Order parameters of some homologue cybotactic nematics from X-ray diffraction measurements

Abstract

The hexyl, octyl and decyl members of the homologous series bis-(4′-n-alkoxybenzal)-2-chloro-1,4-phenylinediamine have been studied by X-ray diffraction at different temperatures under various magnetic fields. The intermolecular distance the tilt angle, the orientational distribution function and the orientational order parameters have been calculated. The intermolecular distance, tilt angle and the ‘degree of ordering’ is found to depend on magnetic field strength. Order parameters ⟨P ₂⟩ and ⟨P ₄⟩ are found to be slightly lower for BHeCP, more or less equal for BOCP, and slightly higher for BDeCP than those predicted by mean field theory. ⟨P ₂⟩ values for BHeCP snd BOCP agree well with the values obtained from refractive-index measurements, but for BDeCP our ⟨P ₂⟩ values are higher.

Key Words:

• Order parameters
• X-ray diffraction
• nematics