Comparison of conducting polymer actuators based on polypyrrole doped with BF4-, PF6-, CF3SO3-, and ClO4-

Polypyrrole films prepared from aromatic ester solutions of tetrabutyl ammonium tetrafluoroborate (TBABF(4)), tetrabutylammonium hexalluorophosphate (TBAPF(6)), tetrabutylammonium trifluoromethanesulfonate (TBACF(3)SO(3) and tetrabutylammonium perchlorate (TBACIO(4)) exhibited large electrochemical strain (11.2-14.0%) and stress (10.6-22.0 MPa) when cycled between -0.9 V and +0.7 V vs Ag/Ag+ at 2 mV s(-1) and 10 mV s(-1), respectively, in an aqueous NaPF6 solution, amongst which PPy-CF3SO3_ solely elongated mechanically by 60-100%. It is therefore more suitable for practical artificial muscle devices. Although polypyrrole actuators doped with ClO4- exhibited moderate strains for a decade, a PPY-ClO4_- actuator prepared from an aromatic ester solution has showed large electrochemical strain (11.2-13.5%) and stress (12.3-15.2 MPa). When cycled at 100 mVs(-1), polypyrrole actuators exhibited approximately twice as large electrochemical stress as those measured at 10 mV s(-1), because the PPy strip was kept in the doped state (the weakest state) for a shorter time, and early breakage did not occur to give a larger electrochemical stress. Polypyrrole actuators might not be very stable when showing the maximum performance, but the electrochemical strain remained almost constant up to 100 cycles under moderate conditions, such as being driven at 0.1 Hz.