Mechanically Adaptive Mixed Ionic-Electronic Conductors Based on a Polar Polythiophene Reinforced with Cellulose Nanofibrils

Conjugated polymers with oligoether side chains are promisingmixedionic-electronic conductors, but they tend to feature a low glasstransition temperature and hence a low elastic modulus, which preventstheir use if mechanical robust materials are required. Carboxymethylatedcellulose nanofibrils (CNF) are found to be a suitable reinforcingagent for a soft polythiophene with tetraethylene glycol side chains.Dry nanocomposites feature a Young's modulus of more than 400MPa, which reversibly decreases to 10 MPa or less upon passive swellingthrough water uptake. The presence of CNF results in a slight decreasein electronic mobility but enhances the ionic mobility and volumetriccapacitance, with the latter increasing from 164 to 197 F cm(-3) upon the addition of 20 vol % CNF. Overall, organic electrochemicaltransistors (OECTs) feature a higher switching speed and a transconductancethat is independent of the CNF content up to at least 20 vol % CNF.Hence, CNF-reinforced conjugated polymers with oligoether side chainsfacilitate the design of mechanically adaptive mixed ionic-electronicconductors for wearable electronics and bioelectronics.