Controlling the pitch length of helical mesoporous silica (HMS)

The effects of synthesis conditions including the co-structure directing agent (CSDA)/amphiphile molar ratio, reaction temperature, and pH value on the pitch length of the helical mesoporous silicas (HMSs) have been comprehensively investigated. It has been found that the external diameter of the HMS rod increased with increasing CSDA/amphiphile molar ratio, reaction temperature, and pH value, while the pitch length increased linearly with increasing diameter of the HMS rod in a settled condition. The driving force for the formation of HMS has been considered to be the 2d-hexagonally-ordered propeller-like micelles with moment M0 which can be related to the pitch length (p) and diameter (d  ) of the micelle (M0∝dp). The shorter pitch length of the micelle would give rise to a strong moment for the hexagonally-stacked rods in the same micelle diameter, and vice versa with a longer pitch length. It was shown that the moment of the propeller-like micelle was not significantly changed by varying the TMAPS/SDS molar ratio or the pH value, but obviously affected by the reaction temperature.