Polymeric Sol–Gel Transition with the Diverging Correlation Length Verified by Small-Angle X-ray Scattering
K. Aoki, Ayae Sugawara‐Narutaki, Rintaro Takahashi
Abstract
High Resolution Image Download MS PowerPoint Slide Sol–gel transitions of polymers are pivotal phenomena in material science, yet the critical phenomenon of structure during gelation has remained unclear. Here, we investigated the sol–gel transition of a fluorous polymer, poly(vinylidene fluoride- co -hexafluoropropylene), in a blend of two ionic liquids. This system features a quite high amount of cross-linker and binding sites with ion–dipole interactions between the cation and C–F dipoles, thereby facilitating easy exchange of the cross-links. Changing the mixing ratio of the two ionic liquids enabled tuning the ion–dipole interactions and inducing sol–gel transition. Notably, the correlation length and molar mass, obtained by small-angle X-ray scattering, diverged at the gelation point. Moreover, the derived critical exponents (ν = 0.85 ± 0.05) aligns remarkably well with the prediction from percolation theory (ν = 0.88). To our knowledge, this is the first report on the evident divergence during polymeric gelation by small-angle scattering and the verification of the critical exponents of the percolation theory.