Small-angle neutron scattering studies on network structure of transparent and opaque PVA gels

Small-angle neutron scattering measurements have been carried out on transparent and opaque poly vinyl alcohol (PVA) gels formed in a mixture of dimethyl sulfoxide and water with a volume ratio 60/40 to investigate the network structure of the gels, It was found that the correlation length of the network. which corresponds to an average distance between the nearest neighboring cross-linking points, is independent of the PVA concentration for the opaque gel, while it depends on the concentration for the transparent gel. This result is discussed by taking into account the previous findings that spinodal decomposition type liquid-liquid phase separation takes place before the gelation in the opaque gel, but does not in the transparent gel. The size of the cross-linking points, which are crystallites in the present gel, is also discussed on the basis of the distance distribution analysis of the scattering data. (C) 2002 Elsevier Science B.V. All rights reserved.