Heterogeneous Decoration of Ionic Mesopores by Ionic and Poly(Ionic) Liquids

Understanding the molecular structure of mesoporous solid ionic systems is essential for optimizing their macroscopic properties, such as enhanced ionic transport for energy applications and improved mechanical flexibility. These systems can be synthesized efficiently using "one-pot" conditions, where mesopores form via the microphase separation of a templating ionic liquid. Furthermore, incorporating poly(ionic liquid)s can improve structural connectivity and tailor the mechanical strength of the material. We report on the structural analysis of ionic liquid and poly(ionic liquid) embedded in ionosilica matrices, employing a combination of small-angle scattering of neutrons and X-rays, isotopic substitution, and physicochemical solvent-based extraction methods. Data analysis is based on an original, quantitative comparison of scattering curves obtained under different contrast conditions. It is shown that these mesoporous systems have an unexpected molecular structure, with the ionic liquid counterions penetrating the ionosilica matrix surrounding the mesopores, their presence being confirmed by NMR spectroscopy. The poly(ionic liquid) forms patches decorating the pore walls, with tunable conformation sensitive to solvent conditions. This behavior is anticipated to be generic in self-assembled ionosilica systems, due to the separation of the ionic liquid from the matrix, while the polymer chains have affinities for both matrix and ionic liquid.