Optical and thermodynamic studies of binary mixtures of nematic liquid crystals from homologous members of alkyloxybenzoic acid

901-907Transition temperature (Tp), transition enthalpy (ΔH) and transition entropy (ΔS) for the binary mixtures of heptyloxybenzoic acid (HOBA) and decy loxybenzoic acid (DOBA) in different mole ratios have been determined using differential scanning calorimeter (DSC). The phase diagrams for the heating and cooling cycles have been drawn which show the eutectic composition of DOB A- HOBA binary system in the ratio of 48:52 mole per cent. A wide range smectic C(SmC) phase (range ~40oC) followed by the nematic (N) phase (range ~34oC) has been observed around the eutectic composition of DOBA-HOBA binary system. SmC-N and N-I (isotropic) transition temperatures (TC-N and TN-1) have been round to vary, almost linearly, with the mole fraction of components, indicating the system as an ideal mixture. For the eutectic cumposition of the HOBA-DOBA system, it has been possible to bring down SmC phase to 60oC with enhanced temperature range, whereas no member of the alkyloxybenzoic acid series has SmC phase below 92°C.