Spherical silica particles are produced by spontaneous emulsification when an ethanolic solution of partially hydrolyzed tetraethoxysilane (TEOS) is mixed with water. The driving force for emulsification is the difference in ethanol concentration between the two solutions. For particle synthesis, the process can be divided into the following stages: (1) emulsification, (2) droplet growth through coalescence and (3) droplet gelation. The physical and interfacial properties of partially hydrolyzed TEOS directly determine the relative importance of each of these steps through their influence on phase equilibria, interfacial behavior, and the rate of droplet gelation after emulsification. It is demonstrated that either solid or hollow spherical particles ranging in size from as small as 0.1 to > 50 μm can be produced by altering the degree of TEOS hydrolysis and condensation before spontaneous emulsification.
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