Structure-Directing Effect on Silica Nanoparticle Growth in Sodium Silicate Solutions through Small-Angle X-ray Scattering

Understanding the effect of the microstructure of a sodiumsilicatesolution on the growth behavior of silica nanoparticles is necessaryfor the preparation of functional silica. The structural evolutionof silica aggregates in sodium silicate solutions was studied by small-angleX-ray scattering (SAXS) and transmission electron microscopy (TEM).The sodium silicate solution mainly contained three types of particles:monomers with a radius of gyration (R (g)) of <0.6 nm, SiO2 clusters formed by monomer polymerization,and large colloidal particles. Notably, primary particles with differentstructures in sodium silicate solutions exhibited a structure-directingeffect for silica nanoparticles formation. Assembly growth occursthrough the continuous addition of primary particles to the surface.For SiO2/Na2O < 4.2, the primary particlesare ellipsoidal, and there are more hydroxyl groups grafted on bothends of the ellipsoid, so the condensation reaction is more likelyto occur at both ends, eventually the ellipsoidal aggregates are formed.For SiO2/Na2O > 4.2, condensation reactionsoccur at equal rates in all directions, resulting in the formationof spheroid aggregates. Additionally, for SiO2/Na2O > 4.2, the primary particles maintain the fractal structureandare not easily destroyed during the carbonization reaction, so theaggregates formed by primary particles have relatively denser fractalstructure than SiO2/Na2O < 4.2. Moreover,an understanding of the sodium silicate structure and different structuralregulation mechanisms for silica nanoparticles synthesis providedan important theoretical foundation for fabricating high-performancesilica.

Automated summary

The effect of the microstructure of a sodium silicate solution on the growth behavior of silica nanoparticles was investigated. The solution contained three types of particles: monomers, SiO2 clusters, and large colloidal particles. The primary particles in the sodium silicate solution exhibited a structure-directing effect on the formation of silica nanoparticles. The understanding of the sodium silicate structure and its regulation mechanisms provided a theoretical foundation for fabricating high-performance silica.