From cylindrical-channel mesoporous silica to vesicle-like silica with well-defined multilamella shells and large inter-shell mesopores

Highly regular vesicle-like silica consisting of concentric shells of silica and voids in alternation have been prepared in a multilamellar vesicles (MLVs) template created with a P123 surfactant and a hydrophobic additive 1,3,5-triisopropylbenzene (TIPB) by hydrolysis and condensation of tetraethoxysilane (TEOS). It is shown that the morphology of the mesoporous silica is mainly controlled by the molar ratio of TIPB : P123. Cylindrical-channel (rod-like) mesoporous silica with hexagonal structure was obtained at low molar ratio of TIPB : P123, while a vesicle-like mesoporous silica was prepared at high molar ratio of TIPB : P123. TIPB at low concentration was merely dissolved into the hydrophobic core of the P123 cylindrical micelle, but it was forced to spread into the palisade layer at high concentration and ultimately transformed the cylindrical micelle phase into the MLV phase. The key role of TIPB has been demonstrated in increasing the average packing parameter (P) of P123, and this opens the way to synthesize vesicle-like silica simply by controlling the molar ratio of TIPB : P123.