Grafting high content of imidazolium polymer brushes on graphene oxide for nanocomposite membranes with enhanced anion transport

Abstract

Polymer functionalized nanoparticles have attracted burgeoning interests in designing and fabricating novel nanocomposite membranes for fast transport of ions or small molecules. Herein, imidazolium polymer coated graphene oxides (AImGOs), bearing different length of polymer brushes, are synthesized via ATRP technique, and thus a very high weight percentage of imidazolium polymer brushes on GO (up to 89.5%) is acquired, corresponding to a high IEC value up to 65.5 mmol g−1. The as-synthesized AImGOs are then dispersed into poly(vinyl alcohol) (PVA) to prepare nanocomposite membranes. The polymer brushes coated on AImGOs render better interfacial compatibility and filler dispersity. The large specific surface area and high aspect ratio of GO contributes to the enhancement of swelling resistance and mechanical stability of membranes. More importantly, the imidazolium polymer brushes on AImGOs endow the membrane with efficient OH– conduction ability due to the high loading of OH– hopping sites, the flexible chain, and the intrinsic large surface area of GO, demonstrating that efficient OH−-hopping pathways are constructed along the interface between PVA matrix and AImGO. By lengthening the polymer brushes, increasing AImGO content, and adopting appropriate types of imidazolium cations, a remarkable increment of OH– conductivity are observed. To be noted, long polymer brushes quaternized with ethyl chloroformate yield zwitterion type functionality, entitling the highest OH– conductivity of 31.6 mS cm−1 at 30 °C (100% RH).