(Invited) Formation Process and Structure of Poly (acrylonitrile) Gels

Abstract

We carried out small angle neutron scattering measurements to clarify the gelation processes of 10 wt% polyacrylonitrile solutions in various water contents. The water in the mixed solvent was accelerated with the phase separation and gelation because of poor solubility of poly(acrylo-nitrile) (PAN) in water. The solute is amorphous PAN with weight-average molecular weight of Mw = 250,000 and a molecular weight distribution Mw / Mn = 1.8. Mixed solvent is DMF / H2O (0 ~ 9 wt%). amorphous PAN was dissolved in mixed solvent at 90 ºC (PAN : mixed solvent = 10 : 90) after quenching at room temperature. In order to observe the structure and formation process of PAN gels, we used various kinds of scattering methods, e.g. light scattering, small angle X-ray scattering (SAXS). These measurements conducted at room temperature. Time-resolved SAXS was performed using an apparatus installed at beamline BL10C, Photon Factory, KEK (Tsukuba, Japan). The wavelength of X-ray beam was 1.488 Å. The camera length was 2.0 m for SAXS measurements. The inhomogeneities of polymer chains grow just after quenching then the correlation length increases with time at first. In the opaque gel case, we found the growth of crosslinking points with smooth surfaces. Around the gel point, the crosslinking points emerge and then, the correlation length decreases with time since increasing the crosslinking points. On the other hand, in the transparent gel, we did not observe scattering from surface of crosslinking points but only the correlation length. The correlation length increases during gelation process, then the entanglements of polymer chains play a role of crosslinking points.