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The formation of silicate/organic hybrid micelles is an important milestone in the two-step synthesis of mesoporous silica with polyethyleneoxide (PEO) nonionic structure directing agents (C.R. Chimie 8 (2005) 579). Unlike many inorganic/organic hybrid micelles, these objects have the inorganic component as a diffuse layer positioned at the periphery of the initial micelles and interacting with the hydrophilic polyoxyethylene palisade. We studied how this additional inorganic layer can modify the structure and dynamics of micelles prepared with different types of nonionic surfactants using steady-state and time-resolved fluorescence and dynamic light scattering. Our results show that these hybrid micelles still possess a versatile behavior, which allows them to adapt reversibly to temperature changes. This silicate layer tends to stabilize and consolidate the micelle structure, especially close to the cloud point of critical micelle temperature for polypropyleneoxide (PPO)-based triblock copolymers. Their internal structure is only slightly disturbed by the silicate layer, which reduces the molecular exchanges a little bit. Among other results, we managed to elucidate why mesoporous silica prepared with Pluronic P123, according to our synthesis, stands a dramatic structural change from wormhole to hexagonal structure at 40 °C. Our dynamic light scattering study shows that 40 °C is a critical temperature corresponding to a sphere-to-rodlike structural transition of hybrid micelles, which is not observed with pure micelles. [ABSTRACT FROM AUTHOR]

We report how the control of a single parameter, the co-surfactant, determines the phase transitions of oil-in-water swollen liquid crystals (SLCs) prepared with cetyltrimethylammonium bromide (CTAB), from cubic to hexagonal, lamellar, and finally sponge-like structures. SLCs are complex mixtures (surfactant + co-surfactant + water + salt + oil) usually prepared to form hexagonal mesophases, with cell parameters tunable between 3 and 30 nm. These hexagonal mesophases were successfully used as nanoreactors to prepare a broad range of nanostructured materials. Because the potential of these mesophases as adaptive nanoreactors has not been extended to other liquid crystal geometries than the hexagonal, we studied in a first step the structure evolution of SLCs made with CTAB, cyclohexane, pentanol-1, water and different stabilising salts. We used small-angle X-ray scattering (SAXS), polarised light microscopy and Freeze-Fracture TEM to provide a partial phase diagram and list the different mesophases obtained as a function of composition. We report that the adjustment of a single parameter, the co-surfactant (pentanol-1), determines the phase transition between cubic, hexagonal, lamellar, and sponge-like structures, all other parameters such as the nature and concentration of salt, or amount of oil being constant. [ABSTRACT FROM AUTHOR]