The zeta potential of a colloidal suspension is a measure of the electrostatic repulsion between particles in the suspension. It is an important parameter that influences the stability of colloidal systems. The zeta potential is affected by various factors, including the pH of the suspension. When the pH of a colloidal suspension changes, it can significantly impact the zeta potential. This is because the pH affects the ionization of functional groups on the surface of the colloidal particles, which in turn influences the surface charge and the zeta potential. In general, as the pH increases, the zeta potential becomes more negative, and as the pH decreases, the zeta potential becomes more positive. This relationship is due to the ionization of acidic and basic functional groups on the particle surface.Experimental evidence supporting the effect of pH on zeta potential can be found in various studies. One such study is by Kosmulski et al. 2001 , who investigated the zeta potential of metal oxide particles such as alumina, titania, and silica as a function of pH. They found that the zeta potential of these particles changed significantly with pH, with the isoelectric point IEP occurring at different pH values for different metal oxides. The IEP is the pH at which the zeta potential is zero, and the colloidal suspension is least stable due to the lack of electrostatic repulsion between particles.Another study by Scales et al. 1997 investigated the effect of pH on the zeta potential of latex particles. They found that the zeta potential became more negative as the pH increased, and more positive as the pH decreased. This was attributed to the ionization of carboxyl and amine functional groups on the surface of the latex particles.In summary, the zeta potential of a colloidal suspension is significantly affected by changes in pH. Experimental evidence from various studies supports this observation, showing that the zeta potential becomes more negative or positive as the pH increases or decreases, respectively. This relationship between pH and zeta potential is crucial for understanding and controlling the stability of colloidal systems.References:1. Kosmulski, M., Gustafsson, J., & Rosenholm, J. B. 2001 . The pH-dependent surface charging and points of zero charge: V. Update. Journal of Colloid and Interface Science, 235 1 , 130-133.2. Scales, P. J., Grieser, F., & Healy, T. W. 1997 . Electrokinetics of the latex/aqueous electrolyte solution interface. Langmuir, 13 26 , 7064-7070.