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‐d6) and D2O 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 Å−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 Å below ≈70°C, suggesting that the crystallite surface is smooth and the average distance between the neighboring crystallites is ≈150Å. 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. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 157–160, 2005