Mimicking nature: Biomimetic ionic channels

Abstract Membranes with a high but remarkably humidity-independent proton conductivity were prepared. Side-chain liquid crystalline polyethers (SCLCPs), based on poly(epichlorohydrin) (PECH) and poly(epichlorohydrin-co-ethylene oxide) (P(ECH-co-EO)), dendronized with potassium 3,4,5-tris[4-(n-dodecan-1-yloxy)benzyloxy]benzoate were specially designed for this purpose. When cast as membranes, these tailored polymers self-assembled into columns, driven by exo-recognition. They thus mimic the highly specific supramolecular organization observed in nature and present the first biomimetic material for proton transport out of which stable, oriented and self-sustained membranes could be prepared. As revealed by combined X-ray diffraction, Atomic Force Microscopy and Transmission Electron Microscopy, polymeric column formation was obtained in the cast membranes following a thermally induced homeotropical orientation. Two unique and highly desired properties were found in the resulting membranes. While conventional proton conducting membranes exploit an “acidic group-based” transport mechanism, the current columns pillaring across the membranes formed ionic paths, giving rise to a remarkable size-dependent antiport transport mechanism. It resulted in conductivity values in the range of 10 −2 –10 −3  S/cm, comparable to current state-of-the-art Nafion membranes, but, most importantly, with a complete independency from relative humidity. Reported membranes thus open excellent opportunities for further fine-tuning of their properties, wider exploitation of the exceptional transport mechanism, and final applications in fuel cells and related fields.