Size Monitoring in the Synthesis of Silica Nanoparticles Using Asymmetrical Flow Field‐Flow Fractionation (AF4)

Abstract

Particle size is one of the important parameters that determine the characteristics (and applicability) of silica nanoparticles. An accurate sizing technique is therefore required for quality control during the synthesis of silica nanoparticles. Unlike other sizing techniques, the field‐flow fractionation (FFF) provides size‐based separation of colloidal particles, and allows an FFF elution profile, which can be converted to a size distribution directly. Synthesis of silica nanoparticles having narrow size distributions is not trivial, as there are many parameters affecting the characteristics of the synthesized particles. In this study, silica nanoparticles were synthesized by emulsion polymerization, where ethanol, ammonium hydroxide, and tetraethyl orthosilicate (TEOS) were mixed at room temperature. First, silica nanoparticles were synthesized in a smaller scale with a total reaction volume of 175 mL. Then the effect of various reaction parameters on the particle size distribution (PSD) was systematically investigated using asymmetrical flow FFF (AF4), a member of FFF family. The synthesis scale was then increased to the total reaction volume of 3 L. It was observed that, as the concentrations of TEOS and ethanol increased, the size of the silica nanoparticles tended to decrease, while as the concentration of ammonium hydroxide increased, the size tended to increase. Silica nanoparticles of about 100 nm having a relatively narrow size distribution could be obtained in a large scale with the concentrations of TEOS, ethanol, and ammonia solution of 95, 95, and 15%, respectively. The results suggest that AF4 is a useful tool for fast and accurate size monitoring of silica nanoparticles.