The electrokinetic potential, also known as zeta potential, of a colloidal system is a measure of the stability of the system and the degree of repulsion between similarly charged particles. In the case of silica nanoparticles in aqueous solution, the pH of the solution plays a significant role in determining the electrokinetic potential.Silica nanoparticles have silanol groups Si-OH on their surface, which can ionize depending on the pH of the solution. At low pH, the silanol groups are protonated Si-OH2+ , giving the nanoparticles a positive charge. At high pH, the silanol groups are deprotonated Si-O- , giving the nanoparticles a negative charge. The point at which the overall charge on the nanoparticles is zero is called the isoelectric point IEP .The effect of pH on the electrokinetic potential of a colloidal system consisting of silica nanoparticles in aqueous solution can be summarized as follows:1. At low pH acidic conditions , the silica nanoparticles have a positive charge due to protonation of silanol groups. The electrokinetic potential is positive, and the colloidal system is stabilized by electrostatic repulsion between the positively charged particles.2. At the isoelectric point IEP , the overall charge on the silica nanoparticles is zero, and the electrokinetic potential is also zero. At this point, the colloidal system is least stable, and the particles are more likely to aggregate due to the absence of repulsive forces.3. At high pH alkaline conditions , the silica nanoparticles have a negative charge due to deprotonation of silanol groups. The electrokinetic potential is negative, and the colloidal system is stabilized by electrostatic repulsion between the negatively charged particles.In summary, the pH of the aqueous solution has a significant effect on the electrokinetic potential of a colloidal system consisting of silica nanoparticles. By controlling the pH, one can manipulate the stability of the colloidal system and the degree of repulsion between the particles.