Adsorption of bilayers and multilayers of cationic and anionic co-polymers of acrylamide on silicon oxide

Abstract

Silica surfaces were consecutively treated with copolymers of cationic and anionic polyacrylamides (C-PAM and A-PAM, respectively) and the layer-by-layer build-up was continuously monitored with the aid of stagnation point adsorption reflectometry (SPAR). Four different charge densities of the cationic polymer and one charge density of the anionic polymer were studied. The solid substrate used in the investigation was an oxidized Si wafer, the charge of which was varied by performing the measurements at different pH. Adsorption measurements were performed both in deionized water and with a background electrolyte concentration of 0.01 M NaCl. The results show that the adsorption of C-PAM at pH 6 was dominated by electrostatic interactions. However, a significant nonionic contribution to the adsorption of C-PAM on SiO(2) was detected-when the results of adsorption measurements conducted in deionized water and in 0.01 M NaCl were compared. At pH 9, the adsorption of C-PAM onto SiO(2) was found to be geometrically restricted since the adsorption stoichiometry between the polymer charges and the charges on the surface was less than 1 irrespective of the charge of the C-PAM. Adsorption of the A-PAM onto the C-PAM covered surface increases as a function of the adsorbed charges in the first layer. Experiments showed that it was possible to form multilayers of polyelectrolytes on the SiO(2) surface provided the charge of the C-PAM was high enough. The critical charge of the polyelectrolyte for the formation of multilayers was also dependent on the charge of the substrate; that is, the lower the surface charge the higher the critical charge of the C-PAM. The substrate affected the amount of polyelectrolyte adsorbed up to the fifth layer. For further layers there was almost a stoichiometric relationship between the charges of the polyelectrolytes in consecutive layers. Results from studies of the formed multilayers with a quartz crystal microbalance (QCM-D) indicated that there was a close correlation between energy dissipation into the multilayers and a decrease in the adsorption as detected with SPAR. This in turn indicates that a decrease in the reflectometer signal does not necessarily indicate a decrease in adsorption.

Comparison of FBAR and QCM-D sensitivity dependence on adlayer thickness and viscosity

“…On the other hand, the dissipation increased after PGA and decreased after PAH addition in accordance with the literature (Wagberg et al, 2004;Boulmedais et al, 2003;Grieshaber et al, 2008). This indicates a more rigid film in case of PAH being added the last (Figure 3a).…”

Mass and charge balance in self-assembled multilayer films on gold. Measurements with optical reflectometry and quartz crystal microbalance

“…So-called linear [4] or exponential [5,6] growth rates were frequently described from the change of output in different analytical measurements, but they were scarcely discussed in terms of mass uptakes, due to difficulties in scaling the instrumental output. In the case of charge densities, results cover a wide range between approximately a 1/1 polymer stoichiometry [7,8] three fold excess of the cationic polymer [9] for the same polymers pair as in Ref. [7], and intermediate cases [10].…”

The influence on paper strength properties when building multilayers of weak polyelectrolytes onto wood fibres

“…Despite the fact that the theory and subsequent conversion of raw data to adsorbed amount are based on a one-layer adsorption model, it has previously been shown that optical reflectometry can yield valuable information on the kinetics of PEM formation [8,20,21]. A full description of the equipment and the underlying theory of its use is given by Dijt et al [22].…”