Tuning triboelectric and energy harvesting properties of dielectric elastomers via dynamic ionic crosslinks

The bromination of poly(isobutylene-co-isoprene) rubber introduces a small amount of bromide groups (1-2 mol%) to the elastomer backbone and creates new opportunities for functionalisation, as compared to other saturated and diene elastomers. In this work, three types of nucleophile reagents: namely pyridine, triphenylphosphine and imidazoles bearing four types of side groups of methyl, ethyl, hydroxyl or vinyl group were introduced to brominated poly(isobutylene-co-isoprene) rubber (BIIR) through nucleophile substitution with the bromine via solid-state rubber compounding and curing processes. The resulted ionic aggregates act as physical crosslinks and their size and density directly affected the mechanical reinforcement, self-healing and dynamic mechanical properties of the elastomers. The smaller and polar imidazolyl/bromine pairs led to the highest reinforcement beyond even the sulfur-cured BIIR counterparts. The 1-ethyl imidazole (EIm) modified BIIR showed the highest tensile strength of 17.01 ± 1.89 MPa and elongation at break of 1402 ± 69% with self-healing efficiency of 63.7%, after being treated at 140 °C for 30 min. In addition, the inclusion of the ionic clusters enhanced the relative permittivity of the elastomer, thereby enhancing the energy conversion efficiencies. The nucleophile substitution reaction via conventional solid-state rubber compounding processes provides a facile crosslinking and reinforcement strategy for halogen-containing polymers. In addition, the dynamic ionic crosslinking networks spontaneously benefit electromechanical and self-healing properties of the dielectric elastomers.