Water interaction with oligo-(ethoxy) ethylene glycols

The amount of water sorbed by oligo-(ethoxy)ethylene glycols of the homologous series HO(CH2CH2O)nH, En, with n = 1…8 was determined by the isopiestic method at constant relative humidities RH from 11% up to 97% at 25°C. We found that the sorption isotherms extracted can be described using a regular solution theory used for poly-(ethoxy)ethylene glycols. For the amount of water sorbed at constant RH we found an approximately linear dependence on the number of ether oxygens per glycol, indicating a constant number of water molecules per group, which was estimated for all RH. Furthermore, spin-lattice relaxation times of deuterium oxide (2H2O) in a large concentration range of ethylene glycols in heavy water were measured at the same temperature and for all glycols the free energy of water binding was deduced from these measurements using a two-state model.