Changes in the interaction characteristics of polyelectrolyte complex covered silica surfaces

The adsorption of polyelectrolyte complexes, PEG, made from the cationic po ly (diallyldimethylammonium) chloride (PDADMAC) and the anionic maleic acid -co-propene copolymer (MA-P) on a Si-wafer surface has been studied. The ap plication of highly diluted colloidally dispersed PEC solutions led to the deposition of single PEC particles onto the surface of the Si-wafer. The in teraction forces of the heterogeneously covered surface were monitored by d irect force measurements with an atomic force microscope (AFM) in the force volume mode. On the surface of a single PEC particle drastic changes in th e interaction forces were found in comparison with the unmodified Si-wafer: in all force vs, distance curves a strong increase of the adhesion was mea sured that can be attributed to the formation of eletrostatic bonds between the negatively charged Si3N4-tip and the cationic excess charge of the PEG . Additionally, the behavior during approach of both surfaces has been dist inct: at pH 6.1 we see a long range electrostatic attraction between the ti p and the PEC particle. The attraction becomes even stronger at pH 4.1, bec ause of an increased positive net charge. Generally, a heterogeneous surfac e with a wide variety of interaction features can be created by the adsorpt ion of PEC particles. (C) 2000 Elsevier Science B.V. All rights reserved.