In situ scanning tunneling microscopy study on volume change of polypyrrole/poly(styrene sulfonate)

Volume changes of polypyrrole doped with poly(styrene sulfonate) (PPy/PSS) during redox switching were investigated in an aqueous solution of CsClO4, utilizing electrochemical scanning tunneling microscopy (EC-STM). PPy/PSS was synthesized on a micropatterned Au substrate for the quantitative measurement of volume changes with doping. It was found that the polymer volume is greatly increased due to solvent swelling and the magnitude of anisotropic volume changes during redox switching ranges from −0.95 to 15.5%, depending on the film thickness. The potential cycling between −0.7 and +0.1 V (versus Ag wire) also revealed that the PPy/PSS volume is not linearly related to the potential. The volume decreases with doping up to −0.05 V and begins to rise above −0.05 V.