Adsorption of cationic, anionic and hydrophobically modified polyacrylamides on silica surfaces

The adsorption of modified polyacrylamides (PAM) at the silica surface has been studied by ellipsometry. To study the influence of the type of modification of the polyacrylamide on the adsorption behaviour, we have used cationic, anionic and hydrophobically modified polyacrylamides with varying charge density and degree of hydrophobisation. The adsorbed amount and adsorbed layer thickness were obtained at a neutral pH and at a constant ionic strength (C-KCl = 0.1 M). The effect of surfactant present during the polymerisation process has also been investigated. Cationic modified polyacrylamides have been found to adsorb most strongly onto the silica surface and a large overcompensation of the surface charge has been observed in all cases. For cationic modified polyacrylamides having additional hydrophobic groups the adsorbed amount decreases with density of hy rophobic groups, and the adsorbed layer thickness is larger. Anionic modified polyacrylamides also adsorb onto the negative silica surface, though the adsorbed amounts are small. The presence of the surfactant Tween 80 leads to an increase in the adsorbed amount for the polymers which adsorb weakly in the absence of the surfactant. However, for the polymers, which have already shown a good ability to adsorb on silica, the addition of surfactant has no significant effect on the adsorbed amount. (C) 2003 Elsevier B.V. All rights reserved.