Liquid–liquid phase equilibria of binary solutions of the room temperature ionic liquid (RTIL) 1-methyl-3-octylimidazolium tetrafluoroborate ([C8mim][BF4]) with 1-heptanol or 2-pentanol were measured. The critical exponents β obtained from the liquid–liquid equilibrium data in the critical region were consistent with the 3D-Ising value, which confirmed the 3D-Ising criticality of the investigated binary ionic solutions. The asymmetry of the diameters of the coexistence curves was analyzed by the complete scaling theory, indicating a significant contribution of the heat capacity related term. The RPM (restricted primitive model)-rescaled critical parameters were calculated, which showed dual characters of both solvophobic and coulombic criticalities of the studied binary ionic solutions.
