directors has yielded an entire family of liquid crystalline materials with up to 90% inorganic content. The compositional dependence of the structure of these liquid crystalline phases suggests that these materials are best described as “solvent-free” lyotropic liquid crystals.

The light absorption properties of anthraquinone dye in different hosts are compared in order to demonstrate the influence of the dye-liquid crystal interactions on dye order parameter. Surprisingly, the anthraquinone dye have a higher order parameter in liquid crystalline mixtures of positive dielectric anisotropy as well as in a liquid crystalline mixture of negative dielectric anisotropy (S = 0.71-0.82). We studied the Heilmeier displays use homogeneous alignment. The display is operated at the reverse mode, transparent at zero field. The switching voltage between the bright and dark states for these displays is 2-4 volts, depending on host liquid crystal and cell configuration.

While many liquid crystal studies have focused on static structural and electronic properties, dynamic factors such as molecular anisotropy, partial ordering and structural fluctuations have hindered descriptions linking liquid crystalline properties at the molecular level with the macroscopic level properties (as measured experimentally). In this paper, we examine the transition from molecular to bulk properties for the nematogen 5-alkyl-cyanobiphenyl (5CB), using both molecular dynamics and quantum mechanical calculations. We perform molecular dynamics simulations on a collection of molecules in the nematic phase, sample the trajectory to create a representative collection of structures, and perform electronic structure calculations on the sampled structures.

Both dielectric permittivity and AC conductivity are important properties of LC materials for use in displays. By taking typical LC substances as examples, quantitative data are presented on these properties. From microscopic point of view, permanent dipole of LC molecules and ions contained in LC materials play important roles in these electric properties. Quantitative discussions are also presented on these microscopic characteristics. Theoretical understandings of these properties are reviewed, providing good explanations of the relation between these microscopic and macroscopic properties.

We have recently proposed the ridge and fringe-field multi-domain homeotropic (RFF-MH) mode for improving viewing angles of thin-film-transistor driven liquid crystal display (TFT-LCD) panels (4). We also demonstrated that the RFF-MH structures are suitable for high resolution desk top TFT-LCD panels (5). In this paper we demonstrated that the RFF-MH method is also suitable for the high-end large-area notebook application since it provides wide viewing angles with a high optical transmission. The ridge structure is constructed on top of the indium tin oxide (ITO) layer of the color filter (CF) substrate, and can be fabricated during the color filter process. The cell process of the RFF-MH panel is compatible to the conventional TFT-LCD cell fabrication process. It requires one extra photolithographic step; however no rubbing treatment is required.