Cooperative self-assembly of silica-based mesostructures templated by cationic fluorocarbon/hydrocarbon mixed-surfactants

In this work, we have systematically studied the influences of reaction temperature, silica sources, and nature of surfactant templates on cooperatively self-assembled mesostructures. Both positively charged hydrocarbon (HC) surfactant cetyltrimethylammonium bromide (CTAB) and fluorocarbon (FC) surfactant FC-4 were used as the templates, and four silica sources tetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS), 1,2-bis (trimethoxysilyl) ethane (BTME) and 1,2-bis (triethoxysilyl) ethane (BTEE) were used as the precursors. When CTAB and FC-4 were applied as mixed templates and BTME or BTEE as the silica source, it was found that ordered mesostructure with a hollow morphology can be successfully obtained only at temperatures higher than the demixing temperature (Td) of two surfactants. When FC-4 was used as a single template, generally vesicular structures were obtained regardless of the silica sources. In the case of CTAB/FC-4 co-templates, the utilization of pure silica sources (TEOS and TMOS) gave rise to nano-particles with neither hollow morphology nor the ordered mesostructure. The above results can be understood by the interactions between the templates and the silica sources considering the hydrophobic sequences of surfactants (CTAB < FC-4) and different silica precursors (TMOS < TEOS < BTME < BTEE). It is anticipated that by carefully tuning the interaction between surfactant templates and silica species, novel mesoporous materials with controlled composition, structure and morphology can be designed and fabricated.