Small Angle X-Ray Diffraction Studies on the Homologous Series of Mesogenic 4-(trans-4′-n-Alkylcyclohexyl)Isothiocyanatobenzenes

Abstract

The compounds of the series (nCHBT in short, n=4–9) show only nematic phase with supercooling effect. 4CHBT and 5CHBT show monotropic transition. X-ray diffraction studies of magnetically oriented samples have been done in the entire nematic range which indicate that all the members possess ordinary nematic phase. The average intermolecular distance is found to be ∼5.1Å for all of them. The apparent molecular length, 1 varies from 22.3A for 4CHBT to 29.3Å for 9CHBT at 0.98T_NI. Temperature dependence of these parameters has been discussed. Average values of apparent molecular lengths in their nematic range are found to be ∼1.1 times of their respective molecular model lengths indicating the presence of bimolecular association. The orientational order parameters, <P₂> were found to be slightly higher than Maier-Saupe theoretical values and lower than the values obtained from refractive index studies; whereas <P₄> values were found to be comparable with Maier-Saupe values. The results have been discussed in relation to three other similar homologous series.

Key Words:

• nematic
• X-ray diffraction
• order parameters
• molecular association