An emulsion basically consists of 2 liquids which are not mixable with each other. These two liquids are described as lipophilic and hydrophilic phase. The lipophilic phase is also known as the oil or fat phase (O) (even though it may not be chemically an oil). The hydrophilic phase is also called the water phase (W) (although in exceptional cases it need not be water).
In order to mix these two phases together, a further component is required, the emulsifier. There are generally two ways of combining these three components, the O/W emulsion and the W/O emulsion. In both variants, the emulsifier forms an emulsifier film and coats the droplets of the respective inner phase, which is evenly distributed in the solvent.
To determine which type of emulsion is formed by the emulsifier it is important to know the lipophilic and hydrophilic properties of the emulsifier. If the lipophilic part is predominant, the emulsifier tends to dissolve in the oil phase, which is thus defined as the external phase. In this case it is a W/O emulsifier. If the hydrophilic portion is predominant, the emulsifier will dissolve in the water phase, which forms the external phase. In this case it is an O/W emulsifier.
In the literature the term co-emulsifier or consistency enhancer is also frequently used. These are usually weak W/O emulsifiers with a strong liphophilic character such as fatty alcohols or glycerol dialkylates.
Definition: Smallest oil droplets are in the water phase. Thus the oil component forms the inner phase (or disperse phase) and the water the outer phase (or dispersant).
Properties: Water-dilutable, washable with water, forms a water rim on filter paper.
Effect: cooling, non-greasy, absorbs quickly, leaves no visible greasy shine on the skin, fast but not lasting effect.cosmetic use: E.g. as day cream, for oily to normal skin, acne etc.
Kosmetische Verwendung: Z.B. als Tagescreme, bei fettiger bis normaler Haut, Akne etc.
Typical emulsifiers: Tegomuls, Emulsan, Lame cream, Montanov™ 68, Montanov™ L, Bergamuls® ET-1.
Definition: Smallest water droplets are in the oil phase. Thus the water component forms the inner phase (or disperse phase) and the oil component forms the outer phase (or dispersant).
Properties: Oil-soluble, forms a translucent oil stain on filter paper.
Effect: Greasy, after application a visible grease film usually remains, which limits water evaporation (occlusive effect).
Cosmetic use: Mostly preferred as night cream, protective cream, sun protection products, for dry skin etc.
Typical emulsifiers: Lanolin (wool wax), wool wax alcohols, sorbitan olivate.
1. Heat the oil phase and water phase
The components of the oil phase and water phase are heated either in a water bath or in a heat-resistant glass (e.g. heat-resistant measuring cup) directly on the hotplate. The components of the oil phase must be completely melted. The temperature of the phases can be checked with a thermometer. For the different emulsifiers a slightly different temperature must be reached, which is usually between 60 °C and 85 °C. This temperature should then reach both the oil and the water phase.
2. Combining phases
As soon as the two phases have the same required temperature, the water phase is added to the oil phase in a thin stream. Now the two phases are mixed at high speed. An electric milk frother, a hand blender or an electric hand mixer can be used for this. The mixture will thicken after some time and reach a creamy consistency. This can take 1-4 minutes.
After the desired consistency has been reached and the emulsion has cooled down to hand warmth, the heat-sensitive active ingredients and preservatives can be added and stirred further. To speed up this process, the emulsion can be placed in a bowl of cold water. However, this is not necessary for small quantities and you avoid the risk of cooling the emulsion too quickly, which can affect the consistency.
3. Check and adjust pH value
Um den pH-Wert zu messen empfehlen sich pH-Indikatorenstäbchen. Diese werden mit der Emulsion bestrichen und überschüssiges Produkt kann abgestriffen werden, um die Färbung des Stäbchens zu sehen. Nach kurzer Zeit kann man die geänderte Färbung des Indikatorenstäbchens mit einem Kontroll-Farbstreifen vergleichen, um den pH-Wert abzuschätzen. Falls eine Korrektur des pH-Wertes notwenig ist kann dieser mit tröpfchenweiser Zugabe von Milchsäure (falls der pW-Wert zu hoch ist) oder x (falls der p-Wert zu niedrig ist) angepasst werden.
Finally, the emulsion should be stirred slowly by hand in order to remove the air underneath. The emulsion should at best contain no more air bubbles at the end.
Tip 1: Usually not all air bubbles in the cream are removed. Therefore, after a few days you can stir again and remove the remaining air.
Tip 2: If the emulsion should break after some time (become watery), you can simply mix the emulsion again at a touch and the consistency should thicken.