Free-standing gel-like polypyrrole actuators doped with bis(perfluoroalkylsulfonyl)imide exhibiting extremely large strain

Free-standing polypyrrole (PPy) film actuators, prepared electrochemically from aromatic ester solutions of lithium bis(perfluoroalkylsulfonyl)imide (Li(CnF2n+1SO2)(2)N) (n = 1-4) or tetra-n-butylammonium bis(perfluoroalkylsulfonyl)imide (TBA(CnF2n+1SO2)(2)N) (n = 1-2), exhibited extremely large electrochemical strains up to 40% when driven in aqueous or propylene carbonate (PC) solution of the corresponding Li(CnF2n+1SO2)(2)N. PPy doped with (CnF2n+1SO2)(2)N- swelled in some organic solvents such as acetone and PC, and had a spongy macroporous morphology such that large (CnF2n+1SO2)(2)N- anions could go in and out of the film as dopant, resulting in the extremely large strain induced electrochemically. When smaller anions were used for the electrochemical stretching of PPy-(CnF2n+1SO2)(2)N- actuators, an ineffective volume change of PPy was observed, whereas when larger anions were employed, the electrochemical strain was very small as if the PPy actuators showed a 'template effect. PPy films doped with (CF3SO2)(2)N- actuated quickly in H2O/PC mixed solution of Li(CF3SO2)(2)N, exhibiting a maximum strain rate of 13.8% s(-1) and a maximum strain of 33.5%.