Morphosynthesis of nanostructured polymer gels by polymerization within reverse hexagonal mesophases

Free radical polymerization of divinyl benzene (DVB) and styrene (St) was performed within reverse hexagonal phases of the anionic surfactant bis(2-ethylhexyl) sulfosuccinate sodium salt (AOT). The morphologies before and after polymerization were studied by small-angle X-ray scattering (SAXS), polarized light microscopy, and scanning and transmission electron microscopy. Polarized light microscopy and SAXS show no significant changes in textures and order during polymerization. A detailed investigation of the polymer matrix after polymerization and removal of the template reveals the formation of regular micrometersized layerlike morphologies. The polymer layers have a hierarchical structure, as they consist of aligned strings of polymer beads with diameters of about 100 nm. Structure formation is directed by the lyotropic phase during polymerization-induced phase separation on a nanometer scale. A mechanism of morphosynthesis is discussed on the basis of characteristic distortions within liquid crystals that are induced by the polymer phase. Parameters such as cross-linking degree and initiator or monomer concentration have a strong influence on the morphologies formed due to a kinetically controlled nucleation and growth mechanism. Finally, the structures formed by polymerization within reverse hexagonal phases are compared to those obtained from lamellar phases of the same surfactant.