Visual and acoustic investigation of the critical behavior of mixtures of CO₂ with a perfluorinated polyether

A simple acoustic method was used to investigate the critical behavior of mixtures of CO₂ + Krytox, a commercially available perfluoropolyether. A visual acoustic high-pressure cell recently developed was used. The cell was specially designed to include two piezoelectric transducers and two sapphire windows that make this cell well suited to investigate critical behavior of mixtures, using simultaneously the acoustic technique and the direct visual inspection of the critical opalescence. Measurements of the critical temperature T_c and pressure p_c of the binary mixture of xCO₂ + (1 - x)Krytox were performed restricted to the region richer in carbon dioxide, in the CO₂ mass fraction range 1-0.9636. Comparison of visual and acoustic data enabled the evaluation of the applicability of the acoustic technique to study the critical behavior of mixtures of CO₂ with low polydispersity polymeric material.