The liquid-liquid coexistence curves of {x 1-octyl-3-methylimidazolium hexafluorophosphate + (1−x) 1-butanol} and {x 1-octyl-3-methylimidazolium hexafluorophosphate + (1−x) 2-butanol} in the critical region Cui, Z.; Cai, D.; Fan, D.; Chen, Z.; Shen, W.; Fluid Phase Equilibria 2013, 348, 52-59