SURFACE MODIFICATION BY POLYELECTROLYTE COMPLEXES - INFLUENCE OF MODIFICATION PROCEDURE, POLYELECTROLYTE COMPONENTS, AND SUBSTRATES

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(dia llyldimethylammonium chloride), and copolymers of maleic acid and prop ylene or styrene. PEL complexes (PEG) are formed by a combination of a queous PEL solutions containing definite amounts of charges (n(-), pol yanion; n(+), polycation). The point of zero charge of the PEC depende d 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 wit h the same stoichiometry on the surface as in solution. Changes of the mechanism and a strong enhancement. of the attainable cationic surfac e charge density could be observed by a two-step modification procedur e (variation B). The influence of the surface charge density of the un treated substrates on the extent of surface modification for both vari ations is also described. (C) 1997 John Wiley & Sons, Inc.