Growth kinetics and structure of a colloidal silica-based network: in situ RheoSAXS investigations

Abstract

Silica gels have a multitude of applications ranging from cosmetics and food science to oil and gas recovery. For proper design and application, it is important to have a thorough understanding of the underlying mechanisms of gel formation under different circumstances. The growth and structure of colloidal silica gels has been investigated using RheoSAXS to study the effect of silica concentration, NaCl concentration, temperature and shear rate. Additionally, SAXS in combination with a strong magnetic field has been applied to investigate the effect of magnetic microparticles and magnetic field on the development of the gel structure. Results indicate that the strongest effect on the gel kinetics are achieved by altering the activator concentration, here in the form of NaCl, followed by silica concentration and temperature. Small structural effects were also observed, with larger cluster sizes being produced at lower silica concentration and at higher NaCl concentration. Applying shear caused major changes both in structure as well as the macroscopic behavior of the silica, preventing the gel from reaching an arrested state, instead forming a viscous liquid. Applying a magnetic field appears to suppress the formation of larger clusters. The same effect is observed for increasing magnetic microparticle concentrations.