IONIC AND ZWITTERIONIC MODEL MACROMOLECULAR SURFACTANTS

Micellization of ionically end-capped and diblock copolymers in a sele ctive polar solvent was investigated using small-angle neutron scatter ing. In the monofunctional case, either the soluble block (sample Q) o r the unsoluble block (sample S) is end-functionalized With an ionic g roup. In the bifunctional case, both chain ends are ionically end-capp ed with groups of opposite charges, thus leading to a macrozwitterioni c block copolymer (sample Z). Results for these model macromolecular s urfactants were compared to that of an uncharged block copolymer of id entical mass and block sizes (sample I-I). Large qualitative differenc es on the scattering curves were observed as a function of the positio n of the charge on the chain. The aggregation numbers were obtained by fitting data with the form factor of a spherical micelle, showing dif ferences 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, introdu cing the concept of a bound counterion in case of sample Z.