ADSORPTION OF CHARGED BLOCK-COPOLYMERS WITH 2 ADSORBING BLOCKS

We have investigated the adsorption of diblock copolymers consisting o f uncharged water-soluble dihydroxypropyl methacrylate (HMA) and posit ively charged dimethylaminoethyl methacrylate (AMA) on TiO2 and SiO2. Adsorbed amounts of the block copolymers and of the homopolyelectrolyt e AMA were determined by means of reflectometry, as a function of pH, ionic strength and block length ratio. These results are compared with theoretical calculations using the self-consistent-field (SCF) theory of Scheutjens and Fleer extended for charged block copolymers. We fin d that the adsorption behaviour of charged block copolymers is essenti ally different from that of neutral block copolymers, because the elec trostatic interactions, including an induced interaction, play a key r ole. This induced interaction influences the dissociation of the surfa ce groups, thereby reducing the build-up of the electrostatic potentia l on the surface. When the composition of the block copolymer is varie d a maximum in the amount adsorbed is observed, which is similar to th at found for adsorption of polyelectrolytes with varying segment charg e. Also, depending on the pH, charged block copolymers can be adsorbed with both blocks in contact with the surface, whereas neutral block c opolymers usually have one anchoring block. Qualitative agreement is f ound between the experimental and theoretical results.