1. Physico-chemical characterization of ATPS of Tween 20 + Water + (Na 2 SO 4 or Na 2 S 2 O 3 ) ternary mixtures in function of the temperature Antonio Blanco, Ana Gayol, Diego Gómez-Díaz, José M. Navaza Department of Chemical Engineering. ETSE. University of Santiago de Compostela. Galicia, Spain. Aqueous two-phase systems (ATPS) are formed by mixing by one polymer and one aquous solutions of salts. Present work analyses several physical properties (density, speed of sound, refractive index) of ternary systems using blends of polymer (Tween 20), Water and Salt (Na 2 SO 4, Na 2 S 2 O 3), were measured over the temperature range employed in this work (288.15 to 318.15) K and atmospheric pressure. Also, present study includes the analysis of the influence of composition and temperature upon the previously commented physical properties. The obtained behavior for density, for both systems (Tween 20 + Water + Na 2 SO 4 and Tween 20 + Water + Na 2 S 2 O 3 ) is similar obtaining an increase in the value of this physical property when the mixtures enriched in polymer. On the other hand, temperature produces a decrease in the value of density. Figure 1. Influence of mixture composition on density and speed of sound. Tween 20(1) + Water (2) + Na 2 S 2 O 3 (for 1.93% Na 2 S 2 O 3 :  density,  speed of sound ; Tween 20 (1)+ Water (2) + Na2SO4(39 for 1.56% Na 2 SO 4 : density,  speed of sound at T = 288.15 K Figure 2. Refractive indexes of the ternary mixture Tween 20 (1) Water (2)+ Na 2 S 2 O 3 (3) for 1.93% Na 2 S 2 O 3 : ; Tween 20 (1) Water(2)+ Na 2 SO 4 (3) for 1.56% Na 2 SO 4 , T = 288.15 K. Figure 4. Effect of mixture composition upon speed of sond. Tween 20(1)+Water (2) + Na 2 S 2 O 3 (3) (for 1.93% Na 2 S 2 O 3 ):  288.15 K, 298.15 K,  308.15 K, 318.45 K and Tween 20 (1) + Water (2) + Na 2 SO 4 (3) (for 1.56% Na 2 SO 4 ): 288.15,  298.15, 5,308.15,  318.15 Density (  ) of liquid pure components (Tween 20 and Water) and the ternary mixtures of different compounds (Tween 20 + Water + Na2SO4 or Na2S2O3) were measured with an Anton Paar DSA 5000 vibrating tube densimeter and sound analyzer. Refractive index was determined using an Abbemat Automatic Refractometer and before measurements, the equipment was calibrated using distilled water using the instrument instructions. Density behavior for both ternary systems (Tween 20 + Water + Na 2 S 2 O 3 and Tween 20 + Water + Na 2 SO 4 ) are similar obtaining a increase in the values of the physical properties (refractive indexes, density and speed of sound) when the mixtures enriched in Tween 20 (see Figures 1, 2 and 3). In Figure 4, there are the speed of for both ternary systems for the temperate 288.15 K, 298.15 K, 308.15 K and 318.15 K. The value of the speed of sound increase with the increase of Tween20 concentration, is possible to observe a maximum value and the graphs intersect at a point shown a temperature resistance system that could be related with an aggregation process. The presence of salts tends to decrease the Tween20 concentration to reach this temperature resistance structure. In figure 5, there are the binodal curves and the tie lines of the both systems (Tween 20 + Water + Na 2 SO 4 and Tween 20 + Water + Na 2 S 2 O 3 ) Na 2 SO 4 Figure 2. Refractive indexes of the ternary mixture Tween 20 (1) Water (2)+ Na 2 S 2 O 3 (3) for 4.86% Na 2 S 2 O 3 : ; Tween 20 (1) Water(2)+ Na 2 SO 4 (3) for 4.98% Na 2 SO 4 , T = 288.15 K. Figure 5. Binodal curves and tie lines of the systems: Tween 20(1)+Water (2) + Na2SO4(3) and Tween 20 (1) + Water (2) + Na2S2O3 (3) Authors acknowledge to E.Q.E.A. group at the University of Vigo for the facilities they have to carry out this research Na 2 SO 4 Na 2 S 2 O 3 Na 2 SO 4 Na 2 S 2 O 3 Abstract & IntroductionExperimental set-up Results & Discussion