Synthesis of Mesoporous Silica Particles and Capsules by Miniemulsion Technique

Abstract

Mesoporous silica particulate structures of different morphologies from particles to capsules have been prepared by combining the sol-gel process with the cooperative self-assembly in inverse miniemulsion. We report a novel synthetic approach at room temperature, with low surfactant concentrations (5 and 10 mol %, relative to the precursor), and a short synthesis time of only a few hours. As a precursor, glycol-modified silane (tetrakis(2-hydroxyethyl)orthosilicate, EGMS) is used, which shows the advantage of being highly water-soluble. The precursor (EGMS) and the structuring surfactant (cetyltrimethylammonium bromide, CTAB) were dissolved in hydrochloric acid and dispersed in a mixture of hydrocarbons (Isopar M) by ultrasonication. In this synthesis, two different surfactants were used simultaneously. One surfactant (CTAB) acts as a lyotropic template, whereas the second surfactant is an amphiphilic block copolymer (PE/B-b-PEO) that stabilizes the droplets. For template removal, the final material was calcined. The obtained materials were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and nitrogen sorption (Brunauer-Emmett-Teller (BET) methodology). The effect of synthesis conditions such as the amount of templating surfactant (CTAB), the temperature during ultrasonication, the reaction time, the pH value, and the amount of stabilizing surfactant (PE/B-b-PEO) on cooperative self-assembly, morphology, and specific surface area were investigated. Shortly after ultrasonication, porous particles a few hundreds of nanometers in size are formed, which are transformed to capsules and finally to porous flakes with increasing reaction time. This transformation is strongly influenced by the amount of stabilizing surfactant (PE/B-b-PEO). By simply varying the amount of PE/B-b-PEO, the morphology and mesostructural ordering, as well as the porosity, can be tuned over a wide range.

Ordered meso-/macroporous silica and titania films by breath figure templating in combination with non-hydrolytic sol–gel processing

“…A similar trend has been observed by Landfester et al for a miniemulsion-assisted synthesis of mesostructured silica particles [20]. During the synthesis (by a combination of an inverse miniemulsion approach with solegel processing and templating via cooperative self-assembly), they obtained either porous particles or hollow capsules.…”

Characterization of a Polyamine Microsphere and Its Adsorption for Protein

“…Each droplet can be used as an independent nanoreactor under preservation of droplet size, droplet number, and concentration in each droplet [26]. When emulsion droplet is used as the vessel or template for polymerization, the size and shape of product are determined [27].…”

Biphasic synthesis of colloidal mesoporous silica nanoparticles using primary amine catalysts

“…Recently, Urata et al [23,24] developed a dialysis process for the removal of surfactants while retaining the dispersion of MSNs. MSNs can also be prepared by aerosol-assisted self-assembly [25] and miniemulsion [26] techniques, where each droplet acts as a microreactor for controlling the particle size. Although the formation of MSNs has been achieved in the above examples, synthesis of discrete MSNs with long-term colloidal stability and excellent hydrothermal stability still remains a challenge.…”