What is zeta-potential?

• A. Indicates the magnitude of interfacial charge on particle surfaces.
• B. Measures viscosity of the suspension.
• C. Can be used to control flocculation (reduces charge).
• D. Determines the color of the suspension.

Answer: (C)

Zeta-potential is the electric potential at the slipping plane within the electrical double layer surrounding a particle in suspension. It reflects the magnitude (and sign) of the interfacial charge on particle surfaces that drives electrostatic repulsion between particles. This repulsion is what helps keep suspensions stable. When the absolute value of zeta potential is large, particles repel each other and the suspension resists flocculation. If the zeta potential is reduced toward zero, those repulsive forces weaken, allowing van der Waals attractions to dominate and the particles to aggregate or flocculate. So, zeta potential can be used to control flocculation by adjusting the surface charge in the system. The other options don’t fit because zeta potential is not a measure of viscosity or color.