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 determ ined by means of neutron scattering. G(Hp)(r) was obtained from the fi rst-order difference taken from the scattering functions of deuterated and hydrogenated poly(ethylene oxide) solutions in D2O. The intramole cular partial structure functions were calculated using a rotational i someric state model. The distribution of water around the polymer prot ons was obtained by subtracting the intramolecular partials from G(Hp) (r) NO evidence of structured water at the polymer interface is observ ed. Our results show that the tetrahedral cavities in water are too sm all to accommodate the polymer, and it cannot therefore be assumed to be hydrated by an unperturbed tetrahedral water lattice. The cavity su rfaces of various rotameric forms of poly(ethylene oxide) oligomers ha ve been calculated. The results show that, on average, six water molec ules 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 hyd ration number consistent with our experimental results.