In this work, we studied the changes in volume of an electroactive polymer as [Os(bipy)(2) (PVP)(10)Cl](2+). The dependence of the polymer volume on the solution pH and applied potential was measured. The morphology of [Os(bipy)(2) (PVP)(10)Cl](2+), deposited onto monocrystalline Si substrates, both by drop coating and by spin coating was studied by AFM. Drop-coated films show a globular structure on top of a thin and homogeneous film while spin-coated films are even and homogeneous. The volume changes with the pH of the external solution were measured following the changes in the globules size of drop-coated films. Also, the thickness dependence of spin-coated films on pH was measured by AFM. Both the size of the globules and the thickness of the films increase as the pH of the external solution decreases. The possible reasons for this increase are discussed. The volume change following the oxidation of a drop-coated polymer was estimated from the projected area obtained by optical microscopy with image capture. The images show an increase in the projected area as the film is progressively oxidized. The possible reasons for this increase in volume are discussed. (C) 2004 Elsevier Ltd. All rights reserved.