In the case of emulsification, it is above all the boundary interface tension on the oil-water phase boundary that must be overcome. This occurs on the one hand by the input of energy, which triggers shearing forces that reduce the size of the droplets and thus enlarge the boundary interface between the substances. On the other hand, tensides are used that have a lipophilic and a hydrophilic part and can thus mediate between the two phases.
Despite the mediation of the tensides, emulsions are unstable systems, as the fine droplets produced during emulsification merge into larger drops over time. The formation of larger drops reduces the size of the boundary interface and the emulsion breaks down. Butter, for example, is formed when cream, a milk fat-in-water emulsion, breaks down.
Applications
A classic application is the production of cosmetic emulsions for strengthening the protective acid mantle and the permeation barrier of the human skin. Other typical applications of emulsification are the preparation of
Details
The production of stable and effective emulsions presents mixing technology with a series of challenges, as not only the process parameters, such as temperature, pressure, etc. are of great importance, but also the technology employed in the field of the homogeniser. From the general geometry, the speed-dependent number of shear rates, the gap dimensions of the rotor-stator toothing and the design of feeds for other raw materials up to the housing and drive design, diverse details can cause considerable differences in quality and production speed, or decide the general feasibility of the process. Another important feature is the cleanability of the homogeniser, without dead space, in order to ensure compliance with current hygiene standards during emulsification.
If abrasive raw materials are used, such as in the case of Toothpaste, hardening of the rotor-stator teeth is also recommended, in order to increase the service life. Another large cost factor can be maintenance. Besides the rotor-stator toothing, the seal is also a particularly stressed part of the homogeniser. The seal is usually designed as a double mechanical seal. Depending on the product, the seals must be selected accordingly. We will be glad to advise you on the subject of emulsification.
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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.