Novel electroactive polymer actuators using all-polyelectrolyte poly(ionic liquid) ionogels

Poly(ionic liquid)-based ionogels are excellent all-poly(electrolyte) candidates for electroactive actuation applications, but investigation of their actuation behavior and ionogel properties has largely been limited to styrenic block copolymers. In this work, ionogels were prepared from a novel poly(ionic liquid) (PIL) block copolymer, poly[(2-dimethyl amino)ethyl methacrylate)]-block-poly[4-vinylbenzyl-3-butyl imidazolium bis(trifluoromethylsulfonyl)imide] (PDMAEMA-b-PVBBImTf₂N) combined with an ionic liquid, 1-butyl-3-methyl imidazolium tetrafluoroborate (C₄C₁ImBF₄), at weight percentages between 0 to 40 wt%. Under a low applied voltage (4 V DC) microscale actuation was achieved for films prepared from the neat PDMAEMA-b-PVBBImTf₂N block copolymer, as well as its corresponding 10 wt% ionogel; this result critically expands the PIL block copolymer chemistries available for electroactive actuator applications. Thermal, ionic conductivity, morphology, and mechanical modulus properties of the PDMAEMA-b-PVBBImTf₂N ionogels were also assessed to evaluate their potential for electrochemical applications. Addition of the ionic liquid to form an ionogel significantly increased the thermal stability of the PDMAEMA polymer block and successfully plasticized the PDMAEMA-b-PVBBImTf₂N block copolymer ionogel, as evidenced by decreases in the glass transition temperature and significant enhancement of the ionic conductivity from ∼10⁻⁷ S/cm in the neat polymers to ∼10⁻⁴ S/cm in the 40 wt% ionogels. AFM force curve analyses using a Derjaguin-Muller-Toporov (DMT) model showed a reduction of Young’s modulus for the block copolymer matrix as a function of increasing ionic liquid content, and the PDMAEMA-rich phase exhibits a higher modulus, which serves to mechanically reinforce the PIL matrix. In combination the material properties and electrical responsiveness of these novel all-polyelectrolyte PDMAEMA-b-PVBBImTf₂N block copolymer ionogels show excellent potential for micro-scale electroactive actuation and other electrochemical applications.