Surface modification by polyelectrolyte complexes: Influence of different polyelectrolyte components and substrates

The complex formation between oppositely charged polyelectrolytes (PELs) and their interaction with inorganic particles have been investigated. The PELs studied were poly(ethyleneimine)s differing in their molar masses, poly(diallyldimethylammonium chloride) and copolymers of maleic acid and propylene or styrene. To obtain comprehensive information, the results of PEL titration, electrophoretic mobility investigations and scanning force microscopy measurements are compared. Polyelectrolyte complexes (PECs) are formed by combination of aqueous PEL solutions containing definite amounts of charges (n(-), polyanion; n(+), polycation). The point of zero charge of the PEC depended on the selection of different PELs. Changing the molar ratio n(-)/n(+) permitted the preparation of non-stoichiometric polyelectrolyte complexes (nPECs) showing differences in the residual amount of charge and the zeta potential. The nPEC carrying cationic excess charges was used to modify the surface of silicate powders. In contradiction to the adsorption of polycations, nPECs were able to generate a strongly cationic surface charge in most of the cases. It is concluded that the preformed PEC adsorbs roughly with the same stoichiometry as in solution on the surface, but the efficiency of surface modification is quite different for nPECs made from altered PELs. We believe that steric factors of the PELs are responsible for the conformation of the PECs and also for the flexibility with which the complexes rearrange on the surface. The influence of the surface charge density of the bare substrates on the extent of surface modification by PEC is also described. (C) 1997 Elsevier Science B.V.