A zeta potential magnitude greater than 30 mV indicates what about suspension stability?

• A. Stability
• B. Instability
• C. No effect
• D. Requires data

Answer: (A)

Zeta potential measures the electric potential at the slipping plane around each particle and reflects how strongly particles repel one another in a suspension. When the magnitude is greater than about 30 mV, the electrostatic repulsion between particles is strong enough to overcome the attractive forces that would pull them together. That repulsion keeps particles from coming close and aggregating, so the suspension remains dispersed and stable. The sign of the potential doesn’t matter here—just how large the magnitude is. It’s a useful rule of thumb, though factors like ionic strength or pH can compress the double layer and affect stability even when the measured zeta potential is high.