Polyoxometalates in Polyelectrolyte Multilayer Films: Direct Loading of [H7P8W48O184]33- vs. Diffusion into the Film

The immobilization of polyoxometalates (POMs) into thin organized films is of major importance for the development of functional devices like electrochromic films and catalysts. We investigate herein two methods to incorporate the wheel-shaped tungstophosphate [H7P8W48O184](33-) (P8W48) polyoxometalates (POM) into polyelectrolyte multilayer (PEM) films, which offer the advantage of controlled thickness and ease of processability. The first method, whose feasibility has been widely demonstrated, consists in the alternate deposition of a polycation and the negatively charged POM. The second method has never been used to load POMs into thin films: an exponentially grown polyelectrolyte multilayer film, made from sodium hyaluronate (HA) and poly-L-lysine (PLL), is brought in contact with the POM solution to allow its passive diffusion into the PEM film. Both methods of incorporation are compared in terms of effective POM concentration in the film. In addition it is shown that the second method leads to a maximum in the amount of incorporated POM as a function of its concentration in solution. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)