Order parameter and packing studies in nematic and smectic A phases by xhyphen;ray diffraction

摘要

Xhyphen;ray diffraction measurements have been made on the nematic phase of T15 (4hyphen;cyanohyphen;4rsquo;hyphen;nhyphen;pentylhyphen;phyphen;terphenyl), as well as on the nematic and smectic A phases of RNO2lsqb;4rsquo;hyphen;nitrophenylhyphen;4hyphen;(4rsquo;hyphen;nhyphen;hexyloxyhyphen;benzoyloxy)hyphen;cinnamatersqb;. The xhyphen;ray equipment used allows comparably high resolution measurements of liquid crystals. The inner reflexes show that both compounds possess a bilayer structure supposed as overlapping of polar cyano or nitro group of one molecule and the phenyl ring of the neighboring molecule. The molecular orientational distribution functionfthinsp;(bgr;) has been calculated on the basis of intensity simulations of the outer reflexes. The orientational order parameterP2(costhinsp;bgr;),P4(costhinsp;bgr;), lang;P2rang; and lang;P4rang; have been determined fromfthinsp;(bgr;). A strong decrease of lang;P2rang; and lang;P4rang; is observed at the smectic Andash;nematic phase transition temperature of RNO2.