화학공학소재연구정보센터
Journal of Physical Chemistry B, Vol.105, No.39, 9395-9405, 2001
Volume change in polypyrrole studied by atomic force microscopy
The electrochemically induced volume change in conjugated polymers is of interest for actuator applications. Important parameters include the magnitude and speed of the volume change and how volume correlates with potential and current. In this paper, atomic force microscopy was used to examine the expansion and contraction of films of polypyrrole doped with dodecylbenzenesulfonate. The films were photolithographically patterned to allow the scan to start on the substrate, go over the film, and return back to the substrate, giving an absolute height measurement. The method is described in detail. This, technique allowed us to map the real-time volume change in-situ in the out-of-plane direction, which revealed that the film thickness increased by over 35% in the reduced state compared to the oxidized state. This compares with an inplane strain of similar to2% found in prior studies using bilayers, showing that the volume change is anisotropic. The thickness change was well-correlated with the cyclic voltammograms, and the polymer responded with a 3%/s expansion for an applied reducing potential step. The height change depended on film thickness, with films near 1.5 mum undergoing the greatest strain. The morphologies of the as-grown, oxidized, and reduced states were also examined, but there were no substantial differences. The unexpectedly large out-of-plane strain was confirmed by in-situ mechanical surface profilometry. These measurements also showed that the hardness of the reduced state was lower than that of the oxidized state.