Gelation process of polyacrylonitrile solutions as studied using small-angle neutron scattering techniques

Nakano, Shota*; Konno, Soken*; Tomita, Naoto*; Matsuba, Go*; Tominaga, Taiki*; Takata, Shinichi  

We studied the structural formation process of polyacrylonitrile (PAN) gelation in a wide-spatial scale with the small and wide angle neutron scattering in MLF, J-PARC. In micron-scale structure, light transmittance and gelation time were evaluated. The presence of water in the mixed solvent accelerated the phase separation and gelation. In the opaque-gel case, we observed the nanometer-scaled correlation of crystalline cross-linking points and smooth boundary of two micron-scaled phases due to liquid-liquid phase separation. The correlation length is independent of the annealing time, then the cross-linking point exists locally and micro-gelation occurs during phase separation. By contrast, in the transparent-gel case, the correlation length was found to increase throughout the gelation process, and the entanglements of the polymer chains play a role similar to that of cross-linking points.