Adsorption of charged block copolymers with two adsorbing blocks

Abstract

We have investigated the adsorption of diblock copolymers consisting of uncharged water-soluble dihydroxypropyl methacrylate (HMA) and positively charged dimethylaminoethyl methacrylate (AMA) on TiO2 and SiO2. Adsorbed amounts of the block copolymers and of the homopolyelectrolyte 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 find that the adsorption behaviour of charged block copolymers is essentially different from that of neutral block copolymers, because the electrostatic interactions, including an induced interaction, play a key role. This induced interaction influences the dissociation of the surface groups, thereby reducing the build-up of the electrostatic potential on the surface. When the composition of the block copolymer is varied a maximum in the amount adsorbed is observed, which is similar to that found for adsorption of polyelectrolytes with varying segment charge. Also, depending on the pH, charged block copolymers can be adsorbed with both blocks in contact with the surface, whereas neutral block copolymers usually have one anchoring block.Qualitative agreement is found between the experimental and theoretical results.