Emulsion vs. Dispersion – What is the Difference?

May 6, 2014

In addition to providing sanitary pumps, valves and custom products to the high purity industries, Holland have also offers offer a line of dispersion equipment. Under various brand names, the technologies Holland offers include sanitary shear pumps, colloid mills, mixers, and high pressure homogenizers. These technologies, as the name would imply, are used for processing of emulsions and dispersions. While these terms are often used interchangeably, this post will focus on what emulsions and dispersion are and how they are different.

To begin, an emulsion can be defined as a heterogeneous system consisting of two immiscible liquid phases in which one is intimately distributed in the other as minute droplets whose diameters exceed 0.1 micrometer. In most cases, one of the liquids is water. The second liquid is usually an oil. To prevent the two unlike substances from separating out, a third liquid, known as a surfactant, is used to prevent coalescence of the dispersed liquid. Common emulsions include milk, vinaigrettes, greases, and cutting fluids for metal working.

When oil is dispersed as extremely fine droplets in a continuous phase of water, the emulsion is known as an oil-in-water emulsion. When oil is the continuous phase, it is known as a water-in-oil dispersion. The type of emulsion that is formed is greatly dependent upon the nature of the surfactant used. While emulsions can form spontaneously, provided there is enough surfactant, as a general rule of thumb, the more energy used to generate an emulsion, the less surfactant you will need. This means that a high pressure homogenizer processing an emulsion will require less surfactant than a high shear mixer.

A dispersion, or suspension, on the other hand is defined as solid primary particles, agglomerates, or aggregates distributed uniformly throughout a continuous medium. These particles can range in size from 0.001 micrometers on up to greater than 1 micrometer. A dispersion can be defined as a colloid if particles sizes is between 0.001 micrometer and 1 micrometer. Examples of dispersions include ink, dyes, ketchup, and antacid.

The dispersion formation process is can be broken down into three main components. The first step is wetting. In the wetting step, air is displaced from the particles by the continuous phase. The next step is physical separation. This is where a shear device of some sorts is used to impart a large amount of mechanical energy. The last step involves stabilization to prevent re-adhesion of particles. The stabilizer is similar to a surfactant, but some weak re-agglomeration and flocculation is sometimes desired.

The process of dispersing is sometimes called “milling” or “grinding”. In actuality, no particle grinding is actually occurring. As mentioned previously, the type of equipment used to create a dispersion or emulsion varies and is depend on the characteristics of the product and process. Ball or sand mills are often used on extremely high viscosity products. Colloid mills are used in continuous, low viscosity systems. Homogenizers can be used in all the same applications as a colloid mill, but high pressure homogenizers are most efficient at lower viscosities and are more capable at creating small particle sizes than colloid mills.

Waukesha Colloid Mill

Waukesha Colloid Mill

Ultimately, the utility of a homogenizer or piece of dispersion equipment comes from the unique changes to the product after processing. Homogenizers can defibrillate cellulose and alter the tomato fibers in ketchup to produce a thicker product and improve product texture. If you have a homogenization application, contact a Holland Sales Engineer today. We offer a variety of products including mixers, shear pumps, colloid mills, sanitary homogenizers and SPX’s unique new Cavitator technology.   We would be happy to work with you to tailor equipment to your specific process and improve your product.