Density fluctuations in aqueous solution of ionic liquid with lower critical solution temperature: Mixture of tetrabutylphosphonium trifluoroacetate and water

Aqueous solutions of tetrabutylphosphonium trifluoroacetate ( [P-4444]CF3 COO) exhibit a LCST-type phase transition with the critical point near 0.025 in mole fraction of [P-4444]CF3 COO at T=302 K. The phase behavior of [P-4444]CF3 COO-water mixtures was investigated by evaluating their density fluctuations, which provide quantitative descriptions of the mixing states of the solutions. The concentration dependence of the density fluctuations was investigated at 293 and 301 K for the mixtures without distinguishing the components and for the individual components ( [P-4444]CF3 COO and water). A drastic change in the mixing state was observed for the solution when the critical point was approached. (C) 2015 Elsevier B.V. All rights reserved.