Polymer solvation in choline chloride deep eutectic solvents modulated by the hydrogen bond donor

Abstract

Choline chloride (ChCl) Deep Eutectic Solvents (DESs) are a relatively new class of ionic fluid physicochemically similar to ionic liquids. Their properties, combined with their hydrogen bond - rich bulk nanostructures make them attractive alternatives as molecular solvents for a range of applications. Nevertheless, the solvation structure of molecular and polymer solvents in choline chloride DES remains largely uncharacterised due to the complexity of the DES nanostructure itself. We present a systematic quantum chemical investigation of the solvation structure of poly(ethylene glycol) (PEO) in DES formed by ChCl and urea, ethylene glycol and glycerol hydrogen bond donors. Trends in the solvation structure of PEO correlate with the density of the DES hydrogen bond network, and the extent to which this network can be perturbed by the polymer solute. We show that both of these factors are modulated by the type of hydrogen bond donor itself. Notably, PEO disrupts the urea – choline hydrogen bond network. This disruption leads to a more highly structured solvation environment for the polymer, which is forced into a relatively constrained, coiled morphology. By contrast, the disruption to the hydrogen bond networks in the ethylene glycol and glycerol DES are less significant, leading to a less constrained environment.