Department of Chemical Industry, Faculty of Basic Sciences, Technical and Vocational University, Tehran, I.R. IRAN
The phase transition of pentiloxcycyano biphenyl (5OCB), heptiloxycyano biphenyl (7OCB) liquid liquid crystal and the different mixtures of binary mixture of 7OCB-5OCB was studied to behavior of phase diagram by using differential scanning calorimetry (DSC). For 5OCB and 7OCB the crystal phase (C) to the nematic phase (N) phase transition temperature of was observed at temperatures 321 and 327 K, respectively, Whereas, in the binary mixture, the C to N phase transition temperature has decreased compared to each of the pure components, the highest decrease in phase transition temperature was observed in the 40% of mole furcation 7OCB liquid crystal. Additional functions in the binary mixture 7OCB-5OCB system were also investigated using regular solutions. The value of excess function such as Gibbs and enthalpy excess was to predict the behavior of the binary mixture with a slight deviation from the ideal state.