X-Ray Diffraction by Cybotactic Nematics

Abstract

Several magnetically aligned liquid-crystal monodomains yielded x-ray diffraction photographs containing four intense maxima about the direct beam characteristic of cybotactic nematics. In the case of p-alkoxy benzoic acids, such maxima appear, both, when a smectic-C phase forms at lower temperatures and when the nematic transforms to the crystalline phase directly. The intensity distribution in reciprocal space for azoxybenzene and BOCP was found to lie along two interpenetrating rings whose common diameter is normal to the aligning magnetic field and for p-n-alkoxybenzoic acids along outwardly curving arcs. Four similarly intense maxima recorded in x-ray diffraction photographs of a thermotropic liquid-crystalline polymer were found to be part of two parallel rings lying in planes normal to the polymer axis.