Zeta Potential

Introduction

Zeta potential is a key concept in electrochemistry, colloid science, and surface science. It is a measure of the effective electrical charge of particles in a fluid, and it plays a crucial role in understanding the stability of colloidal suspensions.

Basics of Zeta Potential

Definition

The zeta potential is defined as the electrostatic potential at the shear plane of a particle suspended in a liquid. This shear plane, also known as the plane of slipping or plane of hydrodynamic shear, separates the fixed charges on the particle’s surface from the mobile charges in the surrounding liquid.

Importance

Zeta potential plays a significant role in determining the stability of colloidal suspensions. Particles with high absolute zeta potential (either positive or negative) will repel each other, preventing aggregation and leading to a stable suspension. On the other hand, if the zeta potential is close to zero, the repulsive forces between particles are weak, and the suspension is likely to coagulate or flocculate.

Measurement of Zeta Potential

Electrophoretic Mobility

Zeta potential is typically inferred from the electrophoretic mobility of the particles, which is the velocity of the particles under an applied electric field. The Smoluchowski equation relates the electrophoretic mobility () to the zeta potential ():

where is the dynamic viscosity of the fluid.

Other Techniques

While electrophoretic mobility is the most commonly used method, other techniques such as streaming potential, electroacoustic phenomena, or atomic force microscopy can also be used to estimate zeta potential.

Factors Influencing Zeta Potential

Zeta potential is influenced by several factors including the pH of the solution, the ionic strength of the solution, the nature and concentration of ions in the solution, and the properties of the particle surface.

Applications of Zeta Potential

Zeta potential is widely used in various fields, including the formulation of paints, inks, and cosmetics, the treatment of water and waste, mineral processing, ceramic processing, the pharmaceutical industry (for drug delivery systems), and in biomedical and health science research. Understanding and controlling the zeta potential can help to predict and manipulate the stability of colloidal systems.

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