HLB (Hydrophilic-Lipophilic Balance)
HLB (hydrophilic-lipophilic balance) is a numerical value that indicates whether a surfactant has a greater affinity for water or for oil.
Every surfactant has a part with an affinity for water and another with an affinity for grease. The HLB expresses the ratio between the two. The most widely used scale, proposed by Griffin for non-ionic surfactants, runs from 0 to 20: low values correspond to lipophilic molecules, soluble in oil, and high values to hydrophilic molecules, soluble or dispersible in water. In ethoxylated non-ionics, the HLB increases with the length of the ethylene oxide chain.
The HLB gives guidance on the function of each surfactant. Roughly speaking, low values favour water-in-oil emulsions; intermediate values, wetting and oil-in-water emulsions; and high values, detergency and solubilisation. To stabilise a particular emulsion, the aim is for the HLB of the system to match the one required by the oil phase, often by mixing two surfactants with different HLB values.
It is a formulation tool, not a measure of effectiveness. It does not take into account factors that change real-world behaviour, such as temperature (non-ionics lose solubility when heated above their cloud point), water hardness, pH or the presence of salts and solvents. For anionic and cationic surfactants Griffin's calculation does not apply and other methods are used. That is why the technical data sheets of cleaning products do not state the HLB: they describe the type of surfactant, the dose and the conditions of use.
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