Exploration of a quadruple critical point in a quaternary liquid mixture

Abstract

We report the preliminary findings concerning the nature of a quadruple critical point that evolves when two independent double critical points merge in a thermodynamic field space. This special critical point is realized in a quasibinary mixture of 3-methylpyridine, water, heavy water, and KI. The critical behavior of osmotic susceptibility was deduced from the scattered intensity measurements at 90°. Our results suggest that the nature of a quadruple critical point is similar to that of a normal double critical point. In addition, we find that the significance of the leading correction-to-scaling term is markedly increased as a result of the presence of the salt (KI) in the system.