Structural Organization of Poly(vinyl alcohol) Hydrogels Obtained by Freezing/Thawing and γ-Irradiation Processes: A Small-Angle Neutron Scattering (SANS) Study

The structural organization of poly(vinil alcohol) (PVA) hydrogels obtained by repeatedly freeze/thaw and γ-irradiation processes of 15% w/w PVA solution in D2O has been revealed by small-angle neutron scattering (SANS) technique. The opaque sample is due two separated phases which composed by polymer-rich and polymerpoor regions occurred from freezing/thawing samples, while transparent sample formed from irradiated PVA hydrogels sample. It has been pointed out from SANS experimental data that the cross-linking in the gels formed by freezing/thawing process are crystallites as the scattering intensity I(Q) decreases with the momentum transfer Q according to the -4th power law (Porod's law) in the high Q-range region. From SANS data analysis, the radius of the crystallite size is about 28 - 33Å and its distributed inhomogeneously with the average distance of 150 - 175Å in the polymer-rich phase that consisted by crystalline PVA aggregates and swollen amorphous PVA. In opposite, the irradiated PVA hydrogels with the irradiation dose of 40 kGy did not show a -4th power law scattering due to in absence of crystalline and amorphous PVA phases in the polymer-rich region.