Remanent deformation and local stiffening induced by electric field in low glass transition epoxy-amine polymer network doped with ionic liquid

Abstract

Room temperature ionic liquids (RTILs) can behave like solids as the result of their ordering in the vicinity of substrates or confining in porous membranes. In this work, we have used this specific property to fabricate soft electroactuators in which deformation can be maintained after removal of the electric field. Epoxy-amine doped with 5%wt of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIM TFSI) was processed. The study of bending under a constant electric field of E=0.1 MV/m shows slow deformation kinetics as a function of time. Interestingly, when the electric field is removed, around 80% of the displacement is maintained for at least a day. The reversibility of this phenomenon was checked by successively applying positive and negative electric fields. It shows that complex successive electro-mechanical cycles can be performed without performance degradation (i.e. the sample reaches the same bending amplitude). Besides, energy dispersive X-ray spectroscopy was used to map the bis(trifluoromethylsulfonyl)imide counter anion before and after the application of the electric field and revealed the presence of a persistent anionic rich layer near the positive electrode after removing the electric field. This result was also supported by atomic force microscopy, which revealed an improvement in sample stiffness near the positive electrode. It explains the observed remanent deformation and opens up prospects for the processing of materials whose stiffness can be controlled by applying an electric field.