Polymer electrolytes based on a homogeneous poly(ethylene glycol) network and their application to polymer actuators

Abstract

Polymer electrolytes consisting of a homogeneous poly(ethylene glycol) (PEG) network and Li[NTf2] ([NTf2]: bis(trifluoromethanesulfonyl)amide) were prepared by an addition reaction between two tetra-arm PEGs (tetra-PEG; Mn = 10,000) with a maleimide group and an amino group at the polymer ends. Their properties were compared with those containing [C2mim][NTf2] ([C2mim]: 1-ethyl-3-methylimidazolium). Michael addition reaction between the maleimide and amino groups yielded polymer electrolyte membranes with homogeneous network structures. The glass transition temperature (Tg) of the polymer electrolytes containing Li[NTf2] was observed to be lower than those of conventional polymer electrolytes using PEG. The low Tg values contributed to relatively high ionic conductivity (6.3 × 10−5 S cm−1 at 30 °C with [Li]/[O] = 0.10) compared to that of conventional polymer electrolytes. Moreover, superior mechanical properties including an elastic modulus of 171 kPa and fracture energy of 1890 kJ m−3 were achieved due to the homogeneous network structure. Furthermore, the electroactive actuation behaviors of polymer actuators using polymer electrolytes containing either Li[NTf2] or [C2mim][NTf2] were explored. The Li[NTf2]-based polymer actuator was observed to exhibit larger displacement with slower response compared to the [C2mim][NTf2]-based actuator. The bending directions were opposite in these two actuators. These behaviors were well described by a model that considers the ionic volume and ionic transference number of the polymer electrolytes.