Kinetically controlled formation of helical mesoporous silica nanostructures correlated to a ribbon intermediate phase

We report here the synthesis of mesoporous silica nanostructures simultaneously having helical morphology and c2mm symmetry correlated to a ribbon intermediate phase. A mixture of four types of helical nanostructures, including short-pitch (just a few lattice constants) sphere-like nanoparticles, short-pitch straight nanorods, long-pitch (hundreds of nanometres) twisted nanorods and long-pitch spiral nanorods could be produced. A formation mechanism was proposed based on the in situ small-angle X-ray scattering (SAXS) measurements and other analyses, with the emphasis on the influences of the assembly kinetics on the structural and morphological properties of the helical nanostructures. Based on the mechanism, we further showed simple kinetic control to prepare solely short-pitch or long-pitch helical nanostructures. The present study demonstrates the possibility to tailor the helical mesostructures through kinetic control and offers prospects for the design and preparation of these types of materials.