Flexoelectric Ionic Liquid-Grafted Triblock Copolymers for Energy Harvesting under Flexural Deformation

The goal of the present article is to develop flexoelectric polyelectrolyte elastomers for energy harvesting based on a poly-(ethylene glycol)-block-poly-(propylene glycol)-block-poly-(ethylene glycol) dimethacrylate (PEG-b-PPG-b-PEG-DMA) triblock grafted with an ionic liquid (IL) such as allylmethylimidazolium bis-(trifluoromethane sulfonyl) imide (AMIMTFSI). The IL-grafted triblock copolymer network possesses a balance of reasonably good ionic conductivity and high ion polarization during cantilever bending. Of particular importance is the achievement of high flexoelectric coefficients in some flexoelectric polyelectrolyte elastomer (FPE) compositions reaching 1368 mu C/m at ambient temperature during mechanical deformation under intermittent square-wave bending mode. With the addition of a 10 wt % lithium bis-(trifluoromethane sulfonyl) imide (LiTFSI) salt, the flexoelectric coefficient further improved to 1737 mu C/m, which is the highest among all piezoelectric and flexoelectric materials hitherto reported, and thus it opens a new opportunity for clean energy harvesting from a vibrating natural environment.