NON-LINEAR DIELECTRIC EFFECT IN BENZONITRILE AND NITROETHANE SOLUTIONS

The nonlinear dielectric effect NDE ΔεE-2 for the binary systems benzonitrile in hexane and carbon tetrachloride as well as nitroethene in cyclohexane and benzene has been measured in critical mixtures.Molar correlation factors Rp and Rs have been calculated in dependence on temperature and concentration. It has been found that the appearance of positive values of NDE, i.e. negative Rs, is due to fluctuation phenomena and the effects are proportional to (T/Tc - 1)ξ. The critical exponents ξ are close to 0.44 and 0.36 for the benzonitrile and nitroethane critical solutions. The difference in the critical exponents corresponds to deviations from linear dependence on T of the ε and molar volume excess in both systems studied. The linear dependence of log(1 - Rs) versus log(T/Tc - 1) allows us to estimate Tc for benzonitrilecyclohexane and benzonitrile-carbon tetrachloride solutions. The influence of electrostriction, nonuniformity of electric field and gravity effect on the NDE are discussed. © 1979.