Effects of Inorganic Salts on the Phase Separation of Partially Miscible Solutes

Partially miscible solutions with a lower critical solution temperature have promising applications in the field of physical chemistry. To better guide the utilization of these solutions in practice, we conduct an in-depth study about the phase separation behavior of the solution added with inorganic salts. The addition of the inorganic salts into the solution is found to consequently reduce the phase separation temperature. The variation of concentrations of inorganic salts does not notably affect the mass fraction of the separation. Moreover, the addition of inorganic salts in the solutions at lower mass fractions improves the separation mass fraction, while the addition of inorganic salts decreases the separation mass fraction at the mass fractions above 30%. It sheds light on selecting the proper mass fractions and inorganic salt concentrations. Furthermore, we explore the phase separation behavior of mixed solutions under different inorganic salt additions by means of a high-speed camera. The phase separation behavior under different inorganic salt systems shows a similar trend. However, calcium ions and Fe³⁺ ions in the solutions can greatly decrease the rate of droplet coalescence and result in an increase in phase separation. For better regulating the solutions with a lower critical solution temperature through inorganic salts, sodium chloride or potassium chloride is recommended with an appropriate concentration.