Order parameter and packing studies in nematic and smectic A phases by x-ray diffraction

Publisher Website
Google Scholar
Abstract
X‐ray diffraction measurements have been made on the nematic phase of T15 (4‐cyano‐4’‐n‐pentyl‐p‐terphenyl), as well as on the nematic and smectic A phases of RNO2 [4’‐nitrophenyl‐4‐(4’‐n‐hexyloxy‐benzoyloxy)‐cinnamate]. The x‐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 function f (β) has been calculated on the basis of intensity simulations of the outer reflexes. The orientational order parameter P2(cos β), P4(cos β), 〈P2〉 and 〈P4〉 have been determined from f (β). A strong decrease of 〈P2〉 and 〈P4〉 is observed at the smectic A–nematic phase transition temperature of RNO2.