Formation and thermal-induced changes of mesostructures in fluorinated organosilicate films

Mesoporous fluorinated organosilicate films were synthesized from tetramethoxysilane and perfluoroalkylsilanes (RO)3Si-R′ under acidic conditions in the presence of cationic surfactant or triblock copolymer by sol–gel spin-coating. The mesoporous fluorinated organosilicate films made from perfluoroalkylsilanes (PFASs) with long perfluoroalkyl chains, which acted as a template, displayed a hexagonal mesostructure with very low concentration of surfactants, regardless of the kind of surfactants. Although most of the surfactants and organic moieties were decomposed above 550 °C, the mesostructure of mesoporous fluorinated organosilicate films was maintained up to 650 °C. After calcination at 550 °C, their composition was similar to that of mesoporous silica films, and the cylindrical mesostructure was changed to less ordered and broken mesostructure when PFASs with long perfluoroalkyl chains were used. However, the cylindrical mesostructure was maintained when PFASs with short perfluoroalkyl chains were used. Therefore, PFASs with long perfluoroalkyl chains acted as a structure directing agent, and the chain length of PFASs affected the formation of mesostructure and thermal-induced mesostructural change. Also, the increase of calcination temperature caused the change of the composition, mesostructure, and optical property in the mesoporous fluorinated organosilicate films.