Search

Unique 2H-NMR spectral patterns can be obtained from biaxially ordered smectic E and G phases, where only one director of the phase is aligned by the magnetic field. Two effects on the shape of the deuterium spectral pattern are demonstrated: (1) The effect of a motionally induced asymmetry parameter in the time averaged deuterium quadrupole interaction, and (2) the effect when the principal z-axis of the time averaged interaction is not parallel to the aligned director. Spectral patterns for the SG phase of the compound 4-n-pentoxybenzylidene-4-n'-heptylaniline selectively deuterated on one of the aromatic rings (50.7-d4) were obtained for both unaligned and magneto-aligned samples. Both of these spectral patterns were consistent with that expected for an asymmetry parameter, n < 0.2. Spectral patterns in the SG phase of the compound 50.6 (24.7 wt.%) + 90.4-αd2-γd2 (75.3 wt.%) were studied showing a different behavior with respect to the spectral patterns obtained in 50.7. We believe that a shift in the orientation of the z principal axis relative to the sample c axis has occurred in this SG phase. Spectral patterns were also recorded for the SE phase in magneto-aligned samples of the mixture of compounds 4-cyano-4'-octyloxybiphenyl (80CB) with 50 wt.% 40.8-d4. These data also show a small asymmetry parameter but, in addition, a distribution in the orientation of the principal z-axis indicating that the time scale of the motion of the long molecular axis is in a regime where it is of the order of the 2H-NMR measurement. Models for the smectic E and G phases based on these observations are discussed.

We report on a variant of the reentrant phenomena whereby a chiral compound has been added to a liquid crystalline material to form the sequence of phases cholesteric smectic A cholesteric as the temperature is varied. We present here a phase diagram which shows the effects of different concentrations of chiral additive and describe an unusual texture which appears under a polarizing microscope in the vicinity of the transition from the smectic A phase to either the reentrant cholesteric or the cholesteric phases.

High information content liquid crystal displays (minimum 250 × 250 picture elements) operated in the fast update (TV) mode require the incorporation of an electronic switch into each picture element. α-Si:H(F)1 is a suitable material for the implementation of both two (diode) and three (TFT) terminal devices for matrix addressed LCDs. A simple analysis of α-Si TFTs shows that the low mobility of α-Si is an optimal match to the Ioff requirements. while competing technologies (CdSe, poly-Si) encounter difficulties. However. using 10μ channel lengths, the mobility of α-Si was considered insufficient to drive active matrix displays. We report an innovative α-Si TFT which achieves short channel length and high mobility. The DC and the transient response characteristics will be presented. Ring oscillators were designed using this characteristic. Computer simulations suggest that an eleven stage ring oscillator utilizing α-Si TFTs can operate at 2.2 MHz. These advances will allow us to overcome the limitations in device response which has thus far prevented α-Si from being used in driving and addressing active matrix displays.

X-ray diffraction patterns and observations under the polarizing microscope made on binary mixtures of 4-cyano-4'-n-hexyloxybiphenyl (60CB) and 4-cyano-4'-n-octyloxy-biphenyl (80CB) to which the chiral material 4''-(2-methylbutylphenyl)-4'-(2-methyl-butyl)-4-biphenylcarboxylate (CE2) has been added, have revealed the occurrence of a new variant of liquid crystalline reentrant polymorphism: isotropic-cholesteric (twisted nematic)-smectic A-smectic E-cholesteric (twisted nematic)-solid. X-ray measurements of the layer spacings in the smectic A phase of such samples and similar ones where chiral CE2 has been replaced by chiral 4-cyano-4'-(2-methyl)butylphenyl (CB-15) are found to be consistent with the predictions of a recent microscopic model of the reentrant phenomena whereby the formation of molecular association pairs is an important factor determining the occurrence of the reentrant phase.