SANS studies on frozen inhomogeneities and local structure in polymer gels

The structure factor S(q) for a series of poly(N-isopropylacrylamide-co-acrylic acid) (NIPA/AAc)copolymer gels having different cross-link concentrations has been investigated by small-angle neutron scattering for a wide range of scattering vector q. The range of q was covered to be 0.07 ≤ q ≤ 6 nm-1 by measuring S(q) with three different sample-to-detector distances, i.e., 1, 5, and 15.3 m. This allowed a quantitative analysis of the interaction parameters both at gel preparation and at observation. A positive deviation of the scattered intensity at low q-region was observed and was explained by additional built-in inhomogeneities and by chain-entanglement effects introduced during the process of gel formation. A positive deviation was also found at the large-q limit, which was interpreted as an increase in the local chain rigidity by introduction of crosslinks. (author)