Liquid–liquid phase equilibria of ionic liquid solutions in the critical region: 1-Methyl-3-octylimidazolium tetrafluoroborate with 1-pentanol or 1-hexanol

• Liquid–liquid equilibria of binary RTIL/alcohol solutions were measured.
• Asymmetry of the coexistence curves was analyzed.
• Critical behaviors of RTIL/alcohol solutions were investigated.
• Dependences of critical parameters on the solvent's permittivity were studied.

The liquid–liquid coexistence curves for the binary solutions of the room temperature ionic liquid (RTIL) 1-methyl-3-octylimidazolium tetrafluoroborate ([C8mim][BF4]) in 1-pentanol and 1-hexanol were measured in the critical region. The critical exponent β and the critical amplitude B were deduced and the former was found to be consistent with the 3D-Ising value. The complete scaling theory was applied to describe the asymmetry of the diameters of the coexistence curves. Moreover, the dependences of the critical temperature, the critical mole fraction, the reduced critical temperature and the reduced critical density on the permittivity of alcohol for a series of binary solutions of RTIL in alcohols were discussed.