Tuning the Mechanoelectrical Transduction Performance of Multifunctional Polymer Electrolyte Membranes via Variation of Precursor Molecular Weight

The phenomenon of flexoelectricity generation in response to applied mechanical deformation via bending of a multifunctional polymer electrolyte membrane (PEM) conetwork was investigated systematically by varying the molecular weight of the ion-solvating polymer precursor. The functional network consisting of multiarm poly(ethylene imine) (PEI) and poly(ethylene glycol) diglycidyl ether (PEGDGE) was copolymerized by means of ring-opening polymerization of epoxy with amine in the presence of the succinonitrile (SCN) plasticizer and lithium bis(trifluoromethane sulfonyl) imide (LiTFSI) salt. With increasing molecular weight of the linear PEGDGE precursor, not only did the conetwork become more flexible, but segmental chain motion was also expedited, leading to lower glass transition temperature (Tg) and higher ionic conduction. Concurrently, the mechanoelectric response of symmetric carbon/PEM/carbon laminates, i.e., flexoelectric coefficient (μ), increases with increasing PEGDGE precursor molecular weight. During the intermittent bending of the highest molecular weight, i.e., PEI-co-PEGDGE1000/LiTFSI in a 95/5 weight ratio, the flexoelectric coefficient was found to be about 519.2 μC/m, which is the highest among all materials hitherto reported. Of particular interest is that the developed PEM, i.e., PEI-co-PEGDGE1000/LiTFSI 95/5, exhibits excellent flexoelectric performance with a high mechanoelectric energy conversion efficiency of 13.7%, which opens new opportunities for energy harvesting and sensing devices.