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Ionic strength and counteranion type influence on formation of PAH/PSS multilayers and correlation with polyelectrolyte complex formation in solution

The formation of polyelectrolyte multilayers of polyallylammonium cation (PAH) and polystyrenesulfonate anion (PSS) was investigated in aqueous solutions of sodium electrolytes (NaX, X = F, Cl, Br, I, NO3, ClO4) at 25 °C by means of quartz crystal microbalance with dissipation monitoring (QCM-D). The obtained results were compared with the results of polyelectrolyte complexation in solution. The QCM-D measurements indicated that increase in ionic strength led to larger thickness of deposited layers and assymetric incorporation of polymers into nanoassemblies (the amount of polycation was higher than that of polyanion). Anions influenced the film thickness at higher ionic strengths considerably. The largest deposition of material was noticed in the case of nitrate and perchlorate anions. This is in accordance with DLS and spectrophotometric experiments in which anion specific aggregation of positive colloid complexes and the formation of precipitates containing larger amount of PAH with respect to PSS was observed. The complexation enthalpies were also correlated with the thickness of deposited films, following the Hofmeister series. The more enthalpically disfavourable complexation process in solution was, the larger was the amount of material deposited. The results can be explained by different counteranion distributions around polycation, caused by differences in the corresponding hydration enthalpies.

polyelectrolyte multilayers ; polyelectrolyte complexes ; quartz crystal microbalance ; Hofmeister series

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