Solute–solvent interactions within aqueous poly(ethylene glycol): solvatochromic probes for empirical determination and preferential solvation

Due to their vast industrial importance, poly(ethylene glycols) [PEGs] have become substances of major investigations. The hypothesis that aqueous PEG rather than pure PEG may provide substantially improved physicochemical properties for many industrial applications is addressed. Solvatochromic electronic absorbance probes are utilized to gather important information about these systems. Response from a water-soluble betaine dye suggests a decrease in dipolarity/polarizability and/or hydrogen-bond donating (HBD) acidity as the PEG is added to water. This is further confirmed by the response of N,N-diethyl-4-nitroaniline, which shows a decrease in dipolarity/polarizability and, in concert with the response from the betaine dye, a decrease in HBD acidity as the amount of PEG is increased. Response from 4-nitroaniline combined with dipolarity/polarizability is used to show that hydrogen-bond accepting (HBA) basicity increases with the addition of PEG to water. The extent of change in these important physicochemical properties depends on the PEG molecular mass. A simple mole-fraction weighted solvation model suggests significant preferential solvation of the betaine dye by PEG molecules in aqueous PEG solutions.