Thermodynamic manipulation of the particle size in the synthesis of spherical silica from a new aspect of interface wettability

In the stöber synthesis of spherical silica, the alcohol/water ratio is normally regarded as the major factor that determines the final particle size of the products, but a solid relationship between the alcohol/water ratio and the particle size is hard to be deduced, and the thermodynamic mechanism behind this phenomenon has not been fully discussed yet. In this paper, the methanol/ethanol/isopropanol-H₂O solvents with different alcohol/water ratio are used to prepare spherical silica particles via a classic stöber synthesis. It is found that not only the surface tension of the reaction system, but also the interface contact angle can effectively influence the final particle size of the silica products, and an interfacial wetting effect could be deduced for the thermodynamic analysis of this phenomenon. In this interfacial wetting mode for the particle size manipulation, the particle size is proportional to the surface tension of the reaction system when the interface contact angle is below 90⁰, but an inverse proportional relationship will be applicable when the interface contact angle is above 90⁰. Assisted with this new mechanism, the iso-particle size contour curves based on pairs of surface tension and the interface contact angle could be deduced, and the controllable stöber synthesis of spherical silica particles could be reached in a more facile and accurate way.