C. González

Study of nano-emulsion formation by dilution of microemulsions

The influence of different dilution procedures on the properties of oil-in-water (O/W) nano-emulsions obtained by dilution of oil-in-water (O/W) and water-in-oil (W/O) microemulsions has been studied. The system water/SDS/cosurfactant/dodecane with either hexanol or pentanol as cosurfactant was chosen as model system. The dilution procedures consisted of adding water (or microemulsion) stepwise or at once over a microemulsion (or water). Starting emulsification from O/W microemulsions, nano-emulsions with droplet diameters of 20 nm are obtained, independently on the microemulsion composition and the dilution procedure used. In contrast, starting emulsification from W/O microemulsions, nano-emulsions are only obtained if the emulsification conditions allow reaching the equilibrium in an O/W microemulsion domain during the process. These conditions are achieved by stepwise addition of water over W/O microemulsions with O/S ratios at which a direct microemulsion domain is crossed during emulsification. The nature of the alcohol used as cosurfactant has been found to play a key role on the properties of the nano-emulsions obtained: nano-emulsions in the system using hexanol as cosurfactant are smaller in size, lower in polydispersity, and have a higher stability than those with pentanol.

Preparation of structured meso–macroporous silica materials: influence of composition variables on material characteristics

Meso–macroporous silica materials with a well-ordered array of mesopores were prepared from oil-in-water emulsions. The influence of the following three composition variables on material characteristics was studied: the dispersed phase fraction of the emulsion, the concentration of silica used and the concentration of surfactant. The obtained materials were characterized via small-angle X-ray diffraction scattering, scanning electron microscopy, transmission electron microscopy, Hg intrusion porosimetry and nitrogen adsorption–desorption isotherms. A network of structured mesopores was obtained even when using a highly concentrated emulsion (volume of the disperse phase, ϕxa0≥xa00.75). The mesopores network presented a hexagonal arrangement, with mesopore diameters between 4 and 7xa0nm. Non-ordered macropores, with diameters between 50xa0nm and 10–15xa0μm were also present, depending on composition variables. The isotherms were of type IV, typical of mesoporous materials, but at high p/p0 they were the usual shape for the macroporous materials. The possibility of tailoring mesopore and macropore structures by altering in composition variables could extend the application of these materials.

Ion exchange columns for the synthesis of ordered mesoporous materials

Structured mesoporous materials were successfully synthetized using an ion exchange column as protons source. Operating conditions were set in order to obtain mesostructured materials using short operation times. This method opens the door to the industrial synthesis of this kind of materials. The ordered mesoporous materials were obtained using sodium silicate solution as a precursor and poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (EO19PO39EO19 denoted as P84) was used as structure-directing agent. The influence of the composition variables (surfactant and precursor concentrations) was studied. The materials were characterized by TEM, SAXS and nitrogen adsorption–desorption isotherms to determine their specific surface area. A response surface was obtained, showing that in the studied range the ratio sodium silicate:water was the most significant parameter in order to obtain the materials with a well-structured pore arrangement. The use of sodium silicate solution as silica source instead of TEOS or TMOS, and the possibility of obtaining a material through an ion exchange column are important from the application point of view because of the relatively cheap raw materials and equipments. Presented results indicate that for every precursor:water:surfactant system an optimum experimental operating conditions must be selected once the reactants flow rate has been set.