Hydration behavior of poly(ethylene oxide)s in aqueous solution as studied by near-infrared spectroscopic techniques.

Near-infrared (NIR) absorption measurements over a wavenumber range from 4000 to 12000 cm(-1) were used to investigate hydration behavior of poly(ethylene oxide)s bearing molar masses of 3 × 10(3) (PEO3) and 20 × 10(3) (PEO20) in aqueous solution at a dilute regime. NIR absorption spectra for solutions were perfectly decomposed into three components: bulk water, PEOs, and hydrated water to PEOs. While amounts of each component were proportional to the concentrations of PEOs (cEO), the wavenumber dependence of each spectrum was independent of cEO and also the molar masses of PEOs. A newly determined NIR absorption spectrum of hydrated water molecules to PEOs found in a wavenumber range from 5500 to 7500 cm(-1) was well described with the summation of two Gaussian-type vibration modes possessing the same magnitude, which were observed at different wavenumbers of 6480 and 6910 cm(-1), respectively. Each mode was assigned to O-H stretching first overtone of water molecules hydrated directly to ether oxygen atoms (6480 cm(-1)) and water oxygen atoms (6910 cm(-1)) belonging to the secondary hydration layer.