Emulsifiers are those substances which have the function to keep water and oils bound together in a lotion; this is possible because the emulsifier has a double affinity (it is both hydrophilic and lipophilic) and therefore the two, otherwise, immiscible liquids stay together.
This double affinity however is not the same for all the emulsifiers: so to say, some emulsifiers are more hydrophilic and others are more lipophilic. The value of this proportion is called HLB (“hydrophilic-lipophilic balance”).
[If you wish to skip the more technical part… just skip it 😀 bit more down I will make things very simple 😀 for the others of you, however, who wish to learn things little bit more in detail… well, keep reading 😀 ]
The HLB value goes from 0 to 20 and it is a numerical representative of the hydrophilic and lipophilic tendencies of the material.
I have found many schemes to sum up the different properties of an emulsifier according to its HLB but, to be very honest, they were so different from each other and mostly confusing therefore I have decided to sum them up in what seems to be the common basic idea:
if the HLB is between 0-3 then it is considered more a thickening agent than an emulsifier and it is strongly lipophilic.
If the HLB is between 3-6 this emulsifier is lipophilic and will be good if you want to make a W/O (don’t freak out and keep reading 😀 ).
If the HLB is between 8-16 this emulsifier is more hydrophilic and will be good for an O/W .
What do W/O and O/W mean?
The emulsions which result from combining oils and water can be of different kinds: for example an O/W (read “oil in water”) emulsion can form, where the oil is the dispersed phase while the water is the dispersion medium; or a W/O (read “water in oil”) emulsion can form, where the water, this time, is dispersed in the oil (there are also other possible emulsions like W/O/W or O/W/O but in case I will make another post in the future).
[The most common type of emulsion however is the oil in water]
So generally emulsifiers are more hydrophilic or lipophilic and in our cream (an O/W cream), to have a very stable emulsion, we should use two emulsifiers: one hydrophilic (the most important, therefore in higher percentage) and one lipophilic (or a lipophilic co-emulsifier).
Bear in mind, however, that some emulsifiers are sold as “self-emulsifiers” which means that they are already made of two kinds of emulsifiers and therefore you don’t need to add, for example, the lipophilic.
Here I post a list of common emulsifiers and their HLB value:
3.5-4.0 glyceryl stearate W/O
4.0 lecithin (the one you can find in the supermarket)
4.7 cetearyl alcohol W/O (good lipophilic emulsifier)
5.0 cetyl alcohol W/O (good lipophilic emulsifier)
5.8 Glyceryl stearate
6.5 Polyglyceryl 3-oleate intermediate properties (not a good emulsifier)
9.7 lecithin emulsifier O/W (this is the kind of “modified” lecithin which you can buy on the websites which sell raw material)
10.0 Montanov 68 O/W (this is the commercial name of a self-emulsifier which already contains hydrophilic and lipophilic emulsifiers)
10.0 abil care 85 O/W
11.0 cetearyl glucoside O/W
11.5 Polyglyceryl-3 methylglucose distearate
12.0 methylglucose sesquistearate O/W (very good emulsifier, this is one of those which I use the most)
13.0 PEG 40 Hydrogenated castor oil emulsifier O/W and solubilizer
15.0 Polyglyceryl 10-laurate emulsifier O/W and solubilizer
16.7 Polysorbate 20 emulsifier O/W and solubilizer
This HLB value told us something about how the emulsifier is going to behave with our water and oils but there are many more important things which we still cannot know through it:
– how to use the emulsifier (does it need to be heated or does it have to be used at normal temperature?)
– at which percentage to use it (with a same HLB value different emulsifiers can be more or less strong)
[to be continued… 😀 ]