Preparation of rectangular and 2D-hexagonal mesostructured silica at neutral conditions using poly(oxyethylene) cholesteryl ethers and a water-soluble silica precursor.

We report on the fabrication of hybrid organic-inorganic mesostructured materials from aqueous solutions of a series of poly(oxyethylene) cholesteryl ethers (ChEO(n), where n is the number of oxyethylene units) with a water-soluble silica precursor, tetra(2-hydroxyethyl) orthosilicate (THEOS) at a neutral pH condition. ChEO10 and ChEO15 form rectangular and 2D-hexagonal mesostructures, respectively, as detected by Small-Angle X-ray Scattering (SAXS) measurements. On the other hand, disordered structures (showing nevertheless a correlation length) are observed with longer hydrophilic chain surfactants, such as ChEO20, ChEO24 and ChEO30. Highly ordered mesostructures cannot be obtained at neutral pH when THEOS is substituted with a conventional silica precursor, tetraethyl orthosilicate (TEOS). The structural evolution from initial disordered micellar solutions is dependent on both surfactant and THEOS concentrations. It is also found that the silica mesostructures obtained from ChEO10 and ChEO15 templates are the same as those of the liquid crystalline phases formed in aqueous mixtures of the corresponding surfactant.