Do the liquid-free poly(ionic liquids) have good environmental reliability?

The poly(ionic liquids) (PILs) are often considered to own good stability and frequently adopted to design liquid-free ionic conductive materials, yet the environmental reliability that determines the stability of PILs has not been experimentally demonstrated. Here, three PIL ionoadhesives including homopolymer, copolymer and chemically crosslinked copolymer are fabricated and their environmental reliability has been studied through aging treatment under high temperature and high humidity. It is discovered that the bonding strength of PIL ionoadhesives drastically dropped by a sharp percentage (34.9–52.0 %) in the first 24 h and maintained stable in the following aging period. The investigation to the failure mechanism reveals the environmental reliability of PIL ionoadhesives is seriously destroyed by humidity due to the strong interactions between water molecules and ionic groups of PIL ionoadhesives, resulting in shielding of ionic groups that weakens the non-covalent interactions among PIL chains and the interfacial interactions between PIL ionoadhesives and substrates. This work reveals the environmental reliability of PILs and figures out the failure mechanism, which may provide a useful insight for further design of PIL materials.