Liquid-Liquid Equilibrium of Aqueous Two-Phase Systems Formed by Nonionic Surfactants (Triton X-100, Triton X-165, or Triton X-305), Salts (NaNO3 or KNO3), and Water at Different Temperatures

Liquid-liquid equilibrium data for aqueous two-phase systems (ATPSs) formed by nonionic surfactants (Triton X-100, Triton X-165, or Triton X-305), inorganic salts (NaNO3 or KNO3), and water were obtained at 298.2, 313.2, or 328.2 K. For all the ATPSs studied, the upper phase was rich in surfactant, while the lower phase was rich in salt. The biphasic region increased with increasing temperature, which was associated with the reduced hydration of the hydrophilic portion of the surfactant micelles at higher temperatures. The cation K+ induced phase segregation more efficiently than the cation Na+, unlike the results usually reported in the literature for systems formed by polymers and salts based on the same cations. This result showed the dependence of the cation effect on the properties of the other component forming the system. The potential of phase segregation among the different surfactants was in the order Triton X-305 > Triton X-165 > Triton X-100, which was determined by the effect of molar mass overcoming the effect of hydrophobicity of the surfactant to determine the immiscibility region of the ATPS. The consistency of the equilibrium data was confirmed using the Bancroft and Othmer-Tobias correlations.