Micellar structures of -poly(styrene-b-4-vinylpyridine)s in THF/toluene mixtures and their functionalization with gold

The effects of the block copolymer composition and the solvent selectivity on the micellar morphologies of poly(styrene-b-4-vinylpyridine)s (PS-b-P4VPs) and their functionalizations with gold were studied in 10 mg/mL solutions using small-angle X-ray scattering and transmission electron microscopy (TEM). The solvent selectivity for the PS block was controlled by toluene/tetrahydrofuran (THF) mixtures in which toluene and THF are selective for PS and nonselective, respectively. The micellar structure was strongly dependent on φ (wt % toluene in toluene/THF mixture) and the composition of the block copolymers. PS(12K)-b-P4VP(11.8K) (symmetric) showed spherical micelles in the entire range of φ except φ = 0 (THF, nonselective solvent). PS(3:3K)-b-P4VP(18.7K) (asymmetric, longer P4VP) showed multiple morphologies with transitions from spheres to cylinders and finally to vesicles with an increase in φ. PS(19.6K)-b-P4VP(5.1K) (asymmetric, longer PS) showed spherical micelles only at the narrow ranges of 90 wt % ≤ φ ≤ 100 wt % and an isotropic state at the other ranges. The micelles formed a complex with HAuCl₄ and were reduced with hydrazine in the solvent mixtures. The morphologies of micelles, hybrid micelles, and gold nanoparticles were investigated by using TEM and UV/vis spectroscopy. The possible mechanisms leading to these morphological changes and the formation of the nanosized gold particles were also discussed.