engleski

Polyelectrolyte multilayers: properties and applications

Polyelectrolyte multilayers (PEMs) are surface coatings obtained by alternated deposition of positively and negatively charged polyelectrolytes (polycations and polyanions) on a solid surface. It was shown earlier [1] that the PEM buildup strongly depends on various experimental conditions (e.g. ionic strength, type of supporting electrolyte, pH and polyelectrolyte concentration). Answers to some fundamental questions dealing with PEM build-up could be obtained by relating the PEM properties with the properties of corresponding polyelectrolyte complexes (PECs) in solution. Therefore, we compared the results we obtained earlier [2, 3] for the complexation of poly(allylammonium) chloride (PAH) and sodium poly(styrenesulfonate) (PSS) with the results obtained for PAH/PSS multilayer build-up. In order to do so, we studied the formation of PAH/PSS multilayers in aqueous solutions of various electrolytes by means of QCM-D and AFM. The QCM-D measurements indicated the largest deposition was noticed in the case of nitrate and perchlorate anions. This is in accordance with the results obtained for PECs by means of DLS and spectrophotometric experiments which showed anion specific aggregation of positive complexes and the formation of precipitates containing larger amount of PAH with respect to PSS. The thickness of deposited films could be correlated with the complexation enthalpies of used supporting electrolyte ions which provides a path for the modification of multilayer properties simply be changing the type of salt during their preparation. The ions counterbalancing the charge at the surface of PEMs also enable the modification of surface wettability. Since PEMs are promising coatings onto which biomolecules (e.g. proteins, bacteria) could be adsorbed, such studies can enable additional progress in the field of biosensing surfaces and drug delivery.

polyelectrolyte complexes ; polyelectrolyte multilayers ; ionic strength

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