ABSTRACT:Polysiloxanes containing acetoy group as a mesogenic terminal substituent were synthesized and the effects of acetoyl group on liquid crystalline properties and structures were investigated. The poly[{w-{4-(4-(acetoyl)phenoxy carbonyl)phenoxy}}alkyl methyl siloxanes] with different spacer lengths indicate smectic phases in the temperature range between glass transition (Tg) and isotropic phase transition (T;). Smectic A (SA) phase was observed in each polymer, and additional smectic phase appeared under the SA phase as spacer lengths increased. The higher ordered smectic phase could be assigned to smectic E-like phase from the X-ray scattering results. The T;'s, enthalpy and entropy changes of the polymers exhibited clearly odd-even effects.KEY WORDS Side Chain Liquid Crystalline Polymer / Polysiloxane / Acetoy Group / Smectic A / Smectic E / Odd-Even Effect /
Melt growth of Mg 2 Si was conducted using the vertical Bridgman growth method. Because magnesium is highly reactive at the growth temperature (1358 K), crucible materials were chosen to avoid chemical reactions and sticking between the crucibles, the molten Mg 2 Si and magnesium vapor. Crucibles made of alumina, pyrolytic boron nitride (pBN), and hexagonal boron nitride (hBN) were examined. The use of a pBN crucible enabled in the suppression of chemical reactions involving molten Mg 2 Si and vaporized magnesium at elevated growth temperatures, resulting in no sticking of the grown crystal to the inner wall of the crucible. While the measured conductivity for samples grown using an alumina crucible was n-type for all of the temperatures that were investigated, the samples that were grown using a pBN crucible exhibited p-type conductivity. This correlates closely with unintentional boron incorporation during the growth process.
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