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 I-I). 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.