We describe the redox switching of polyvinylferrocene (PVF) films deposited from CH2Cl2 and sequentially exposed to aqueous solutions of different charge neutralizing anions. The redox-driven population changes and transient fluxes of all mobile species were determined as a function of potential scan rate and film charge state using the electrochemical quartz crystal microbalance. For small spherical anions (BF4-, ClO4-, and PF6-), the fluxes and population changes were not solely determined by the ambient anion; rather, the primary determinant of behavior was the "native" anion that was present during film deposition and initial conditioning. The amount of solvent transferred was controlled by the relative sizes (molar volumes) of the native and ambient anions; this points to a model based upon free volume. The amount of free volume is a function of the molar volume of the native anion. When the films are exposed to solutions of large anions, typified by p-toluenesulfonate and 2-naphthalenesulfonate, and these ions are field-driven into the film, their entry disrupts the structures established by small spherical anions. The mobile species transfer characteristics of the film are then irreversibly altered. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3459903] All rights reserved.