Formation of Silica Nanoparticles in Microemulsions

Abstract

Silica nanoparticles for controlled release applications have been produced by the reaction of tetramethylorthosilicate (TMOS) inside the water droplets of a water-in-oil microemulsion, under both acidic (pH 1.05) and basic (pH 10.85) conditions. In-situ FTIR measurements show that the addition of TMOS to the microemulsion results in the formation of silica as TMOS, preferentially located in the oil phase, diffuses into the water droplets. Once in the hydrophilic domain, hydrolysis occurs rapidly as a result of the high local concentration of water. Varying the pH of the water droplets from 1.05 to 10.85, however, considerably slows the hydrolysis reaction of TMOS. The formation of a dense silica network occurs rapidly under basic conditions, with IR indicating the slower formation of more disordered silica in acid. SAXS analysis of the evolving particles shows that approximately 11 nm spheres are formed under basic conditions; these are stabilized by a water/surfactant layer on the particle surface during formation. Under acidic conditions, highly uniform approximately 5 nm spheres are formed, which appear to be retained within the water droplets (approximately 6 nm diameter) and form an ordered micelle nanoparticle structure that exhibits sufficient longer-range order to generate a peak in the scattering at q approximately equal to 0.05 A-1. Nitrogen adsorption analysis reveals that high surface area (510 m2/g) particles with an average pore size of 1 nm are formed at pH 1.05. In contrast, base synthesis results in low surface area particles with negligible internal porosity.

Physical properties of α-Fe2O3 nanoparticles fabricated by modified hydrolysis technique

“…The properties of particles change as their size approaches the nanoscale which in turn provides a large surface area. A variety of nanoparticles like SiO 2 , Cu, TiO 2 , ZrO 2 , BaTiO 3 , BaZrO 3 , LiNbO 3 and Fe 2 O 3 are reported in literature (Finnie et al 2007;Qui et al 1999;Li and Wang 1999;Sundaram et al 2007;Niederberger et al 2004;Kang et al 1996). The two main types of the oxides of iron, i.e., magnetite Fe 3 O 4 and maghemite Fe 2 O 3 are considered to be of great interest due to their paramagnetic properties and thus are used in many fields.…”

Silica-Based Nanoparticles: Design and Properties

“…This synthetic process takes more time than the Stöber method. However, the reverse microemulsion method can overcome the limitations of the Stöber method [25,[55][56][57] by producing silica nanoparticles with a uniform size distribution. Furthermore, this method can efficiently dope dye molecules into the silica nanoparticles.…”

Synthesis of glycylglycine-imprinted silica microspheres through different water-in-oil emulsion techniques

“…Spherical glycylglycine templated silica particles were prepared with both acidic and basic pH sol-gel mixture and the diameter of the obtained particles was compared. Finnie et al [19] reported that for the microemulsion synthesis of silica particles, smaller particles were formed using acidic catalysis. Surprisingly, in our study it was found that in some cases smaller particles were obtained with basic pH.…”