Microemulsion templates for mesoporous silica

Small-angle neutron scattering (SANS) studies indicate that oil-in-water mi croemulsions, consisting of aqueous HCl, the nonionic block copolymer surfa ctant Pluronic P123 (poly(ethylene oxide)-block-poly-(propylene oxide)-bloc k-poly(ethylene oxide), EO20-PO70-EO20, M-av = 5800), 1,3,5-trimethylbenzen e (TMB, oil), and ethanol (cosurfactant), are novel colloidal templates tha t direct the synthesis of mesoporous silica with well-defined ultralarge po res. The sizes of the microemulsion droplets can be controlled by the TMB c oncentration and by temperature. The microemulsion droplet sizes and the ce ll sizes of the mesostructured cellular foam (MCF) materials increase linea rly with the cube root of the TMB concentration. Increasing the temperature from 40 to 80 degrees C expands the droplet sizes, which is similar to mic ellar solutions of Pluronic surfactants in the absence of oil. Ethanol acts as a cosurfactant, increases the TMB solubility of the P123 micelles, and enables swelling of the P123 micelles. Low concentrations of NH4F (8 x 10(- 3) mol/L) show no significant effect upon the nature of the microemulsions. The polydispersities of the droplet sizes range from 11% to 21%. The micro emulsion templates reported in this paper are considered as a valuable addi tion to existing colloidal templates that direct the synthesis of porous ma terials. The benefits of the microemulsion templates are (i) their easy pre paration by simply mixing water, surfactant, oil, and a cosurfactant, and ( ii) the synthesis of ultralarge-pore mesoporous materials with narrow pore size distributions without the need for further processing.