What is a dispersion?

The term dispersion is known from various scientific fields as well as from mathematics and other disciplines. In physical contexts, dispersion describes the dependency relationship between the properties of a wave and the wavelength. In chemistry, especially in colloid chemistry, as well as in process engineering, the term dispersion describes a heterogeneous mixture of at least two substances that do not or hardly dissolve in each other or combine chemically. In this process, one substance (dispersed phase, disperse phase or secondary phase) is distributed as finely as possible in another substance (dispersant, dispersive continuous phase or main phase). A mixture of gases is always homogeneous and therefore not a dispersion.

Separation / segregation of dispersions

In most cases, the individual phases in the dispersion process can also be separated from each other again by physical methods such as filtration or centrifugation. Examples of this are emulsions such as milk or aerosols such as mist. In addition, independent segregation (known as sedimentation) is possible.

Classification of disperse systems – according to particle size

Disperse systems are usually classified either by their particle size or by aggregate states. The classification by particle size comprises three levels: Particle sizes smaller than 1 nm (molecular disperse system, e.g., true solutions), particle sizes from 1 nm to 1 µm (colloidal disperse system, e.g., protein solutions), and particle sizes larger than 1 µm (coarse disperse system, e.g., milk fat globules).

Classification of disperse systems – by state of aggregation

In the classification by state of aggregation, different types of dispersions are described for two-phase dispersions depending on the states of aggregation.

Liquid

• liquid in liquid: Emulsion
• gaseous in liquid: foam
• solid in liquid: suspension

Gaseous

• liquid in gaseous: liquid aerosol (mist)
• gaseous in gaseous: gas mixture
• solid in gaseous: solid aerosol (smoke)

solid

• liquid in solid: porous solid (wet)
• gaseous into solid: porous solid (dry)
• solid in solid: solid mixture

Examples of dispersions

• solid mixture/mixture, e.g. granite
• suspension, e.g. naturally cloudy apple juice
• Aerosol, e.g. fine dust in the air
• Inclusion, e.g. wet bath sponge
• Emulsion, e.g. skin cream
• Aerosol, e.g. mist
• Porous body / solid foam, e.g. foam
• Foam, e. g. soap foam

Example Emulsion

An emulsion is a finely divided mixture of two liquids such as oil and water. One liquid (phase) is distributed in small droplets in the other liquid.

Relevance to process engineering at Ebbecke

At Ebbecke Verfahrenstechnik, dispersion plays an important role, for example in the processing of liquid products for cosmetics. Among other things, the aim is to prevent cosmetic products from separating into their individual phases again after some time. For this reason, pressure, temperature and shear sensitivity, for example, must be precisely matched to the raw material. At Ebbecke Verfahrenstechnik, processing in the mixing area usually involves high shear effects, which we can ensure by means of reactors with different mixing systems. In addition, we have special agitators for intermediate bulk containers (IBCs) and containers for stirring products with light bulk densities such as fumed silica into liquids.

In order to be able to take into account the pumpability of the individual products to be processed and to meet specific hygienic requirements, we can also choose from a wide range of special pumps when using our liquid mixing systems, including air-operated diaphragm pumps, peristaltic pumps, eccentric pumps etc.

Would you like to learn more about dispersions and the possibilities at Ebbecke Verfahrenstechnik? Just contact us or send us an email, we will be happy to advise you.