Preparation of monodisperse silica particles with controllable size and shape
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The effects of dilution of tetraethyl orthosilicate (TEOS) with ethanol on the shape and monodispersity of silica particles were investigated. The results indicated that the dilution of TEOS with ethanol can depress the formation of new nuclei and the aggregation or adhesion of particles and make the distillation of TEOS unnecessary to achieve monodispersed silica spheres. A seeded growth technique using continuous drop addition of TEOS diluted with 4× volume of ethanol was developed to improve monodispersity and spheric shape and increase the size of silica particles. The monodisperse silica particles (150 nm ± 5%–1.2 m ± 1%) with fine spheric shape were successfully synthesized by the seeded growth technique. Using the homemade 280 nm ± 2.8% silica spheres, we prepared opals of high quality which showed periodically ordered packing and a photonic band-gap effect.
I. INTRODUCTION
Monodispersed colloidal particles with uniform size, shape, and composition have wide application not only in the field of physical chemistry dealing with dynamic behavior and stability of particulate systems1 but also in industries including pigments, pharmacy, photographic emulsions,2 ceramics,3 chromatography,4 and catalysts.5 Recently, monodispersed silica colloidal particles have been extensively used to prepare three-dimensional photonic crystals.6 Kolbe7 first found the formation of monodispersed silica particles through the hydrolysis and condensation of tetraethyl orthosilicate (TEOS) in a mixture of alcohol, water, and ammonia. Since then many other researchers have made improvements to the hydrolysis method.8–12 It is now recognized that this approach is the simplest and most effective route to synthesize monodispersed silica spheres.6 However, there still exist some problems to be resolved in the hydrolysis method. First, distilling of reactant-TEOS is needed before use.8–10 Second, a quick addition of TEOS into the mixture of alcohol, water, and ammonia is required for the uniform hydrolization of TEOS to get monodispersed silica spheres. However, the transmission electron microscopy (TEM) images show that the spheres with undesired size and peanut shape caused by aggregation or adhesion of particles cannot be avoided.8–12 Third, in the reported seeded growth technique,10 the addition interval of TEOS is 8 h, which leads to long growth period. a)
Address all correspondence to this author. J. Mater. Res., Vol. 18, No. 3, Mar 2003
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In this paper, the effect of dilution of TEOS (to be added into the mixture of ethanol and ammonia) with ethanol on the shape and monodispersity of silica spheres was investigated. It is found that the growth of silica spheres with undesired size or shape can be suppressed by the dilution of TEOS with 4× volume of ethanol. This makes the distillation of TEOS unnecessary to obtain monodispersed silica spheres. In addition, a seeded growth technique has been developed to improve monodispersity and spheric shape and increase the size of silica pa
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