Asymmetric Criticality Of Binary Solutions Containing [C_nmim][BF₄] Ionic Liquid And Alkanol

The critical mole fractions xc and the critical temperatures Tc of four ionic solutions {1-butyl-3-methylimidazolium tetrafluoroborate([C4mim][BF4]) + tert-butanol}, {[C4mim][BF4] + 1,2-butanediol}, {1-hexyl-3-methylimidazolium tetrafluoroborate([C6mim][BF4]) + 2-propanol} and {1-octyl-3-methylimidazolium tetrafluoroborate([C8mim][BF4]) + 2-pentanol} were determined by the criterion of “equal volume” near the phase separation points. The values of refractive indexes n were measured for each of coexisting phases at various temperatures to obtain the(T, n) coexistence curves. Then, the(T, x) coexistence curves were obtained from(T, n) coexistence curves by the “Standard Curve” method, which were further converted to(T, ?)、(T, ??) and(T, ??x) coexistence curves. The critical amplitudes Z0?B, Z1?B and critical exponents β were deduced from the liquid-liquid equilibrium data of the studied systems in the critical regions, and it was found that the critical exponent β coincided well with that predicted for 3D-Ising universality class.Isobaric heat capacities per unit volume were also measured in both critical and non-critical regions for {[C6mim][BF4] + 2-propanol} using Micro DSC III. Both the critical exponent α and the amplitude ratio A/ A? ?were deduced and showed good agreements with the theoretical ones. The asymmetric behaviors of the diameter of the coexistence curves were analyzed by the complete scaling theory, which indicated that the heat capacity related term plays an important role in describing the asymmetric behavior of the coexistence curves. This study is of great significance for understanding and application of the special properties of ionic solutions caused by the critical fluctuations.