Effect of mono- and divalent ions on the formation and permeability of polyelectrolyte multilayer films

- Properties of multilayer films depend on the type of used polyelectrolytes.
- Permeability of multilayer is connected with charge compensation and the nature of a molecule transported through the film.
- With the increasing number of adsorbed polyelectrolyte layers, the permeability decreases.
- Permeability of films is affected by the sign of the electroactive probe contributing in the electrochemical reaction.
- Films with the same number of layers formed in MgCl2 attenuated redox current stronger than one deposited in NaCl.

The layer by layer (LbL) sequential adsorption of oppositely charged polyelectrolytes is a simple tool to form ultrathin multilayer membranes with highly controlled properties. In our studies we have focused on the formation of multilayer films from the pair of synthetic, model polyelectrolytes: poly(allylamine hydrochloride) (PAH)/poly(4-styrenesulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDADMAC)/poly(4-styrenesulfonate) (PSS) in the presence of monovalent (NaCl) and divalent (MgCl2) ions solution with the same ionic strength. Quartz crystal microbalance (QCM) was used to determine the film mass. To examine barrier properties of the multilayers two electroactive probes were selected: positively charged hexaammineruthenium (III) chloride and equimolar solution of potassium hexacyanoferrate (II) and potassium hexacyanoferrate (III) of negative charge. We demonstrated that the mass/thickness of the film was larger when the polyelectrolytes were deposited in the presence of divalent ions. On the other hand, the permeability of the polymer films depended not only on the ionic strength, but also on the valence of the ions in the polyelectrolyte solution as well as the charge of the chosen electroactive probe.

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