Sol-gel preparation of ultralow refractive index silica coatings with hydroxypropyl-beta-cyclodextrin as porogen

Ultralow refractive index films were prepared based on a base-catalyzed sol-gel process using methyltriethoxysilane (MTES), tetraethylorthosilicate (TEOS) as co-precursors, and hydroxypropyl-beta-cyclodextrin (HPCD) as porogen. After further modification by hexamethylisilazane (HMDS), the lowest refractive index of these silica coatings obtained from the hybrid sol was 1.05 and the static water contact angles of the coatings increased from 66.4 degrees to 128.7 degrees. The effect of weight ratio of HPCD to SiO2 on the refractive index and on the formation of coating films were systematically studied. The data showed that the films prepared with HPCD as porogen got a pore diameter around 4 nm. Compared with those templates such as poloxamer (F127), HPCD not only perform well in decreasing the refractive index of films, but also eliminate light scattering caused by mesopore of the film, will have potential value in the field of surfactant-templated methods. (C) 2016 Wiley Periodicals, Inc.