Highly precise (liquid+liquid) equilibrium and heat capacity measurements near the critical point for [Bmim][BF4]+1H, 1H, 2H, 2H perfluoroctanol

[Display omitted] •Highly precise liquid–liquid curves for [Bmim][BF4]+perfluoroctanol are reported.•Critical behavior of heat capacity for the same system was also characterized.•In contrast to previous results, no coulombic/solvophobic crossover for coexistence curve diameter was found.•The system criticality shows characteristics both solvophobic and coulombic. Liquid+liquid equilibrium of the system [Bmim][BF4]+1H, 1H, 2H, 2H perfluoroctanol using a highly precise methodology based on refractive index measurements was experimentally determined. In addition, isobaric heat capacity near the critical point was obtained. The performance of the new refractive index set-up was successfully checked against the coexistence curve of the system dimethyl carbonate+decane, since highly accurate data are available in the literature. The choice of [Bmim][BF4]+1H, 1H, 2H, 2H perfluoroctanol was motivated by a previous experimental work, whose results suggest that this system could present characteristics of both solvophobic and coulombic behavior, which are the two categories to which an ionic system can belong. Although this was previously observed for other ionic systems, this mixture presented a very striking feature: the diameter of the coexistence curve seemed to change its criticality in the studied temperature range, from solvophobic far away to coulombic close to the critical point. The results of this work reveal that, in fact, [Bmim][BF4]+1H, 1H, 2H, 2H perfluoroctanol presents characteristics of both solvophobic and coulombic criticality, but no evidence of the observed crossover over the experimental temperature range has been found.