Investigation Of The Critical Phenomena In Ionic Solutions Containing "C_nmim"~+

The critical compositions xc and the critical temperatures Tc of three ionic solutions{x 1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim][PF6])+(1-x) ethanol},{x 1-octyl-3-methylimidazolium hexafluorophosphate ([C8mim][PF6])+(1-x) 1-propanol} and{x [C8mim][PF6]+(1-x) 2-propanol} were determined by the technique of the "equal volumes". The precise coexistence curves were performed by measuring the temperature dependence of the refractive index in the two phases of above three ionic solutions with the critical composition. The coexistence curves of (T—n) were converted to the coexistence curves of (T—x) which were further converted to the coexistence curves of (T—Φ). Where x andΦare mole fraction and volume fraction, respectively. The critical exponentsβ, the critical amplitudes B and the amplitudes of the Wegner correction coefficients B1 were deduced from three types of the coexistence curves. Near the critical points, the critical exponentsβfor the three ionic solutions are consistent with the universal 3D-Ising value. It was found that the crossover exists from the 3D-Ising behavior near the critical points to the mean field behavior far way the critical region for the three ionic solutions and is well described by the two-parameter crossover model proposed by Anisimov and Sengers et al.The asymmetry of the coexistence curves were discussed in terms of the complete scaling theory for seven ionic solutions{x[C4mim][PF6]+(1-x) ethanol},{ x [C8mim][PF6]+(1-x) 1-propanol},{x[C8mim][PF6]+(1-x) 2-propanol},{x1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim][BF4])+(1-x) 1-propanol},{x[C4mim][BF4]+(1-x) 2-propanol},{x [C4mim][BF4]+(1-x) 1,3-propanediol} and{x[C4mim][BF4]+(1-x) 1,4-butanediol} under the condition of incompressible limit. The asymmetry coefficients are consistent with the prediction of incompressible complete scaling theory.