The effect of cationic surfactant and some organic/inorganic additives on the morphology of mesostructured silica templated by pluronics

Abstract

Tri-block copolymers (poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide), represented as EO x PO y EO x ), pluronics (F127 = EO 106PO 70EO 106, P65 = EO 20PO 30EO 20, P85 = EO 27PO 39EO 27, P103 = EO 17PO 55EO 17, and P123 = EO 20PO 70EO 20) and cationic surfactants (cethyltrimethylammonium bromide (CTAB)), two surfactant systems, form complex micelles that self-assemble into mesostructured particles with distinct morphology depending on the pluronic type, the concentration of the cationic surfactant and the organic–inorganic ingredients in a siliceous reaction media under acidic conditions. The CTAB–P65 and CTAB–P85 systems form spheres, CTAB–P103 and CTAB–P123 systems form wormlike particles, and CTAB–F127 system form single crystals of mesostructured silica particles under very similar conditions. However addition of various salts (such as KCl and NaNO 3) into a CTAB–P103 or CTAB–P123 solution system and cyclohexane and KCl into a CTAB–P85 solution system produces the mesostructured silica spheres and wormlike particles, respectively. By controlling the hydrophilic–hydrophobic character of the pluronics, core–corona interface, by means of additives, such as small organic molecules or salts, one could obtain the desired morphology that is dictated by the shape of the micelles of the pluronic–cationic surfactant complex. The effects of the additives and the formation mechanism of those morphologies have been discussed using spectroscopy (FT-IR and Raman), diffraction (XRD) and microscopy (POM and SEM) data.