Effect of Surfactants on the Formation, Morphology, and Surface Property of Synthesized SiO₂ Nanoparticles

Abstract

This study investigated the effect of cationic, anionic (saturated and unsaturated), and nonionic surfactants on the formation, morphology, and surface properties of silica nanoparticles synthesized by the ammonium‐catalyzed hydrolysis of tetraethoxysilane in alcoholic media. Results indicate that at a relatively low surfactant concentration (1 × 10⁻³–1 × 10⁻⁶ M), cationic surfactants significantly affected the growth of silica particles as measured by dynamic light scattering and transmission electron microscopic analyses. In contrast, the anionic and nonionic surfactants showed relatively minor effects in the low concentration range. The magnitude of negative zeta potential was reduced for silica colloids that were synthesized in the presence of cationic surfactant because of charge neutralization. The presence of anionic surfactants only slightly increased the negative zeta potential while the nonionic surfactant showed no obvious effects. At high surfactant concentrations (>1 × 10⁻³ M), cationic and anionic surfactants both induced colloid aggregation, while the nonionic surfactant showed no effect on particle size. Raman spectroscopic analysis suggests that molecules of cationic surfactants adsorb on silica surfaces via head groups, aided by favorable electrostatic attraction, while molecules of anionic and nonionic surfactants adsorb via their hydrophobic tails.

Keywords:

• Silica
• Surfactant
• Nanoparticle
• Colloid
• Raman spectra
• Synthesis

Acknowledgments

This research was supported by the Office of Basic Energy Sciences, US Department of Energy, under contract DE‐AC05‐00OR22725 with Oak Ridge National Laboratory, which is managed by UT‐Battelle, LLC.