Pressure, temperature and concentration effects on hydrogen bonding in poly(ethylene oxide) aqueous solution

Abstract

Poly(ethylene oxide) (PEO) is a biocompatible polymer and is widely used in biomedical application such as drug delivery devices. Such biomedical application is suitable due to high water solubility. However, the mixture of PEO and water is highly anomalous because of strong electrostatic attraction like hydrogen bonding interaction. The hydrogen bonding in PEO/water is an important fact to understand the miscibility (i.e., phase behavior) of PEO in aqueous solution and is influenced by temperature, concentration and pressure. The pressure in these factors has a strong effect on the production of the drug delivery material using supercritical fluid technology. In this work, the degree of hydrogen bonding for each molecule in aqueous PEO solution according to temperature, pressure and concentration has been investigated by perturbed-hard-sphere-chain-association (PHSC-AS) models. According to the increase of water concentration, the degree of hydrogen bonding for water-water self-association is gradually decreased, and that for cross-association between PEO and water are sharply increased. As well, according to the increase of temperature, all types of hydrogen bonding are decreased. The pressure-dependence of hydrogen bonding for each association site was not found up to 320 MPa. Such hydrogen bonding effect is considered in the modeling of phase behavior for aqueous PEO system with closed-loop type with the lower critical solution temperature (LCST) at low temperatures and the upper critical solution temperature (UCST) at high temperatures and hour-glass type up to 430 MPa. In general, the hour-glass type phase behavior is not found at atmospheric pressure and is found at the high-pressure range. The calculated results for liquid-liquid equilibrium (LLE) with closed-loop and hour-glass phase behavior showed a good agreement with experimental data.