The formation and physicochemical properties of PEGylated deep eutectic solvents

Deep eutectic solvents ( DESs) have attracted considerable attention due to their unique properties. In recent years, novel deep eutectic solvents based on polyethylene glycol ( PEG) have been proposed, which are called PEGylated DESs. Owing to their excellent properties, PEGylated DESs have been applied in many fields, such as extraction, biomass dissolution and material preparation. For better application of PEGylated DESs in various fields, the solid understanding of their fundamental properties is indispensable. In this work, nine PEGylated DESs based on carboxylic acids, amides and ammonium salts were prepared and characterized by FTIR, 1H NMR and DSC analysis. The physicochemical properties including pH values, polarity, density, viscosity, conductivity, and thermal stability were investigated. Walden plot analysis was also conducted in order to evaluate the ionicity of the PEGylated DESs. The nature of the components plays a vital role in the properties of the PEG based DESs. There is a negative correlation between the pH values and polarity of the PEGylated DESs, which can be applied to infer the polarity via pH measurement. The density and viscosity gradually decrease with increasing temperature due to thermal expansion. Except for the ammonium salt based DESs, the PEGylated DESs exhibit a `` poor ionic'' nature and have a negligible conductivity owing to the lack of ionic species. According to the above research, PEGylated DESs with specific properties could be elaborately designed via choosing appropriate components, thus facilitating their application.