Coexistence curves of ionic liquid in oil microemulsions of {[bmim][BF4]Â +Â T-X100Â +Â cyclohexane} with various molar ratio of [bmim][BF4] to T-X100 in the critical region

► The liquid-liquid coexistence curves of the ionic liquid microemulsion were determined in the critical region. ► The experimental results were analyzed to determine the critical exponent β and the critical amplitude B, and the anomalies of the diameters for different choices of order parameters. ► The IL microemulsions critical behavior belonged to the 3D-Ising universality class in a region sufficiently closed to the critical temperature.