Swelling and contraction of ferrocyanide-containing polyelectrolyte multilayers upon application of an electric potential

We developed a new platform at the interface of polyelectrolyte multilayers (PEMs) and electroactive polymers (EAPs) by combining the easy buildup of PEM thin films and the deformation characteristics of the EAPs. The PEM films were made of poly(L-glutamic acid) (PGA) and poly(allylamine hydrochloride) (PAH). After [Fe(CN)6]4- ions (FCIV) were added, cyclic voltammetry (CV) was performed, resulting in a reversible expansion and contraction of the film. The shape change as well as the film buildup prior to the cycling were monitored in situ using the electrochemical quartz crystal microbalance with dissipation monitoring (EC-QCM-D). Electrochemical atomic force microscopy (EC-AFM) images confirmed the rapid shape deformation. The process takes place in an aqueous environment under mild conditions (maximum potential of 600 mV and no pH change), which makes it a promising tool for biomedical applications. In addition, the electrochemically active films are produced using the layer-by-layer (LbL) method that is already established in biotechnology and biomaterials science; therefore, the presented approach can be readily adapted in these areas, bringing about a new possibility for the nanoscale dynamic control of coating thickness in various applications.