The zeta potential value of a colloidal system is a measure of the electrostatic potential at the slipping plane, which is the boundary between the stationary layer of fluid attached to the particle surface and the bulk fluid. It plays a crucial role in determining the stability of colloidal dispersions. Changes in pH and ionic strength can significantly affect the zeta potential value, and thus the stability of the colloidal system.1. Effect of pH:The zeta potential value is highly dependent on the pH of the system, as it influences the ionization of functional groups on the particle surface. When the pH of the system is altered, the surface charge of the particles can change due to the protonation or deprotonation of these functional groups. As a result, the zeta potential value will also change.For example, if the pH is increased more alkaline , acidic functional groups on the particle surface can deprotonate, leading to a more negative surface charge and a more negative zeta potential value. Conversely, if the pH is decreased more acidic , basic functional groups on the particle surface can protonate, leading to a more positive surface charge and a more positive zeta potential value.2. Effect of ionic strength:The ionic strength of a colloidal system can also impact the zeta potential value. As the ionic strength increases, the concentration of ions in the system also increases. These ions can interact with the charged particles in the colloidal system, leading to a phenomenon called "charge screening."Charge screening occurs when counterions ions with opposite charge to the particle surface in the solution are attracted to the charged particle surface, forming an electrical double layer. As the ionic strength increases, the thickness of this double layer decreases, and the counterions are more tightly bound to the particle surface. This results in a decrease in the zeta potential value, as the effective charge at the slipping plane is reduced.In summary, changes in pH and ionic strength can significantly affect the zeta potential value of a colloidal system. The underlying mechanisms responsible for these changes are the protonation or deprotonation of functional groups on the particle surface in the case of pH changes and charge screening due to the formation of an electrical double layer in the case of ionic strength changes . These changes in zeta potential can ultimately impact the stability of the colloidal dispersion.