About Colloids

Many everyday products consist of microscopic particles suspended in a fluid. These particles may be solid or liquid. We call these suspensions colloids.

Sols are solid-in-liquid colloids, and emulsions are liquid-in-liquid colloids.

Paints, inks and cosmetics – these are all colloids. Many less well-known colloids are formed during the production stages in a variety of industrial processes.

The particles in a colloid are almost always electrically charged. This charge on the particle is balanced by an opposite charge in the surrounding fluid.

The charge in the fluid is in the form of free ions. There is a region around each particle where the particle charge attracts the free ions to form an electrical cloud called the electrical double layer.

Diagram: The electrical double layer

The voltage drop across the electrical double layer is an important parameter for a colloid. This voltage drop, called the zeta potential, varies depending on the properties of the colloid.

For example, adding salt to a colloid shrinks the electrical double layer, and reduces the zeta potential.

Zeta potential and particle size are key indicators of the way colloids behave both in storage and in use. In fact, the particle zeta potential influences the effective size of the particles in the colloid, so measuring both parameters simultaneously – zeta potential and particle size itself – makes particle characterization much more reliable.

Our electroacoustic technology is the key to how we measure particle size and zeta potential.

We hold patents in applying alternating electrical fields to colloids to dynamically measure these qualities. By forcing the particles of a colloid to oscillate, we can analyze the acoustic waves they produce to quickly and accurately measure both particle size and zeta potential.