Layer-by-layer deposition of tannic acid and Fe3+ cations is of electrostatic nature but almost ionic strength independent at pH 5

The step-by-step assembly of tannic acid (TA) and of Fe3+ cations allows to produce films of controlled thickness using exclusively small multivalent ions. In the present investigation, it is shown that even if electrostatic interactions are dominant over ligand to metal charge transfer interactions in stabilizing such films, those electrostatic interactions display a small sensitivity to concentration in NaCl used as a supporting electrolyte as well as to the concentration in sodium acetate in the absence of NaCl. This finding highlights the strong stability of the films obtained through the step-by-step deposition of TA and Fe3+ cations. Complementarily, the films made from 6 deposition cycles of TA and Fe3+ cations do not form Prussian Blue when put in contact with hexacyanoferrate anions. This shows that Fe3+ is so tightly bound to the film that it is not able to form a coordination polymer with Fe(CN)(6)(4-) anions. (C) 2015 Elsevier Inc. All rights reserved.