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

• Published in: Phase transitions 2000-01, Vol.71 (1), p.1-12
• Main Authors: Sarkar, Parimal, Sarkar, Pranab K., Paul, Sukla, Mandal, Pradip
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Liquid crystals; Order parameters; Orientational order of liquid crystals; electric and magnetic field effects on order; Phenyl benzoates; Physics; Skewed cybotactic nematic; Structure of solids and liquids; crystallography; X-ray diffraction
• ISSN: 0141-1594; 1029-0338
• DOI: 10.1080/01411590008228974

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.