Nonlinear dielectric studies of intermolecular interactions and structure of 4-heptyl-4-cyano-biphenyl in benzene

Abstract

The energies of intermolecular interactions in benzene solutions of 4-heptyl-4′-cyanobiphenyl (7CB) in concentration range 0–0.4 mole fraction have been determined from the experimental data of linear and nonlinear electric polarisation. The theory of the nonlinear dielectric effect for associated solutions is discussed. To achieve the agreement between theoretical calculations and experimental data the Flory athermal model of association was used. The results show that the dimerisation, so important in very diluted solutions, is only the firsdt step to a more complex process of molecular association. The low polar clusters with even number of molecules (mainly dimers and tetramers) are the dominant. Beside the distinctly preferred antiparallel orientation, the concentrations of highly polar, chain multimers are also significant. The possible reasons why the model does not work for concentrated solutions are also discussed.