X-Ray investigations in low-molecular-weight glassy mesophases

Abstract

Pure low-molecular-weight mesogenic compounds as well as mesogenic mixtures, able to form glass phases above room temperature, have been investigated by microscopy, calorimetry and X-ray scattering. Indications for two types of short-range order (SRO) in the glassy state have been found. Diffuse low-angle scattering maxima correspond to the formation of cybotactic groups in nematic phases. Meridional scattering maxima up to fourth or fifth order can be interpreted as due to separately existing one-dimensional strings of molecules. The splitting of equatorial reflections suggests freezing of rotational motion and can be interpreted in terms of nematic biaxial phases. This interpretation is supported by conoscopic observations. Investigations at higher temperatures show that the variety and intensity of reflections in the fluid nematic phase is reduced.