Two series of cationic polyacrylamides (C-PAM) were prepared, with and without fluorescent labelling, one with constant charge density (CD:1.4 meq/g) and different molecular weights (MW:2×104, 4×105 and 8×106) and one with constant molecular weight (4×105) and different charge densities (CD:0.65 meq/g, 1.4 meq/g and 2.5 meq/g) .
The exchange reactions of these C-PAMs on monodisperse polystyrene latex (PSL) and cellulose fibers have been studied using C-PAMs with the same MW and CD except that the pre adsorbed polymers were fluorescently labelled. The first series of experiments was carried out near the saturation level of the pre-adsorbed polymers. For C-PAMs with the highest MW(8×106) no significant exchange could be detected on PSL or on fibers. When C-PAM with the highest. CD (2.5 meq/g) was used a slight exchange occurred on both PSL and fibers . The exchange became more extensive with decreasing MW and CD. The exchange reactions initially proceeded quite rapidly and then slowed down. The initial exchange was more extensive on cellulose fibers than on PSL, probably because of the lower surface CD of the fibers, but it levelled off more rapidly than on PSL. This difference is most probably an effect of the porous structure of the fibers.