Size-tunable silica nanowires prepared using reverse microemulsion-gel systems

Abstract

Abstract Self-assembled hybrid gels were formed by adding amounts of tetraethyl orthosilicate (TEOS) dissolved in water to organic solutions of sodium bis(2-ethylhexyl) sulfosuccinate (Aerosol-OT, AOT). Two kinds of hybrid gels were prepared and discussed in this study. In the first, gels were prepared through chemical hydrolysis-condensation reactions of TEOS. The growth of a one-dimensional silica network in the confinement of the AOT reverse microemulsions led to gel formation. In the other, gels were prepared through reverse hexagonal mesophases due to high concentrations of AOT. Rheological studies demonstrated that the elastic modulus, G', is greater than the viscous modulus, G, at all frequencies, and G' did not depend upon the frequency in either system, implying they can be used as gels. The gels obtained through silica networks had smaller G' values and higher transformation strains than those gels prepared through AOT reverse hexagonal mesophases. Small-angle X-ray scattering (SAXS) results showed that both systems exhibited cylindrical structures with short-range order, and the radii of the cylinders were significantly influenced by the change of AOT, TEOS and water concentrations. Transmission electron microscopy (TEM) confirmed that silica nanowires were found in both gel systems after removing the AOT components. The length of the nanowires for the gels prepared through silica networks was larger than that for the gels prepared through AOT reverse hexagonal mesophases. This was because the silica grew into a one-dimensional network (axial direction) due to the confinement of the cylindrical structures.