STRUCTURE OF POLY(VINYL ALCOHOL) GELS STUDIED BY WIDE-ANGLE AND SMALL-ANGLE NEUTRON-SCATTERING

The structure of poly(vinyl alcohol) (PVA) gels formed in a mixture of deuterated dimethyl sulfoxide (DMSO-d6) and heavy water at 23-degrees-C has been investigated by wide- and small-angle neutron scattering techniques. It was directly confirmed from the wide-angle neutron scattering measurements that cross-linking points or junction points in the gels are crystallites. In the small-angle scattering measurements, it was found that the scattering intensity I(Q) decreases with Q according to the -4th power law (Porod's law) in the Q range above 0.05 angstrom-1 where Q = 4pi sin theta/lambda (2theta and lambda are scattering angle and wavelength of neutron, respectively), suggesting that the surface of the crystallites has a clear boundary. On the other hand, the Q dependence of the scattering intensity I(Q) can be described by I(0)/[1 + xi2Q2] in the Q range below 0.035 angstrom-1, where xi is a correlation length. The correlation length xi was assigned to the average distance between the neighboring crystallites. Distance distribution function P(r) which is defined by inverse Fourier transformation of scattering intensity I(Q) was also calculated in order to see another aspect of the scattering intensity. Two peaks or shoulders at about 70 and 200 angstrom were recognized in the calculated P(r). The former and the latter have been attributed to the intra- and intercrystallite correlations, respectively. By separating the two correlations, the distribution of the crystallites is discussed.