Stabilization of [poly(allylamine)–tannic acid]n multilayer films in acidic and basic conditions after crosslinking with NaIO4

Abstract

Thin films containing polyphenols offer great perspectives in terms of biomedical applications and as nano-reactors owing to the ability of polyphenols to reduce metallic cations or to form coordination complexes with them. In this report it is shown that films made from the alternated adsorption of a weak polyelectrolyte, poly(allylamine), and tannic acid which are intrinsically instable at low and high pH values can be made pH insensitive, at least from pH = 1 to pH = 13 by a single contact with a 10 mM sodium periodate solution. IO₄⁻ anions oxidize tannic acid which then reacts with the amino groups of poly(allylamine) to yield covalent bonds between them. In addition, the permeability of the (PAH–TA)_n films for the anionic redox probe hexacyanoferrate is dramatically reduced upon reaction with IO₄⁻ without affecting the film morphology.