Monodisperse polymer spheres
The Stober method has long been established as an efficient way for making colloidal silica particles of uniform size by the hydrolysis and condensation of Si[(OEt).sub.4] in aqueous solution under mildly basic conditions. In addition to simplicity, the method offers control over particle size and shape. Equally important, it guarantees a narrow size distribution and thus provides monodisperse silica particles.
S. Z. Qiao, G. Q. Lu and co-workers have now extended the StOber method to the preparation of monodisperse phenolic resin particles, which can subsequently been converted into carbon spheres (Angew. Chem. Int. Ed., 2011, 50, 5947).
Like silica, the phenolic resin is formed by a condensation reaction, in this case between resorcinol and formaldehyde, yielding a 3-dimensional disordered network (Figure 1). The choice of base is crucial, and amines or ammonia work fine. The solvent, water or a water-alcohol mixture, is the same as in the formation of silica colloids. Typical conditions for making colloidal spheres with a diameter of 520 [+ or -] 29 nm require an ethanol-water ratio of …
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