A5B6C7 type crystals are semiconductors – paraelectronics. I analysed this crystal structure and compared free methods of investigation.

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Ferroelectric liquid crystals (FLCs) are being investigated as alternatives to nematic liquid crystals in display applications due to their low power requirements and fast switching times. Commercial FLCs consist of a chiral dopant in an achiral smectic C (SmC) liquid crystal host. A bulk property that arises from the chiral nature of this mixture is a spontaneous polarization (PS), which depends on the polarization power of the chiral dopant (δp). The magnitude of δp reflects the ability of a dopant to induce a polarization in an achiral host. It has been proposed that the magnitude of δp can be enhanced by matching dopant and host structures, which may enhance the propagation of chiral perturbations from the dopant to the host. This is known as the chirality transfer feedback (CTF) model. Previous studies in the Lemieux lab featured 2H NMR to detect chiral perturbations exerted by a dopant on the liquid crystal host based on the observation of pairs of quadrupolar doublets in the 2H NMR spectra. In the work described herein, the contribution of chirality transfer feedback to the difference in quadrupolar splitting between pairs of quadrupolar doublets (ΔΔνQ) was assessed by 2H NMR spectroscopy. These experiments confirmed the results reported by Finden and Yuh by demonstrating the presence of chiral perturbations exerted by a diester substituted 6,6’-spirobiindandione dopant ((RS)-2.6-d4) on the achiral SmC host NCB76, and the absence of those perturbations using the diester substituted 5,5’-spirobiindandione analogue ((RS)-2.3-d4). Subsequent studies explored the effect of modifying the chiral topography of the 2,2’-spirobiindan-1,1’-dione core on the magnitude of δp. Both the 5,5’- and 6,6’-disubstituted cores were reduced to give the corresponding mono-carbonyl derivatives ((R)-3.4-d4 and (R)-3.8-d4), substituted with ether side-chains. Finally, ester side-chains were added to the 6,6’- mono-carbonyl derivative ((R)-3.9-d4) for comparison with previous experiments. The ferroelectric induction properties of these dopants were investigated in NCB76 at mole fractions ranging from xd = 0.03 – 0.10. The mono-carbonyl 5,5’- and 6,6’-diether dopants gave absolute polarization powers of 120 nC/cm2 and 123 nC/cm2 respectively, which are not significantly different. This suggests that a reduction in the chiral topography of the spirobiindandione core greatly affects the polarization power of the dopant and may reduce the contribution from chirality transfer to δp. This was confirmed by a measurement of the polarization power of the 6,6’-diester mono-carbonyl dopant (R)-3.9-d4 in NCB76, which gave a δp value of 117 nC/cm2. / Thesis (Master, Chemistry) -- Queen's University, 2008-07-11 15:10:53.56

Ferroelectric liquid crystals (FLCs) have been investigated as the basis for a new type of liquid crystal display because of their fast switching times. Commercial FLC materials are mixtures consisting of a small amount of chiral dopant in an achiral liquid crystal host with an isotropic-nematic-smectic A-smectic C (INAC) phase sequence, which is required to achieve proper alignment between glass slides with rubbed polyimide alignment layers. However, the layer contraction occurring at the SmA-SmC phase transition on cooling from isotropic liquid is a severe problem that leads to a buckling of the smectic layers and results in zigzag defects that drastically degrade the optical quality of FLC films. To solve this problem, we are focusing on a new class of liquid crystal molecules with minimal or no smectic layer shrinkage at the SmA-SmC transition which is referred to as ‘de Vries-like.’ Previous work in the Lemieux group has shown that combining structural elements promoting SmA and SmC phases in a single molecule increases de Vries-like behavior. Giesselmann et. al. suggest that a correlation exists between the temperature range of the SmA phase and de Vries-like behavior. In the study described herein, two homologous series of molecules with 2-phenylpyrimidine cores with siloxane-terminated side-chain (SmC promoting element) and a chloro-terminated side-chain (SmA promoting element)are synthesized and characterized by polarized optical microscopy, differential scanning calorimetry and small-angle X-ray diffraction (SAXS). The reduction factor R for series 1.13 from 0.36 to 0.46 and for series 1.14 from 0.47 to 0.54. Results show that, although there is some correlation between % layer contraction and SmA temperature range, it can be explained primarily by differences in tilt angle θ. When θ is taken into account in the R values, there is no correlation. Another aspect of the study described herein, two siloxane-terminated 2-phenylpyrimidine chiral dopants are synthesized and characterized by polarized optical microscopy, differential scanning calorimetry and small-angle X-ray diffraction (SAXS). / Thesis (Master, Chemistry) -- Queen's University, 2009-11-30 13:42:44.584

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The quartz microstructures and microfabrics in tectonites representing greenschist to granulite facies conditions are examined to assess the factors influencing their development. The c-axis patterns range from random distributions to small, great, and crossed circle girdles, and to c-axes maxima. The small circle girdles, the most common fabrics at all metamorphic grades, are oriented at 30(DEGREES)-40(DEGREES) and 50(DEGREES)-70(DEGREES) about the axes of shortening and extension, respectively. / The c-axis orientations of the recrystallized grains bear no relationship to those of the host grains suggesting that host control, though important initially, is commonly overridden by strain controls. / The style and magnitude of strain, and the metamorphic grade are the significant controlling factors in the microfabric development. Intracrystalline slip mechanisms are favoured for the origin of the c-axis preferred orientations. Apparent discrepancies between experimental and natural fabrics can be reconciled when symmetries of strain are considered.