Phase equilibrium in aqueous two-phase systems containing poly(vinylpyrrolidone) and sodium citrate at different temperatures—Experimental and modeling

The phase diagrams and compositions of coexisting phases have been determined for aqueous two-phase systems containing poly(vinylpyrrolidone) (PVP) and sodium citrate at various temperatures of 298.15, 308.15, 318.15 and 328.15 K. The effect of temperature on the salting-out effect of poly(vinylpyrrolidone) by sodium citrate has been studied. It was found that, an increasing in temperature caused the expansion of two-phase region. Increasing temperature also increases the concentration of PVP in the PVP-rich phase, while the salt-rich phase will be somewhat mole diluted. Furthermore, it was found that, as temperature is increased, this aqueous two-phase system exhibits a phase inversion. Specifically, the PVP-rich phase – which at low temperatures is the less dense top phase – becomes the lower phase at elevated temperatures. The results have been discussed on the basis of the effect of temperature on the hydrophobicity of the polymer. Furthermore, the Wilson model has been used for the correlation of the experimental liquid–liquid equilibrium data.