engleski

Linear vs. Exponential Growth of Polyelectrolyte Multilayers ; an Optical Reflectometry Study

It is known that the formation of multilayers of polyelectrolytes of alternating charge can be followed in situ by means of stagnation point optical reflectometry [1, 2]. In this study, the abovementioned method was applied for investigations of the distinction between linear and exponential (or superlinear) build-up mechanisms of polyelectrolyte multilayers with special emphasis on the influence of ionic strength of solution on such process. In our experiments we used two typical pairs of polyelectrolytes known in the literature for predominantly linear (poly(allylamine hydrochloride) / poly(sodium 4-styrenesulfonate)) and exponential (poly-L-lysine hydrochloride / poly-L-glutamic acid) growth. As the solid substrate, we used silica in the form of silicon wafers carrying an oxide layer. We investigated the formation of polyelectrolyte multilayers in both systems at different ionic strengths and in the presence of different salts. As the supporting electrolyte we used potassium chloride and potassium nitrate. We observed that in both investigated systems the ionic strength significantly influences the growth pattern. In the PAH/PSS system, at lower ionic strength (e.g. 10 mM) the growth is approximately linear and at higher Ic (e.g. 300 mM) the growth is exponential. On the other hand, when we analysed the PLL/PGA system, at all investigated ionic strength the formation of multilayers was characterized by exponential growth. Additionally, the obtained results were compared with the results obtained earlier for the formation of multilayers in other systems.

polyelectrolyte multilayers ; optical reflectometry ; exponential growth ; linear growth

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