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 X 10(3) (PEO3) and 20 X 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 (C-EO), 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) I, 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.