An emulsion is a fine mixture of two immiscible liquids, as in a cream. Emulsification combines these phases into a stable system. The goal is to break up the inner phase into fine droplets and so enlarge the interface between the two liquids.
How emulsions stay stable
Emulsions are usually cloudy and milky. How long they last depends, among other things, on temperature and pH. During emulsification, the interfacial tension between oil and water must be overcome. There are two ways to do this:
Adding energy
Shear forces reduce the droplet size and enlarge the interface between the substances.
Surfactants and emulsifiers
They have a lipophilic and a hydrophilic part and so mediate between the phases. They also prevent droplets from merging again.
Nevertheless, emulsions remain unstable systems. Over time, fine droplets merge into larger ones until the emulsion breaks. Butter, for example, forms when cream, a fat-in-water emulsion, breaks. Finer droplets have less buoyancy and slow down creaming. In addition, substances can help that increase viscosity, make the droplets repel each other electrically or act as surface-active agents in other ways.
Applications
A classic example is cosmetic emulsions that strengthen the acid mantle and barrier of the skin. Other typical applications:
What matters in emulsification
Besides process parameters such as temperature and pressure, the homogeniser technology determines quality, production speed and even feasibility. Key points are:
- Geometry and speed-dependent shear rates
- Gap width of the rotor-stator teeth
- Design of the feeds for further raw materials
- Housing and drive
- Cleanability and absence of dead spaces for current hygiene standards
- Hardened teeth for abrasive raw materials, for example in toothpaste
- A low-maintenance seal, usually a double-acting mechanical seal with suitable material
Related processes are homogenisation and dispersion. We also advise on and sell used homogenising mixers and process plants.
Our latest innovation is the dosing station for efficient weighing and dosing of liquid raw materials.
Other processes
Frequently Asked Questions about emulsification
What is an emulsion?
A fine mixture of two immiscible liquids, such as oil and water, which is stably combined by emulsification – as in creams and lotions.
How does an emulsion become stable?
Through energy input that breaks up the droplets and emulsifiers or surfactants that mediate between the oil and water phases. Thickeners can also slow creaming. Temperature and pH also play a role.
Why does an emulsion break?
Fine droplets merge into larger drops over time (coalescence). This reduces the interface and the phases separate – this is how butter forms from cream.
What matters in a homogenizer for emulsions?
Geometry, shear rates and gap of the rotor-stator toothing, feeding of further raw materials, drive design, cleanability and freedom from dead space – and for abrasive products such as toothpaste, hardened toothing and suitable mechanical seals.