Water in Solutions of Chaotropic and Kosmotropic Salts: A DifferentialScanning Calorimetry Investigation

The use of aqueous phase separations via aqueous biphasic systems (ABS) has been widely explored in the recent decades. For wider and more “intelligent” applications, it is important to look below the surface and study these systems thoroughly at a fundamental level. Two important questions still unsolved are how do polymers and ions of different types organize water (if they in fact they do so) and how does it affect the separation of phases? In the present work, differential scanning calorimetry (DSC) was used to relate ABS phase diagrams and the behavior of water in aqueous solutions containing kosmotropic salts (K3PO4 or (NH4)2SO4), a chaotropic ionic liquid ([C4mim]Cl), or a polymer (PEG-2000), all of which are reported components of ABS, and their mixtures. Additional DSC transitions were observed for the two classes of salts which could be assigned based on the fundamental differences between their interactions with water, suggesting that it is the differences in the abilities of kosmotropic and ch...