Surface modification by polyelectrolyte complexes: Influence of modification procedure, polyelectrolyte components, and substrates

Abstract

The complex formation between oppositely charged polyelectrolytes (PEL) and their interaction with negatively charged silicate powders have been investigated. The PEL studied were poly(ethyleneimine)s, poly(diallyldimethylammonium chloride), and copolymers of maleic acid and propylene or styrene. PEL complexes (PEC) are formed by a 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 PEL. Changing the molar ratio n―/n + permitted the preparation of nonstoichiometric PEC (nPEC). Preformed cationic nPEC were used to modify the silicate powders (variation A). The nPEC were able to generate a strongly cationic surface charge in most cases. It is concluded that the preformed PEC adsorbs roughly with the same stoichiometry on the surface as in solution. Changes of the mechanism and a strong enhancement of the attainable cationic surface charge density could be observed by a two-step modification procedure (variation B). The influence of the surface charge density of the untreated substrates on the extent of surface modification for both variations is also described.