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Time-resolved specular neutron reflectivity measurements are presented and interpreted for electroactive polyvinylferrocene (PVF) films subject to potentiodynamic electrochemical control. New data acquisition methodology allows an effective measurement time scale on the order of seconds, which is an improvement over conventional methodology by 2 to 3 orders of magnitude. Reflectivity profiles were obtained for PVF films exposed to aqueous 0.1 M NaClO4 in which PVF films are thermodynamically permselective, with contrast variation via H2O and D2O. Irrespective of any model, the raw profiles show chemically reversible film "breathing" due to redox-driven solvent entry and exit during polymer oxidation and reduction, respectively. Modeling reveals three compositionally distinct regions within the polymer film: interfacial regions at the electrode and solution interfaces and a "bulk" interior. The new methodology, supported by simultaneous in situ visible transmission spectroscopy, reveals an unprecedented level of insight into the temporal and spatial mechanistic details of film solvation changes, including a two-stage (de)solvation mechanism for redox switching, differences in interior (in)homogeneity for reduced and oxidized films, and permselectivity failure under dynamic electrochemical conditions for the reduced (but not oxidized) state, in contrast to static conditions that allow permselectivity for both states.

In situ neutron reflectivity measurements have been made on spin cast polyvinylferrocene (PVF) films maintained under electrochemical potential control. The data show that the interiors of both oxidized and reduced films are close to homogeneous. The results show that neutron reflectivity measurements, including isotopic substitution, can provide novel insights into film composition and structure at the electrode/polymer/solution interface. Isotopic substitution of the solvent has allowed the contributions of the solvent and the solute to the total film composition to be separated. Responses were determined to variations in the imposed potential (a constraint at the electrode/polymer interface) and the electrolyte concentration (a constraint at the polymer/solution interface). Solvent entry occurs upon oxidation, resulting is a more diffuse polymer/solution interface. Only at very high concentrations is salt permeation into PVF films sufficiently high to be considered as a possible source of co-ions for r...