Experimental Study On Complete Scaling Of Binary Fluid Mixtures

The liquid-liquid coexistences of temperature vs. refractive index (T-n), temperature vs. mole fraction (T-x), and temperature vs. volume fraction(T-?) for dimethyl carbonate+ alkanes (nonane, decane, dodecane, tetradecane, hexadecane and octadecane) have been determined within 10 K from the critical temperatures. The critical amplitudes B and the critical exponents?have been deduced from the coexistence curves. The results have also been analyzed to determine the Wegner-correction terms and to examine the diameters of the coexistence curves. The crossover behavior of coexistence curves (T-x) was discussed according to the theory proposed by Anisimov and Sengers. The asymmetry of the coexistence curves for systems of nitrobenzene+alkanes, benzonitrile+alkanes, dimethyl carbonate+alkanes and dimethyl adipate+alkanes was studied in terms of the complete scaling theory proposed by G. Perez-Sanchez under the condition of incomplete limit and neglecting the contribution of the heat capacity and the excess volume. The results indicate that the solute/solvent reduced molar volume ratio is a better character quantity than the chain length of alkane for describing the asymmetry of the coexistence curve. However, the asymmetry coefficient is inconsistent with the prediction of the complete scaling theory.The isobaric heat capacities per unit volume for the critical mixtures of dimethyl carbonate +alkanes (nonane, decane and dodecane) and dimethyl adipate+alkanes (hexane, heptane, octane and nonane) have been measured in the wider temperature ranges of both near and far away from their upper critical consolute points by means of a differential scanning calorimeter. The exponents and amplitudes that characterize the heat capacity anomaly were obtained from the measured experimental data both in one-phase and two phase regions, which were in accord with the theoretical predictions. The critical amplitudes of the correlation length were calculated by using the critical amplitudes of the heat capacity and the two-scale-factor universal ratio and found to be in agreement with the experimental results. The universality of the ratio relating the critical amplitude of the heat capacity, the amplitude of the first correction to scaling term, and the critical background of the heat capacity was tested, and its value was found to be in agreement with the experimental results, but significantly smaller than the theoretical prediction, indicating the corresponding theory should be further improved. The experimental data have also been analyzed to investigate the crossover behavior of the heat capacity. It was found that the value of the effective critical exponent of the heat capacity decreased from 0.11 to almost zero as the distance from the critical point increased, indicating a critical crossover from the 3D-Ising to the mean-field. Furthermore, the experimental data of the heat capacity were used to further study the asymmetry of the coexistence curves for systems of nitrobenzene+alkanes, benzonitrile+alkanes, dimethyl carbonate+alkanes and dimethyl adipate+alkanes in terms of the complete scaling theory proposed by G. Perez-Sanchez under the condition of incomplete limit and neglecting the excess volume. The results validated the relationship between the asymmetry of the coexistence curve and the solute/solvent reduced molar volume ratio described by the incompressible complete scaling theory, indicating the heat capacity makes important contribution to the asymmetry behavior of the coexistence curve.Densities measurements at a certain temperature range have been determined for the binary systems of dimethyl adipate+alkanes (heptane and octane) over the entire range of composition. The results were used to calculate the excess molar volumes and the excess isobaric thermal expansivities. The dependences of the excess molar volumes on both temperature and composition were analyzed in terms of the natures of the two pure components and the molecular interactions between unlike molecules. In addition, the effect of the excess molar volume on the asymmetry behavior of the coexistence curve was evaluated in terms of the complete scaling theory and found to be negligible.