Supramolecular Ion Conducting Membranes

点击翻译按钮获取中文摘要

We will develop ion-selective membranes by directed self-assembly where the ion channels are formed by supramolecular complexes. Previously, we have shown that wedge-shaped amphiphilic π-stacked molecules with focal hydrophilic sulfonic acid head groups can self-assemble into supramolecular columns, in which the sulfonic groups are stacked to form well defined ion channels. The width and thus the flux through these ion channels can be controlled by the molecular structure of the assembling molecules. The columnar channels will be covalently stabilized by cross-linking and interconnection to a polymer matrix after orientation normal to the surface of the resulting membranes. The membranes will be prepared by photo- or thermo-polymerization of oriented films. The chemical structure of the wedge-shaped molecules will be optimized by mapping the phase diagrams of the material via temperature-dependent X-ray scattering. Homeotropic orientation of the columns will be accomplished by varying the surface energy and topography of the substrate, and by applying electric and magnetic fields. Ion transport, local and macroscopic alignment of channels, and dynamics of the polymer matrix all represent key features of these materials. Multi-modal NMR measurements of ion diffusion, channel alignment, and channel defect structures will provide invaluable information for understanding and designing these novel materials. 2H NMR spectroscopy on absorbed ions and D2O, and on specific 2H labels attached to the supramolecular structures will report on material orientational distributions and will be complemented by transmission and grazing incidence X-ray scattering. Multi-axis NMR diffusometry and electrophoretic mobility measurements will give complementary information on the influence of membrane properties on ion transport. Ion conductivity experiments will be performed by impedance spectroscopy and by means of membrane potential measurements in a liquid cell. Selective structural variation including introduction of photochromic groups will be studied regarding the structure / conductivity relationships, and to obtain membranes with photocontrollable ion conductivity.