Critical phenomena in {bromobenzene + 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide} binary solution

• Coexistence curve, heat capacity and turbidity measurements were performed.
• RTIL solution showed 3D-Ising criticality.
• Universal critical amplitude ratios were testified.
• Asymmetric behavior of the diameter of coexistence curve was discussed.

The liquid-liquid coexistence curve for binary solution {bromobenzene + 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C6mim][NTf2])} has been measured in both critical and non-critical regions. The isobaric heat capacities per unit volume were measured in one-phase and two-phase regions. Moreover, the turbidity measurements were also performed in the near-critical one-phase region. From the liquid-liquid equilibrium, heat capacity and turbidity data collected in the critical region, the critical exponents α, β, γ and ν were obtained and shown to be consistent with those predicted for the 3D-Ising universality class. The universal critical amplitude ratios RB and X have been calculated and shown to reasonably coincide with the theoretical predicted values. The asymmetric behavior of the diameter of the coexistence curve was well described by the complete scaling theory, provided that the heat capacity related term was considered. Moreover, the coulombic criticality of the studied system was indicated by the small values of RPM reduced critical density and critical temperature.