https://www.amtech.com.tw/en/custom_62115.html What is zeta potential? What is zeta potential? What is zeta potential? Zeta potential is defined as the magnitude of charge at the 'sliding surface' in the 'ion diffusion layer' around a colloidal particle.   Colloidal particle dispersed in a solution is positively or negatively charged. In order to keep the particles electrically neutral in the solution, ions with opposite polarities build up around the particles and form 'ionic stationary bed layer'.   Outside of it, there is an 'ion diffusion layer' in which ions with same and opposite polarities coexist. Since ions slide from the outside of the ionic stationary bed layer, this boundary is called 'sliding surface'.   When the zeta potential value of positively or negatively charged colloidal particles is large, the dispersion stability of the sample is good. On the other hand, when the zeta potential is close to zero, the particles have tendency to aggregate and the state of the particle system is unstable. Zeta potential provides you a guideline for the dispersion stability, aggregability, sedimentation property of small particles. Also, the charged state of surface functional group in a dispersion medium can be evaluated.