Surface modification by polyelectrolyte complexes

Co-operative interaction between water-soluble polymers has been a topic of investigation world-wide because of their importance from both scientific and practical viewpoint. Our work is focused on the investigation of complex formation between oppositely charged polyelectrolytes and the interaction with inorganic fine particles for example negatively charged quartz powder and silicic acid. The cationic polyelectrolytes tested were poly(diallyldimethylammoniumchloride) (PDADMAC) and polyallyl-amine (PAA), differing in the molar mass, the molecular geometry and charge density. The anionic polyelectrolytes used were copolymers of maleic acid with propylene (MS-P), stryrene (MS-Sty) and methylstyrene (MS-alpha-MeSty). Two different principles of surface modification with polyelectrolyte complexes were tested. On the first hand previous prepared non-stoichiometric complex dispersions carrying cationic excess charges were contacted to the substrate and on the other hand the polycation was preadsorbed on the oppositely charged surface before an equimolar amount of polyanion was added. Both methods show different results in the reachable surface charge. It is important to note that a synergistic effect with respect to the cationic surface charge was found in dependence on the surface charge density of the substrate, the chosen polyelectrolyte combinations and the used modification procedure. From the results it is concluded that steric factors of the polyelectrolytes are responsible for conformation and stoichiometry of the formed polyelectrolyte complexes and thus the effectiveness of charge modification with polyelectrolyte complex is also determined by the characteristics of the used polyions.