Phase inversion behavior of poly(ethylene glycol) + NaOH + water aqueous two-phase systems (ATPSs): Effect of polymer molar mass

In the last decades, the phase inversion behavior of aqueous two-phase systems (ATPSs) has been commonly reported for some systems. For instance, some ATPSs formed by poly(ethylene glycol) (PEG) and electrolyte, extensively employed in processes of separation and purification of strategic solutes, exhibit that behavior [1]. This unique phenomenon was proved to be dependent on the temperature and composition of the system, however the effect of the molar mass of the polymer was not discussed. Here, investigation was made of the effect of the PEG molar mass on the phase inversion behavior of ATPSs formed by PEG, sodium hydroxide, and water. For the experiments, PEGs of molar masses of 1500, 4000, 10000, and 20000 g mol-1 were used to prepare the ATPSs in three different compositions. Each system was placed in a bath with controlled temperature (25-80 °C) and allowed to separate phase. A dye that concentrated in the PEG-enriched phase was used as probe to identify the temperature in which the phase inversion occurred. As a general result, inside the biphasic region, higher temperatures and smaller global compositions favored the formation of ATPSs in which the bottom phase was observed to be the PEG-enriched phase. This result was contrary to the feature described for the most of ATPSs, in which the PEG-enriched phase was the top phase [2]. The phase inversion behavior was caused by density changes in the phases, and it occurred in lower temperatures when the PEG molar mass increased (Fig. 1).