Emulsifiers vs Solubilisers; How are They Different?

February 5, 2021

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.

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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