Concentric Circular Approach in Mesoporous Silica Transition Process from Hexagonal to Vesicular Structure

We studied the synthesis of mesoporous silica from cetyltrimethyl ammonium bromide(CTAB) and sodium dodecyl sulfate(SDS) at different molar ratios(R). X-ray diffraction(XRD), scanning electron spectroscopy (SEM), transmission electron spectroscopy(TEM) and nitrogen sorption analysis were then used to further investigate the internal relationship among different morphologies and structures, as well as the mechanism of the transition from hexagonal to vesicular structure. The results reveal that as R increased, a consistent and gradual transition occurred via a concentric circular secondary structure formed. The antagonistic effect between the decreasing curvature of surfactant micelle and increasing curvature of secondary structures may be the reason for the complex morphologies synthesized, and the increasing bending energy ΔG_b is the main driving force for the transition.