Effect of temperature on the liquid-liquid equilibrium of the ternary system water + pluronic10R5 + ammonium thiosulfate

Aqueous two-phase system (ATPS) have been investigated as alternative system for liquid-liquid extraction. Many ATPS phase diagrams for triblock copolymers (PPG-PPO-PPG) have been reported, but few information is available regarding liquid-liquid equilibrium data for inverted copolymers (PPO-PPG-PPO), denote pluronic10R5. Self-aggregated structures formed by triblock copolymers have range of applications, extending from the cosmetic field to the nanotechnology1. In the present work, the phase diagrams for pluronic10R5 + ammonium thiossulfate + H2O were experimentally determined at 283.2, 298.2, and 313.2 K. The statistic treatment was introduced by the gravimetric method2. The method is the following: initially a curve representing the binodal is obtained through a turbidimetric titration. A point is selected in the phase diagram, containing a certain concentration and the components required are weighed and mixed thoroughly. The tubes are left in thermostatic bath until complete separation of phase. Posteriorly, the bottom phase is collected and weighed. With the mathematical treatment the compositions of the top and bottom phases are obtained. The Fig. 1 shows that the increase in temperature enlarges the area of the phase diagram, indicating the enthalpic contribution to the formation of the biphasic system. This is indication that the phase-separation process is endothermic and is entropically directed as proposed by da Silva and Loh3.