Synthesis and phase behaviors of bicontinuous cubic mesoporous silica from triblock copolymer mixed anionic surfactant

Highly ordered mesoporous silicas with bicontinuous cubic structure (space group of Ia3¯d) have been synthesized via a sol–gel route by the condensation of tetraethyl orthosilicate (TEOS) in a mixed surfactant system, poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) triblock copolymer P123 (EO20PO70EO20) mixed with sodium dodecylbenzene sulfonate (SDBS). Small-angle powder XRD, TEM, dynamic light scattering (DLS), and nitrogen adsorption were utilized to determine the phase diagram and illustrate the factors that define the phase boundary lines. The results show that the bicontinuous cubic Ia3¯d mesophase can be reproducibly obtained in a large phase area in the acid concentration–temperature phase diagram, which is induced by anionic surfactant SDBS. A mesophase transformation from 2-D hexagonal p6mm   to cubic Ia3¯d can be easily observed as the decrease of acid concentration and increase of temperature. The decrease of hydrophilic–hydrophobic ratio (VH/VL) of the mixed surfactant micelles favors the formation of the Ia3¯d mesophase. Furthermore, the Ia3¯d mesophase formed with 3.0 M HCl at 45 °C was found to possess a microtubule morphology with the diameter of 1–3 μm, the wall thicknesses of about 0.5 μm, and length up to hundreds of micrometers.