Fast and large stretching bis(trifluoromethylsulfonyl)imide (TFSI)-doped polypyrrole actuators and their applications to small devices

Bis(trifluoromethylsulfonyl)imide (TFSI)-doped polypyrrole (PPy) films were prepared electrochemically from an aromatic ester solution of tetra-n-butylammonium bis(trifluoromethylsulfonyl)imide (TBATFSI) at -10 degrees C on various metal and carbon electrodes. TFSI-doped PPy actuators exhibited more than 20% electrochemical strains with fast response rate (< 13.8% s(-1)) when driven electrochemically in a propylene carbonate (PC)/water mixed solution of LiTFSI. The maximum electrochemical strain of TFSI-doped PPy actuators was 35.2%, which was equivalent to strains of mammalian skeletal muscles. The fast and large electrochemical strain was ascribed to smooth insertion and release of large dopant anions (TFSI), resulting from slight disentanglement and swell of TFSI-doped PPy films in PC/water solution of LiTFSI. Due to the moderate mechanical strength of TFSI-doped PPy films, TFSI-doped PPy should be supported by compliant metal electrodes such as metal micro-coils. Encapsulated artificial muscle fibres, comprising a TFSI-doped PPy Au coil composite actuator, a TFSI-doped PPy tube as the counter electrode. a separator, and a PC/water solution of LiTFSI as the driving electrolyte, exhibited a smooth electrochemical stretching and most suitable for small applications.