Deuterium nuclear magnetic resonance study of the orientational order in the nematic phase of 4-n-pentyloxy-4′-cyanobiphenyl. Tests of the Emsley–Luckhurst–Stockley theory and of the Haller extrapolation

Abstract

The deuterium NMR spectrum of 4-([²H₁₁]pentyloxy)-4′-cyano[3,5-²H₂]biphenyl has been measured as a function of temperature within its nematic phase. The deuterium quadrupolar coupling constants and hydrogen–deuterium dipolar coupling constant allow determination of the second-rank orientational order parameters for axes set in the rigid sub-units of the molecule. Such detailed information is of particular value in testing molecular theories of nematogens composed of flexible molecules, especially as analogous data are available for other members of the homologous series of 4-n-alkyloxy-4′-cyanobiphenyls. The potential applications of our new results are illustrated by testing the Emsley–Luckhurst–Stockley theory as well as determining the parameters contained in it and also by exploring the validity of the Haller extrapolation.