Ionic and Zwitterionic Model Macromolecular Surfactants

Micellization of ionically end-capped and diblock copolymers in a selective polar solvent was investigated using small-angle neutron scattering. In the monofunctional case, either the soluble block (sample Q) or the unsoluble block (sample S) is end-functionalized with an ionic group. In the bifunctional case, both chain ends are ionically end-capped with groups of opposite charges, thus leading to a macrozwitterionic block copolymer (sample Z). Results for these model macromolecular surfactants were compared to that of an uncharged block copolymer of identical mass and block sizes (sample H). Large qualitative differences on the scattering curves were observed as a function of the position of the charge on the chain. The aggregation numbers were obtained by fitting data with the form factor of a spherical micelle, showing differences up to a factor of 2. For sample Q, an experimental structure factor was obtained and fitted by that of a monodisperse hard sphere. A structure for the micelles (chain conformation) is proposed, introducing the concept of a bound counterion in case of sample Z.