Improved Surface Coating Methods of Silane Coupling Agents on Silica Nanoparticles to Enhance Stability and Surface Coverage

Open Access
Reilly, Daniel Timothy
Area of Honors:
Chemical Engineering
Bachelor of Science
Document Type:
Thesis Supervisors:
  • Themis Matsoukas, Thesis Supervisor
  • Wayne Roger Curtis, Honors Advisor
  • Darrell Velegol, Faculty Reader
  • Colloid Stability
  • Heat Transfer Fluids
  • Silica
  • Nanoparticles
The surface of silica colloidal particles in aqueous solution was modified with three silane coupline agents: 3-aminopropyltriethoxysilane (APES), aminopropyldimethylethoxysilane (APMS), and N-[3-(trimethoxysilyl)propyl]ethylenediamine (TMPE). Two methods for the addition of the SCAs were employed. Either direct addition of pure SCA or dropwise addition of the SCA diluted to low concentrations in ethanol. In addition, the effect of timing of SCA addition was investigated by adding dilute SCA either quickly over 15-20 minutes or prolonged in stages over several days. The stability of the particles was measured with dynamic light scattering (DLS) and zeta potential measurements. In addition, the percentage of surface of the particles that had been covered with SCA was determined both qualitatively by comparing zeta potential profiles of samples with varying amounts of SCA added, and quantitatively by comparing the amount of SCA that had been added to a theoretically calculated maximum value for complete coverage. In the direct addition of SCA, untreated silica showed the greatest stability at neutral pH as measured by DLS. The lowered stability when SCA is added is hypothesized to be caused by low surface coverage causing an overall decrease in the magnitude of zeta potential. The dilute addition of SCA in ethanol allows for much higher amounts of SCA to be added than in direct addition, resulting in much higher levels of surface coverage. The higher amount of surface coverage is confirmed by measuring zeta potential over a pH range for increasing amounts of SCA added, and TMPE allowed for the highest amount of addition compared with APES and APMS. TMPE dilute addition was also tested over a longer addition time of several days which resulted in higher coverage and the most stable treated particle dispersions achieved so far.