Both emulsifiers and solubilizers are part of the surfactant family and they disperse oils in water. Due to certain similarities, these terms are often confusing for formulators that are just getting started. They function differently and cannot be used interchangeably hence; it is important to understand their differences to make informed choices when selecting which to use.
What are they?
Emulsifiers are amphiphilic molecules used in formulations to facilitate the mixing of oils and water. They reduce the surface tension between two phases, keeping the oil suspended in water and vice versa. Solubilisers are very much like emulsifiers. However, the key difference is that solubilisers are completely water soluble with a little oil solubility while emulsifiers are not water soluble. Solubilsers are typically used to achieve transparent or lightly translucent solutions compared to the opaque creams that emulsifiers provide.
How are They Different?
EMULSIFIERS
|
SOLUBILISERS
| |
|
Solubility
|
Not water soluble
|
Completely water soluble with a little oil solubility |
End product appearance
|
Milky or turbid | Clear or translucent |
Particle size
| Micrometre range | Low micrometre to nanometre range |
Used for
|
Big lipophilic molecules | Small molecules like essential oils |
Working temperature
| May need heating or melting |
Usually works at room temperature |
Mechanical force
| High mechanical force needed | Low mechanical force needed |
Oil phase concentration
| 0 to 50% |
0.1 to 2% |
What is the Relationship between HLB Value and the Use of Emulsifiers and Solubilisers?
How is this value related to formulations? The Hydrophilic-Lipophilic Balance, also known as the HLB value in short, is used as a measure of the ratio of hydrophilic (water-loving) and lipophilic (fat-loving) moieties of a surfactant molecule. The HLB system is particularly useful to identify surfactants for emulsions. HLB value ranges from 0-20.
Image 2. HLB Surfactants Emulsion
How to Calculate the HLB Value?
HLB desired = (% of surfactant A) × (HLB of Surfactant A) + (% of surfactant B) × (HLB of Surfactant B)
Example:
What is the HLB value of the mixture of 40% Span-60 (HLB = 4.7) and 60% Tween60 (HLB = 14.9)?
4.7 x 0.4 + 14.9 x 0.6 = 10.8
HLB range | ||
Dispersion characteristics | No dispersability in water |
1-4
|
Poor dispersion |
3-6 | |
Milky dispersion after vigorous agitation | 6-8 | |
Stable milky dispersion | 8-10 | |
Translucent to clear dispersion |
10-13 | |
Clear solution |
13+ | |
Application | W/O emulsion |
2-6 |
Wetting agent |
7-9 | |
O/W emulsion |
8-18 | |
Detergent | 12-15 | |
Solubiliser | 15-18 |
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