Optical microscopy, DSC, and X-ray diffraction studies on octyl and decyl members of the homologous series 4(4'-n-alkoxybenzoyloxy)phenyl azo-4"-isoamyloxy benzene

Octyl and decyl members of the homologous series 4(4'-n-Alkoxybenzoyloxy)phenyl azo-4"-isoamyloxy benzene have been studied by optical microscopy, DSC and X-ray diffraction techniques. Transition temperatures of the compounds are determined by observing texture by a polarizing microscope while transition enthalpies and entropies are determined by DSC studies. X-ray diffraction photographs of magnetically aligned samples indicate that the octyl member has cybotactic nematic phase while decyl member has cybotactic nematic and monotropic smectic A phase. X-ray photographs are analyzed to calculate intermolecular distance, apparent molecular length in nematics, layer spacing in smectics and orientational order parameters ( and ). Temperature dependence of these parameters has been discussed. Values of and are found to be consistent with Maier-Soupe theoretical values. Lengths of the molecules (L) in most extended conformation are found to be greater than the apparent molecular lengths in nematic phase which suggest that the molecules are tilted in the plane of cybotactic groups. Calculated tilt angles are found to be in between 41.8° to 43.3°.