Syntheses of monodisperse silica spheres (MSS) and monodisperse mesoporous silica spheres (MMSS) were studied focusing on the age of starting solutions, the solvent partitioning, and the surfactant dissolution as unconscious process factors. Aging of clear and transparent starting solutions decreased nucleation and increased the size of MSS, while the aging effect was opposite in the case of MMSS. Alcohols were used as co-solvent for alkoxides and water to dilute them. Partitioning ratio of alcohols was also a factor that changes the sphere size. Even when a surfactant is soluble in water and alcohol to readily form a transparent starting solution, the clusters consisting of solute and solvent molecules or their molecular level dissolution states may vary during aging, and thus could be a factor affecting the nucleation of nanoparticles. Aging of a methanolic solution of tetramethylorthosilicate (TMOS) containing a surfactant (C16TAC; cetyltrimethylammonium chloride) resulted in unfavorable formation of irregular (non-spherical) particles probably due to the interaction between TMOS and a moisture in the surfactant during aging. [Figure not available: see fulltext.].
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