Layer thickness for high molecular weight cationic polyacrylamides adsorbed on a surface with a preadsorbed poly-diallyl dimethylammonium chloride

The adsorption of two cationic polymers to a silica surface was studied. Fi rst, a highly charged poly-diallyldimethylammonium chloride (poly-DADMAC), 6.0 meg g(-1) with a molecular weight of 1.2 million, was adsorbed and ther eafter a less charged cationic polyacrylamide (C-PAM), 0.42 or 0.97 meg g(- 1) with molecular weights of 7 or 9x10(6). respectively: was added. The ads orbed amounts and layer thicknesses were measured in situ by null ellipsome try. The thickness of the C-PAM layer was shown to be the same even when th e amount of adsorbed C-PAM was reduced due to the preadsorbed poly-DADMAC. A larger total amount of polymer charges was adsorbed to the surface with p readsorbed poly-DADMAC than if only one of the polymers was adsorbed to for m a complete layer. (C) 1999 Elsevier Science B.V. All rights reserved.