X-ray scattering studies on two nematogenic p-alkylphenyl-2-chloro-4-(p-alkylbenzoyloxy)-benzoates and their mixtures

Abstract

The compounds, p-n-pentylphenyl-2-chloro-4-(p-n-pentylbenzoyloxy)-benzoate and p-n-octyiphenyl-2-chloro-4-(p-n-heptylbenzoyloxy)-benzoate show a nematic phase with supercooling effect below room temperature. Marble textures are observed under a crossed polarizing microscope; however, near the N-I transition schlieren textures are observed. Mixtures of three different mole fractions of them form a nematic phase at well below room temperature. Small-angle X-ray scattering studies on all the magnetically aligned samples have been done in their entire mesomorphic ranges. X-ray diffraction patterns show that in each case the mesophases skewed cybotactic nematic. The average intermolecular distance is found to be ∼ 5.10 Å and the interplanar spacing of cybotactic groups is found to be less than the stereo model length of the molecules in all trans-configurations. Temperature dependence of these parameters is discussed. Orientational order parameters, 〈P ₂〉 and 〈P ₄〉. for the Pure compounds and their eutectic mixture are calculated and compared with Maier-Saupe theoretical values. 〈P ₂〉 and 〈P ₄〉 values of the mixture are found to lie between those of the individual components.

Key Words:

• Phenyl benzoates
• X-ray diffraction
• Skewed cybotactic nematic
• Order parameters