DISTRIBUTION OF WATER AROUND POLY(ETHYLENE OXIDE) - A NEUTRON-DIFFRACTION STUDY

The radial distribution function of the polymer protons (G(Hp)(r)) in a 1.88 monomolal aqueous poly(ethylene oxide) solution has been determined by means of neutron scattering. G(Hp)(r) was obtained from the first-order difference taken from the scattering functions of deuterated and hydrogenated poly(ethylene oxide) solutions in D2O. The intramolecular partial structure functions were calculated using a rotational isomeric state model. The distribution of water around the polymer protons was obtained by subtracting the intramolecular partials from G(Hp)(r) NO evidence of structured water at the polymer interface is observed. Our results show that the tetrahedral cavities in water are too small to accommodate the polymer, and it cannot therefore be assumed to be hydrated by an unperturbed tetrahedral water lattice. The cavity surfaces of various rotameric forms of poly(ethylene oxide) oligomers have been calculated. The results show that, on average, six water molecules can be packed on the surface of a monomer. Integration of G(intra)(exp)(r) over the typical dimensions of a water molecule yields a hydration number consistent with our experimental results.