Ionic Liquid Cation Size-Dependent Electromechanical Response of Ionic Liquid/Poly(vinylidene fluoride)-Based Soft Actuators

This work reports on the development of ionic liquid (IL)/poly­(vinylidene fluoride) (PVDF) actuator composites. ILs sharing the same anion (bis­(trifluoromethylsulfonyl)­imide, [TFSI]⁻), and different cations belonging to the families of pyridinium, imidazolium, and ammonium ions, comprising an alkyl side chains with variable length, were used. The physical–chemical properties, thermal behavior, mechanical, electrical, and bending responses of the PVDF/IL composites were evaluated. The incorporation of ILs into the PVDF matrix leads to an increase of the electroactive β phase content. Moreover, the β phase content increases with the increase of the IL alkyl chain length. The degree of crystallinity depends on the IL chain length as well as on the mechanical properties, revealing the plasticizing behavior exerted by the IL. The electrical conductivity decreased with the increase of the cation alkyl chain size. The highest bending response was observed for the [Pmim]­[TFSI]/PVDF and [Pmpip]­[TFSI] composites (where Pmim and Pmpip represent propylimidazolium and propylmethylpiperidinium), being 5.7 and 6.0 mm, respectively, at 5 V and 100 mHz.