The HLB value (Hydrophile-Lipophile Balance) of a surfactant is an extremely important concept that quantifies the relative strength and balance between the hydrophilic (water-loving) and lipophilic (oil-loving, hydrophobic) groups in a surfactant molecule. This numerical value is a key indicator for understanding and selecting surfactants for specific applications, such as emulsification, solubilization, wetting, detergency, and more.

Range and Meaning of HLB Values

Range: Typically 0 to 20 (some extended systems may go up to 0 to 40).

Interpretation:

Low HLB (0–6): Indicates strong lipophilicity/hydrophobicity. Such surfactants have low or no solubility in water but dissolve well in oil. They are suitable for water-in-oil (W/O) emulsifiers, defoamers, oil-soluble dispersants, etc.

Medium HLB (7–9): Exhibits moderate wetting and spreading capabilities.

Medium HLB (8–15): Provides good oil-in-water (O/W) emulsification. Higher values generally lead to more stable emulsions (for O/W types).

High HLB (13–15): Offers good detergency and cleaning performance.

High HLB (15–18): Indicates strong hydrophilicity. These surfactants dissolve well in water and are suitable for oil-in-water (O/W) emulsifiers and solubilizers.

Very high HLB (>18): Excellent water solubility, mainly used for solubilizing oily substances in water.

Methods for Calculating HLB Values

HLB values can be determined experimentally (e.g., emulsification test, cloud point method, chromatography), but calculation methods based on molecular structure are more commonly used. Below are the main approaches:

1.Griffin’s Method (for polyethylene glycol-based and polyol fatty acid ester nonionic surfactants):

Formula: `HLB = 20 * (1 - S/A)`

S: Saponification number (mg KOH required to neutralize free acids and saponify esters in 1 g of sample).

A: Acid number (mg KOH required to neutralize 1 g of fatty acid).

Limitation: Requires accurate saponification and acid values. Not applicable for surfactants with unknown or hard-to-determine saponification values (e.g., rosin esters, lanolin derivatives, polyethers).

2.Group Contribution Method (Davies Method – Broader Applicability):

This method breaks down the surfactant molecule into different groups (hydrophilic and lipophilic), each assigned a specific value (group number).

Formula: `HLB = 7 + Σ(Hydrophilic group numbers) - Σ(Lipophilic group numbers)`

Common Group Numbers:

Hydrophilic Groups:

-SO₄⁻Na⁺: 38.7

-COO⁻K⁺: 21.1

-COO⁻Na⁺: 19.1

N(tertiary amine): 9.4

-COOH: 2.1

-OH (free): 1.9

-O-: 1.3

-CH₂CH₂O- (ethylene oxide unit): 0.33 (most commonly used for polyoxyethylene ethers)

-CH₂CH₂CH₂O- (propylene oxide unit): -0.15

Lipophilic Groups:

-CH- / -CH₂- / -CH₃: -0.475

=CH-: -0.475

-CF₂- / -CF₃ ((fluorocarbon chains): ≈ -0.87 (may vary)

Benzene ring: -1.662

Benzene ring: -1.662

Calculation Steps:

1.Identify all groups in the molecule.

2.Find the group number for each hydrophilic/lipophilic group.

3.Sum all hydrophilic group numbers.

4.Sum all lipophilic group numbers.

5.Apply the formula: HLB = 7 + (ΣHydrophilic) - (ΣLipophilic).

Advantages: Broad applicability, works for both ionic and nonionic surfactants (including those unsuitable for Griffin’s method), as long as the molecular structure is known.

Disadvantages: Requires precise molecular structure; some complex groups may have uncertain or unavailable group numbers.

3.Simplified Calculation for Polyethylene Glycol Ethers and Polyether Nonionic Surfactants:

Formula: `HLB = (E / 5)`

E: Weight percentage of the polyethylene glycol (ethylene oxide, EO) chain in the surfactant molecule.

More General Formula: `HLB = (Molecular weight of hydrophilic part/Total molecular weight) * (20 / k)`

For surfactants with only polyoxyethylene as the hydrophilic group (e.g., fatty alcohol ethoxylates AEO, alkylphenol ethoxylates APEO), k = 1, simplifying to: `HLB = (Molecular weight of EO chain/Total molecular weight) * 20`

For polyol fatty acid esters (e.g., Span series), k = 5, simplifying to: `HLB = (E / 5)`，其中 `E` is the weight percentage of EO units (%EO).

Advantage: Quick and easy calculation for common polyether-based nonionic surfactants.

Practical Applications of HLB Values

HLB values are central to surfactant applications:

1.Emulsification: The most critical application of HLB.

Required HLB of the Oil Phase: Each oil or oil mixture has a specific "required HLB" for forming stable emulsions (O/W or W/O), typically determined experimentally.

Selecting Emulsifiers: Single or mixed emulsifiers are selected based on the type of emulsion of interest (O/W or W/O) and the desired HLB value of the oil phase.

O/W emulsions: Generally require higher HLB emulsifiers (8–18).

W/O emulsions: Require lower HLB emulsifiers (3–6).

Mixed Emulsifiers: Often, two or more emulsifiers with different HLB values are blended to achieve the optimal HLB for the oil phase and improve emulsification efficiency (synergistic effect). The HLB of a blend is calculated as a weighted average:

`HLB blend = (W₁ * HLB₁ + W₂ * HLB₂ + ... + Wₙ * HLBₙ) / (W₁ + W₂ + ... + Wₙ)`

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`W₁, W₂, ..., Wₙ` are the masses of each component, and `HLB₁, HLB₂, ..., HLBₙ`​are their respective HLB values.

2.Solubilization: Dissolving poorly water-soluble substances (e.g., fragrances, oils, drugs) into surfactant micelles to form clear or translucent solutions.

Requires high-HLB surfactants (>15, e.g., Tween series, Cremophor RH series) to form large enough micelles.

3.Detergency: Cleaning agents must balance wetting, emulsification, solubilization, and dispersion.

Typically requires medium-to-high HLB (13–15) for effective oil removal and dispersion in water.

4.Wetting & Spreading: Reducing the contact angle of a liquid on a solid surface to enhance wetting or spreading.

Best achieved with medium-HLB surfactants (7–9), which effectively lower surface tension and adsorb rapidly at interfaces.

5.Defoaming & Antifoaming: Breaking or preventing foam formation.

Requires low-HLB surfactants (1–3) with low solubility in the foaming medium (e.g., Span series, polyether L-series, silicone antifoams). They displace foam-stabilizing agents at the air-liquid interface, reducing film strength.

6.Dispersion: Stabilizing solid particles in a liquid medium.

HLB selection depends on the dispersion medium (water or oil) and particle surface properties.

Hydrophobic particles in water: Medium-to-high HLB.

Hydrophilic particles in oil: Low HLB.

Important Considerations

Guideline, Not Absolute Rule: HLB is a powerful screening tool but not the sole criterion. Actual performance depends on molecular structure (linear/branched), molecular weight, concentration, temperature, water quality, pH, and other additives. Final formulations must be experimentally validated.

Empirical Data: Many common oils (paraffin, vegetable oils, silicones) and surfactants have published HLB ranges for preliminary screening.

Ionic vs. Nonionic Surfactants: Griffin’s and simplified polyether methods mainly apply to nonionic surfactants. Ionic surfactants often use Davies’ method, and their HLB is more affected by ionic strength and pH.

Temperature Effects: For nonionic surfactants (especially polyoxyethylene ethers), increasing temperature reduces water solubility, effectively lowering HLB (cloud point phenomenon). This is crucial for high-temperature or temperature-sensitive applications.

Conclusion

Understanding HLB values, their calculation, and practical applications is fundamental to selecting and designing surfactant formulations. By calculating or referencing HLB values, one can quickly narrow down surfactant candidates and predict their suitability for emulsification, solubilization, wetting, or cleaning. However, HLB remains an empirical and guiding parameter—ultimate formulation performance and stability must be confirmed through rigorous testing. It is an indispensable tool in a formulator’s toolkit, but unlocking the perfect formulation also requires experience and holistic judgment.