Amphiphilic cone-shaped cationic calix[4]arene composite anion exchange membranes with continuous ionic channels

A novel amphiphilic cone-shaped inducer, tetra-quaternized tetraoctyloxycalix[4]arene (TQCX), is proposed to create continuous ionic channels in an anion exchange membrane (AEM). Via molecular dynamics simulation, it was found that four upper-rim cationic groups induce ionic aggregation via electrostatic interactions, while four lower-rim hydrophobic octyl side chains promote the clustering of hydrophobic domains via van der Waals interactions with the polymer backbone. The core cavity in TQCX introduces additional free volume to connect hydrophilic domains. At the optimal TQCX content of 3 wt%, the ionic clusters with a diameter of ∼12 nm are induced, and even linearly arranged to construct continuous ionic channels with a length up to ∼300 nm. Besides, TQCX also aggregates to form the ion-rich nanoparticles with the size of ∼500 nm, which also assist in the construction of interconnected hydroxide-conducting pathways. Consequently, hydroxide conductivity of the composite membrane yields a 70% improvement at 3 wt% TQCX over that of the pristine membrane, achieving the top level among the reported main-chain-type AEMs based on the polysulfone backbone.