The zeta potential is a key indicator of the stability of colloidal suspensions in an aqueous medium. It represents the electrostatic potential at the slipping plane shear plane between the stationary fluid attached to the particle surface and the bulk fluid. The zeta potential is influenced by several factors, including pH and electrolyte concentration.1. Effect of pH:The pH of the aqueous medium has a significant effect on the zeta potential of a colloidal suspension. This is because the surface charge of the particles in the suspension is influenced by the ionization or dissociation of functional groups present on the particle surface. As the pH changes, the degree of ionization of these functional groups also changes, which in turn affects the surface charge and zeta potential.At low pH values, the surface functional groups tend to be protonated, leading to a positive surface charge and a positive zeta potential. Conversely, at high pH values, the surface functional groups tend to be deprotonated, leading to a negative surface charge and a negative zeta potential. At a specific pH value called the isoelectric point IEP , the surface charge is neutral, and the zeta potential is zero.In general, colloidal suspensions are more stable when the zeta potential is either highly positive or highly negative, as this leads to strong electrostatic repulsion between particles, preventing aggregation. When the zeta potential is close to zero, the colloidal suspension is less stable and more prone to aggregation due to the reduced electrostatic repulsion.2. Effect of electrolyte concentration:The presence of electrolytes in the aqueous medium also affects the zeta potential of colloidal suspensions. When electrolytes are added to the medium, they dissociate into their respective ions, which can interact with the charged particles in the suspension.As the electrolyte concentration increases, the ions in the solution can effectively screen or shield the surface charge of the particles, reducing the electrostatic repulsion between them. This phenomenon is known as the "double layer compression" or "charge screening" effect. As a result, the zeta potential decreases with increasing electrolyte concentration.At very high electrolyte concentrations, the zeta potential may approach zero, leading to a less stable colloidal suspension and an increased likelihood of particle aggregation due to the reduced electrostatic repulsion.In summary, both pH and electrolyte concentration play crucial roles in determining the zeta potential and stability of colloidal suspensions in an aqueous medium. By carefully controlling these parameters, it is possible to optimize the stability of colloidal systems for various applications in chemistry, materials science, and other fields.