Broadband dielectric study of liquid crystal 4- n-decyl-4′-cyanobiphenyl (10CB) dispersed with hydrophilic aerosil particles

Abstract

Real ( ε′) and imaginary ( ε″) parts of the complex dielectric permittivity ( ε ∗) of the liquid crystal 4- n-decyl-4′-cyanobiphenyl (10CB) dispersed with hydrophilic aerosils, were studied by means of broadband dielectric spectroscopy. In bulk 10CB, which has a direct transition from isotropic to a smectic-A phase, there exists one relaxation process for the parallel orientation of the director to the probing field and another fast relaxation process in the perpendicular orientation. All molecular relaxation processes in 10CB have an Arrhenius-like temperature dependence. The aerosil particles in the LC–aerosil system attach to each other via hydrogen bonding and form a three-dimensional interconnecting aerosil network, thus dividing the LC phase into small domains. 10CB dispersed with different concentrations of hydrophilic aerosils lead to the emergence of a slow relaxation process that was stronger for higher concentration of aerosils. The slow process in the LC–hydrophilic aerosil system is attributed to the relaxation of the molecules that are homeotropically aligned close to the surfaces of the aerosil particles. The temperature dependence of the relaxation times of this process is quite weak.