Ion Selective Transport of Alkali Ions through a Polyelectrolyte Membrane

The ionic conductivity of a polyelectrolyte membrane consisting of 30 bilayers of poly(allylamine hydrochloride) and p‐sulfonato‐calix[8]arene, (PAH/calix8)30, is investigated for two alkali ions, i.e., Li+ and Rb+. Two different transport pathways, a fast and a slow one, are identified for Li+ transport. By contrast, only the fast transport pathway is observed for Rb+ transport. This fast transport pathway is assigned to regular hopping through bulk material, whereas the slow transport pathway originates from retarding interaction with the calixarene rings, only operative for Li+ but not for Rb+. This observation constitutes a clear manifestation of ionic selectivity for transport in polyelectrolyte membranes. Selectivities in the transport pathways for alkali ions through ultrathin polyelectrolyte membranes are demonstrated.