Point Defects in Mesophases: A Comparison Between Dilatometric and Small Angle X-Ray Scattering Studies

Abstract Small angle X-ray scattering (SAXS) studies have been performed in the columnar hexagonal and nematic mesophases of a 1,3-diacylaminobenzene. In both mesophases the molecules are self-assembled into columns by hydrogen bonds. The SAXS experiments confirm the existence of point defects in both phases. The generic π defect is the point where a single molecule is linked to three distinct half columns. In the hexagonal columnar phase single defects are progressively replaced by pairs of π defects of opposite orientations as temperature increases and the nematic phase contains only pairs of π defects. The comparison of SAXS and dilatometric experiments provides the structure factor, the volume and the concentration of each kind of defect.