Small-angle neutron scattering study of poly(vinyl alcohol) gels during melting process

Small-angle neutron scattering (SANS) measurements were performed on poly(vinyl alcohol) (PVA) gels in a mixture of deuterated dimethyl sulfoxide (DMSO-d 6 ) and D 2 O with volume ratio of 60/40 to see the structure changes of the crosslinking points, which are crystallites, and of the gel network during the melting process. The observed SANS intensities were fitted to the Ornstein-Zernike (OZ) formula and a power law in scattering vector Q ranges from 0.01 to 0.035 and 0.05 to 0.1 A -1 , respectively, to evaluate the correlation length ξ and the power law exponent n. It was found that the exponent n is 4 and the correlation length ξ is ∼ 150 A below 70°C, suggesting that the crystallite surface is smooth and the average distance between the neighboring crystallites is 150A. On the other hand, they begin to decrease >70°C. The decrease of n suggests that the surface of the crystallites becomes rougher with increasing temperature. As for the correlation length ξ, analyses in terms of distance distribution function suggested that the decrease of ξ is apparent, and the intercrystallite distance increases with temperature >70°C because the crystallites decrease in number because of melt.