Abstract: Anisotropic silica nanoparticles (AISNPs) are appealing for various applications due to their greater effective surface area and increased active sites compared to isotropic silica nanoparticles (ISNPs). Herein, we employed a sol-gel method to synthesize AISNPs utilizing the mixture of ethylenediamine (EDA) and 1,3-diaminopropane (1,3-DAP) as both structure-directing agents and catalysts. With increasing EDA:1,3-DAP molar ratio, the samples transitioned from isotropic spherical particles to anisotropic particles with increasing sizes. The synthesis of AISNP with a particle size of ca. 40 nm, average circularity (e) of 0.83, fitting ellipse aspect ratio (ar) of 1.18 and percentage of deformed particles of 83.3% was achieved with a molar ratio of EDA:1,3-DAP=7:3. It is speculated that the close proximity of EDA's amine groups facilitates their adsorption on the same primary particle through electrostatic interaction, inhibiting primary particle connections and resulting in spherical seeds that grow into small isotropic particles; the long-distance amine groups of 1,3-DAP connect adjacent particles anisotropically due to the steric hindrance, leading to large anisotropic particles; the mixtures with different EDA/1,3-DAP molar ratios result in different morphologies and sizes by their cooperative effect.

Key words: Anisotropic, Silica nanoparticle, Synthesis