Water hydration of polyethylene glycol dimethyl ether.

This article focuses on the GHz and THz dielectric relaxation dynamics of water in aqueous solutions of polyethylene glycol dimethyl ether (PGDE, molecular weight 2000 g/mol). Using combined GHz–THz dielectric spectroscopy and three Debye relaxation models, the study identifies three distinct water components: fast (under-coordinated) water, bulk-like water (including bulk water and hydrophobic hydration water), and slow hydrating water (water donating hydrogen bonds to hydrophilic ether groups). The research quantifies the relaxation timescales, proportions, and molecular numbers of these water types at varying PGDE concentrations (5%–60%), revealing that slow hydrating and fast water fractions increase with concentration while bulk-like water decreases. Experimental Kirkwood factors, reflecting dipole correlations, were calculated for each water component, showing an increase for bulk-like water and a relatively constant value for slow hydrating water, consistent with their differing hydrogen bonding environments around PGDE molecules.