Polypyrrole films volume change

T. Okamoto, Y. Kato, K. Tada, and M. Onoda, Actuator based on doping/undoping-induced volume change in anisotropic polypyrrole film. Thin Solid Films, 393 (1,2), 383-387 (2001). 

Fig. 7.24 A schematic drawing of an electrochemical triple-layer actuator (polypyr-role C104 nonconducting, double-sided plastic tape polypyrrole) immersed in aqueous LiC104 solution, and the macroscopic movement of the actuator produced due to a volume change in the PP films. (Reproduced from [285] with the permission of Elsevier Ltd.)...

Bahrami-Samani, M., Cook, C.D., Madden, J.D., et al. (2008) Quartz crystal microbalance study of volume changes and modulus shift in electrochemicaUy switched polypyrrole. Thin Solid Films, 516, 9, 2800-7. 

A typical voltammetric response for a polypyrrole film is shown in Fig. 36.3. A correlation can be established between the electric charge consumed to oxidize the polymer and the potential applied at each moment. If the stress gradient at the polymer/polymer interface is linked to the relative change of volume and this is related to the consumed charge, the angle described by the free end of the bilayer will be related to the electric potential. This fact was experimentally confirmed fl6], as can be observed in Table 36.1. The reversibility of the movement is guaranteed by the reversibility of the redox process each position is recovered when the bilayer is submitted to the corresponding potential. 

Changes in volume occurring in polypyrrole during switching have been applied to the fabrication of microactuators and artificial muscles. These systems act as electrochemopositioning devices, with their movements controlled by the applied electrical potential [194,195]. Films of great structural homogeneity are required for this purpose, in order to enhance conformational movements. 

The same electrochemical ion-exchange process makes the polymer change its volume so that polymer films shrink-swell following oxidation-reduction. This suggested their use as actuators and in fact poly(3-octylthiophene) [430] and polypyrrole [431-33] elec-trodeposited onto a gold-coated polyethylene strip makes it bend upon redox switching. 

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