Predictive synthesis of ordered mesoporous silica with maltoside and cationic surfactants based on aqueous lyotropic phase behavior

Self-assembled nonionic alkyl glycoside surfactants are of interest for creating functional adsorption and catalytic sites at the surface of mesoporous sol–gel-derived materials, but they typically impart poor long-range order when they are used as pore templates. Improved order and control over the functional site density can be achieved by mixing the alkyl polyglycoside surfactant with a cationic surfactant. Here, we investigate the rarely reported lyotropic liquid crystalline (LLC) phase behavior of aqueous solutions of a nonionic disaccharide surfactant, n-dodecyl-β-d-maltoside (C12G2/DM), and cetyltrimethylammonium bromide (C16TAB) by low-angle powder X-ray diffraction (XRD) and polarized optical microscopy (POM). An approximate ternary phase diagram of the C16TAB–C12G2–water system is developed at 50 °C, which includes 2-D hexagonal (P6mm symmetry), bicontinuous cubic (Ia3¯d symmetry), lamellar, and rectangular (cmm symmetry) LLC phases. By replacing the volume of water in the phase diagram with an equivalent volume of silica, ordered mesoporous materials are prepared by a nanocasting technique with variable C12G2/C16TAB ratios. For large regions of the phase diagram, this approach is predictive. However, silica materials synthesized with comparatively high C12G2/C16TAB ratios are only poorly ordered in a way that does not correspond to their lyotropic liquid crystalline phase behavior. Also, in contrast with our previous study of mixed C16TAB/n-octyl-b-d-glucopyranoside templating [37] the boundary between hexagonal and bicontinuous cubic materials is shifted towards higher surfactant content than in the aqueous LLC system.

The ternary lyotropic liquid crystal phase diagram of n-dodecyl-β-d-maltoside, cetyltrimethylammonium bromide and water predicts the mesostructure of silica/surfactant materials except in the shaded regions.Figure optionsDownload high-quality image (86 K)Download as PowerPoint slide