Novel processing for improving monodispersity of ceramic spheres and colloidal crystallinity

We recently proposed that an aging of starting solutions for ceramic nanoparticles synthesis can be a factor to control the nucleation of the nanoparticles. Silica spheres are the most suitable material to learn the aging effect due to their ease to handle and their definite shape that can be measured accurately. The size and the uniformity (or, monodispersity) of silica spheres are essentially enhanced with aging time of several days. In this work, a series of colloidal crystal (opal) films were prepared from variously monodispersed silica spheres. The starting solutions (an ethanolic solution of tetraethylorthosilicate and that of ammonia water) were aged for a week or so, and then reacted. Besides the aging method, spheres with slightly different size were mixed into commercial spheres at different ratio to change the monodispersity. For efficient crystallization on substrate we used three methods, namely, natural drying, silicone oil-covered drying and dip-coating. Among these, silicone oil-covered drying and dip-coating processes showed similar high crystallinity, which we defined from the transmission spectrum of the film. Relationship between the monodispersity of spheres and the opal crystallinity was found to be in a single exponential curve for a variety of silica suspensions.