Polyethylene glycol (PEG) is a well-known water retention agent in biomedical products, the hydration efficiency of which is affected by its molecular weight. Using a broadband dielectric spectroscopy (100 MHz–18 THz), the hydration state of PEG aqueous solutions with various molecular weights was quantitatively evaluated. As the molecular weight increases, the restriction strength of hydration water increases in potency, while the number of hydration water molecules decreases. Owing to the opposite changes in hydration number and restriction strength, the measured collective hydrogen bond (HB) strength shows negligible molecular weight dependence. PEG with larger Mw produces a more heterogenous HB network. The internal folding and twining caused by the growth of the PEG chain obstruct the proper exposure of hydrophilic part of the monomer producing less hydration waters. The evaluation result supports an application of PEGs with low molecular weight in contact lens package solutions.
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