Electrical Stimuli-Responsive Decomposition of Layer-by-Layer Films Composed of Polycations and TEMPO-Modified Poly(acrylic acid)

We previously reported that layer-by-layer (LbL) film prepared by a combination of 2,2,6,6-tetramethylpiperidinyl N-oxyl (TEMPO)-modified polyacrylic acid (PAA) and polyethyleneimine (PEI) were decomposed by application of an electric potential. However, there have been no reports yet for other polycationic species. In this study, LbL films were prepared by combining various polycationics (PEI, poly(allylamine hydrochloride) (PAH), poly(diallydimethylammonium chloride) (PDDA), and polyamidoamine (PAMAM) dendrimer) and TEMPO-PAA, and the decomposition of the thin films was evaluated using cyclic voltammetry (CV) and constant potential using an electrochemical quartz crystal microbalance (eQCM). When a potential was applied to an electrode coated on an LbL thin film of polycations and TEMPO-PAA, an oxidation potential peak (Ep(a)) was obtained around +0.6 V vs. Ag/AgCl in CV measurements. EQCM measurements showed the decomposition of the LbL films at voltages near the Ep(a) of the TEMPO residues. Decomposition rate was 82% for the (PEI/TEMPO-PAA)(5) film, 52% for the (PAH/TEMPO-PAA)(5) film, and 49% for the (PDDA/TEMPO-PAA)(5) film. It is considered that the oxoammonium ion has a positive charge, and the LbL films were decomposed due to electrostatic repulsion with the polycations (PEI, PAH, and PDDA). These LbL films may lead to applications in drug release by electrical stimulation. On the other hand, the CV of the (PAMAM/TEMPO-PAA)(5) film did not decompose. It is possible that the decomposition of the thin film is not promoted, probably because the amount of TEMPO-PAA absorbed is small.