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The grayish–black ternary nitride LixMn2−xN (x≈0.67) was prepared from lithium nitride, manganese powder and nitrogen. The phase adopts an anti-Rutile structural arrangement with lithium and manganese atoms disordered on one site: Space group P42/mnm (No. 136), a=4.68578(9) A, c=2.97762(9) A, Z=2. The electrical resistivity of a sintered pellet (ρ≈8.5·10−3 Ω cm at 250 K) increases slowly as the temperature is decreased (to about 1·10−2 Ω cm at 4 K). Magnetic susceptibility and solid state 6Li-NMR measurements suggest localized magnetic moments on the manganese atoms and probably an antiferromagnetic ordering at about 115 K.

We used simplified Mueller matrix (3×3) method to study the optics of reflective twisted nematic (BTN) displays. We obtained a general analytical solution, which shows how to choose display parameters to achieve high contrast ratio between the two stable states. Our results show that the employment of compensation films provides much more freedom to improve electro-optic properties such as response time, viewing angle dependence and contrast.

We have designed a novel trans-reflective liquid crystal display that utilizes a dielectric mirror and electric controlled birefringence ECB effect of a liquid crystal cell. The visible spectrum is divided into two regions with the transmissive mode operated in short wavelength region and the reflective mode operated in long wavelength region. The display has the advantages: 1 the brightness as a function of applied voltage is the same for both modes, 2 it does not need absorption films such that there is no light loss for the backlight.

We have developed a polymer dispersed cholesteric liquid crystal which exhibits two stable states at zero field: reflecting planar texture and non-reflective focal conic texture. Both states have thresholds under driving voltage pulses. The material can be used to make multiplexed displays on passive matrix. Because the liquid crystal is encapsulated, the dispersion can be coated on plastic substrates to make large size displays. Furthermore, it can be used to make single layer full color displays by using a photo-tuning method.

We analyzed the light emission from a backlight system with a cholesteric broad band polarizer by using Berrman 4×4 method. We found that light intensity in directions with polar angle smaller than 30°o was increased and higher than the back light system with only a linear polarizer. We also designed a light recycling backlight system and calculated the light efficiency.

We have developed two types of polymer stabilized cholesteric dichroic dye displays. In the first type, an anisotropic polymer network perpendicular to the cell surface was formed by photo-polymerization in the homeotropic texture in the presence of an electric field. The polymer network enhanced the hysteresis of the voltage-transmittance curve, and the material can be operated in bistable mode at a bias voltage in the hysteresis loop. In the second type, a random polymer network was formed by photo-polymerization in the isotropic phase at an elevated temperature. The polymer network suppressed the hysteresis, and the material can be operated in gray scale mode. The displays had high on-state transmittance, good contrast ratios, and were suitable for direct view display applications.

We report the first gray scale reflective bistable cholesteric display with dynamic drive. We successfully achieve 8 to 16 levels of gray on a VGA format display at 133 dpi. The image shows good contrast and rich gray depth.

The parameters of the 3-phase dynamic drive scheme depend on the transitions among cholesteric textures, which themselves are strongly temperature dependent. Temperature compensation must be made in order for the drive scheme to work in a wide temperature region. We have developed a compensation method in which the frequency of the driver clock is the only parameter that is required to be adjusted with temperature. Using this simple method, we have achieved consistently high contrast ratio of the display in a wide temperature region.

We have designed drive schemes which can update gradually the content of a bistable reflective cholesteric display. These scheme make use of the “kicking” effect as in addressing STN displays. The cholesteric material is kicked from the planar texture to the focal conic texture step-by-step or vice versa. We have also developed a new cholesteric display cell structure which has a 2 ms homeotropic-planar transition time. Using the new cell structure and the new drive scheme, we have achieved an addressing speed of 0.5 ms/line; the cholesteric display can be operated at a quasi-video rate.

Sorption isotherms and diffusion coefficients of water in a 0.3-mil Kapton polyimide film at 30, 45, and 60°C are reported. The data are well described by the dual mode sorption and transport models at low activities. At high penetrant activities, clustering of water is suggested by a Zimm–Lundberg analysis of the sorption data and the fact that the diffusion coefficient for water decreases with increasing external vapor activity. The effect of temperature on the diffusion coefficients at infinite dilution and the dual mode sorption parameters kD, b, and C are presented and discussed. The magnitude of the activation energy of the diffusion coefficient at infinite dilution, 5.4 kcal/mol, is smaller than the corresponding activation energy in more flexible chain polymers, perhaps suggesting that rather small backbone motions are associated with diffusion of water through the Kapton matrix. The predictions for the isosteric enthalpy of sorption from the dual mode model are presented and compared with the values determined from graphical analysis of the sorption isotherms performed independently without reference to the dual mode sorption model.

We have investigated the rheological properties of the Celanese copolyester with the composition 75 mol% p-hydroxybenzoic acid and 25 mol% 2-hydroxy-6-naphthoic acid (designated as 75HBA/25HNA). Three different samples having inherent viscosities 3.0, 6.0, and 9.2 dL/g were studied. A flow instability is observed at low shear stress which produces an irregularity in the fiber diameter. The surface irregularity becomes less pronounced above a minimum shear stress, indicating that the flow instability originates in the capillary. For these nematic melts, the minimum shear stress marking the onset of more regular flow is found to decrease with increasing temperature and with decreasing inherent viscosity of the copolyester. The die swell ratio of extrudates decreases with increasing shear stress. Fibers were spun from the samples having ηinh = 9.2 and 3.0 dL/g. The initial modulus and tenacity to break for 75HBA/25HNA fibers spun at sufficiently high shear stress to produce smooth filaments are significantly lower than the values we previously reported for fibers of the 58HBA/42HNA copolyester. Moreover, the optimum properties are obtained at relatively low spin-draw ratios. The 75HBA/25HNA polyester also exhibits a yield stress which decreases with increasing temperature. This observation indicates the presence of crystallities at the test temperatures. We believe that the higher content of HBA in the present copolymer gives rise to crystallization of HBA blocks in the thread line and that defects are introduced at higher spin-draw ratios which cause the mechanical properties to become worse.

A comparison of water sorption and diffusion behavior in 2 mil, as-received, Kapton1 film, and in otherwise identical but hygrothermally aged samples, suggests chemical differences between the samples. These differences can be related to known polyimide chemistry and the specific history encountered by the samples. Although the sorption isotherms are similar for an as-received 0.3 mil sample studied earlier and for the as-received 2 mil samples studied here, the diffusion coefficient of water in the as-received 2 mil sample is approximately 300% larger than in the as-received 0.3 mil sample. This large effect is believed to be related to the presence of small, paracrystalline aggregates with large aspect ratios. Differences in orientation measured by birefringence for the two samples suggest that the barrier properties of Kapton® are strongly affected by the detailed morphological organization of the ordered aggregates. Comparison of the sorption isotherms for the as-received and hygrothermally aged 2-mil films suggests a significant increase in the hydrophillic nature of the aged film. This change is consistent with an apparent chemical reaction between water and uncyclized amic acid residues in the film. The tendency for water to cluster in as-received Kapton® is essentially eliminated by the chemical modification associated with hygrothermal aging. The hygrothermal aging produces a dramatic reduction in the water vapor diffusion coefficient at low vapor activities but a rather modest change at high activities.

The rheological behavior of the thermotropic liquid crystal copolyesters composed of p-hydroxybenzoic acid and 2-hydroxy-6-naphthoic acid (indicated as HBA/HNA) is investigated for three different compositions: 75:25, 58:42, 30:70 (in mol%). The inherent viscosities are 9.2, 5.1, and 7.8 dl/g, respectively. Yield stress is observed for all three samples. This indicates the existence of crystallites in the melt which may be related to the shear thinning viscosity at low shear stress. Melt fracture, and a die swell ratio which increases with shear rate, are also observed at higher temperatures and at low shear stress for the two copolyesters having compositions 75:25 and 30:70. We have also estimated for 30HBA/70HNA at 335°C the entrance pressure loss, Δpent, and ΔPent/δw, where δw is the shear stress at the capillary wall. The large value of ΔPent/δw suggest that HBA/HNA is a highly elastic polymeric material. It is found that both ΔPent and ΔPent/δw increase with shear rate. However, the high elasticity does not account for the disappearance of melt fracture and contraction of die swell at high shear stress. This abnormal phenomenon is ascribed to the formation of a network of crystallites caused by blocky regions in the copolymer.

Sorption kinetics and equilibria as well as permeabilities and diffusion time lags for CO2 in Kapton polyimide film have been studied at temperatures from 35 to 55°C and pressures up to 0.78 atm. The sorption/desorption cycles indicate that the diffusivity of CO2 increases with increasing local penetrant concentration in the polymer. Both the permeability and time lag decrease with increasing upstream CO2 pressure. All of these results are described well by theoretical expression based on the dual-mode theory of sorption and transport in glassy polymers.