Département de chimie moléculaire

Quartz crystal microbalance and cyclic voltammetry are used to study the influence of the supporting salt of polyelectrolyte solns. on the buildup and the structure of PSS/PAH polyelectrolyte multilayers (PSS: poly(4-styrenesulfonate); PAH: poly(allylamine hydrochloride)). This film constitutes a model polyelectrolyte multilayer system. The supporting electrolytes were Na salts where the nature of the anion was changed by following the Hofmeister series from cosmotropic to chaotropic anions (F-, Cl-, NO3-, ClO4-). For all the studied anions, the film thickness increases linearly with the no. of deposition steps. Chaotropic anions lead to larger thickness increments per bilayer during the film buildup than cosmotropic ones, confirming results found on PSS/PDADMA multilayers (PDADMA: poly(diallyldimethylammonium)). Films constituted by {\textgreater}9 PSS/PAH bilayers are still permeable to hexacyanoferrate(II) ions, Fe(CN)64-, whatever the nature of the supporting salt anion. However, these films are impermeable to Ru(II) hexaammine ions, Ru(NH3)62+, after the 3rd PAH layer in the presence of NaF, NaCl, or NaNO3. These results are explained by the presence of an excess of pos. charges in the film, which leads to a pos. Donnan potential. This potential is more pos. when more chaotropic anions are used during the film buildup. Also a film constructed in the presence of chaotropic anions swells and becomes more permeable to Fe(CN)64- ions when the film is brought into contact with a soln. contg. more cosmotropic anions. All the exptl. findings can be explained by a strong interaction between chaotropic anions with the NH3+ groups of PAH that is equiv., as far as the multilayer buildup and electrochem. response is concerned, to a deprotonation of PAH as it is obsd. when the film is constructed at a higher pH. The authors thus arrive to a coherent explanation of the effect of the nature of the anions of the supporting electrolyte on the polyelectrolyte multilayer. Also great care must be taken when studying polyelectrolyte multilayer films by electrochem. probing because electrochem. reactions involving the probes can appreciably modify the multilayer structure. [on SciFinder(R)]