Structured surfactants, or lamellar liquid crystal-based systems, are becoming very popular to formulate shampoos and body washes that have unique properties and consumer benefits.
Structured surfactants are formed by combining specific types of anionic, amphoteric and nonionic surfactants in the right ratios in order to provide the correct geometry or critical packing parameter. This enables the formation of liquid crystal lamellar phases containing a close-packed network of spheres or multilamellar vesicles. These so-called spherulites have onion-like bilayer structures with water bound between the layers.
This structure is very different from the micelles that exist in conventional cleansers (1). Lamellar or bilayer packing is favored by using surfactants that have branched alkyl chains or by blending anionic surfactants that have large head groups/small tails with nonionics, or amphoterics that have small head groups/large tails (2). By modifying the salt content, pH, and using high shear mixing, the sheets can be forced into spheres.
Many types of surfactants form liquid crystalline phases at high concentrations however only by carefully combining the right surfactants at the proper amounts can this phase occur at more dilute concentrations.
Characterizing structured surfactant formulations
- Ability to easily emulsify oils with low shear mixing; the typical particle size of the emulsion is 1-5 microns.
- Have excellent phase stability at 45-50°.
- Rheology: high zero shear viscosity/yield point and shear thinning behavior.
- Polarized light microscopy: lamellar phases are birefringent and give characteristic patterns when viewed using polarized light.
- Single Angle X-Ray Scattering (SAXS): lamellar phases can be determined by characteristic d-line spacing 1:2:3:4 and a broad peak at 4.5A.
- Electron microscopy can visualize the multilamellar vesicle structures.
Typically used surfactants (with or without electrolyte)
Anionic
- Sodium Trideceth Sulfate
- Sodium Laureth Sulfate
- Sodium Lauryl Sulfate
- Sodium Lauroyl Glycinate
- Sodium Lauroyl Isethionate
- Sodium Lauroyl Methyl Isethionate
- Sodium Cocoyl Methyl Taurate
- Sodium Lauroyl Lactylate
- Laureth 1 Phosphate
- Diethylhexyl Sodium Sulfosuccinate
- Sodium Methyl 2-Sulfolaurate/Disodium 2-Sulfolaurate
Amphoteric
- Sodium Lauroamphoacetate
- Cocamidopropyl Betaine
Liquid crystal modifiers
- Trideceth-3
- Laureth 4
- Cocamide MEA
- Cocamide MIPA
- Glyceryl Caprylate/Caprate
- Isostearic acid
- Lauryl alcohol
Stability enhancers for improving cold temperature stability (loss of viscosity)
- Thickeners like Xanthan gum, cellulosics, and Guar Hydroxypropyl
- Trimonium Chloride
Commercially available structured surfactant blends
- Miracare SLB-365 (Water, Sodium Trideceth Sulfate, Sodium Lauroamphoacetate, Cocamide MEA-Solvay Novacare, 40-45% solids)
- Iselux SLC (Water, Sodium Lauroyl Methyl Isethionate, Sodium Lauroamphoacetate, Cocamide MIPA, Sodium Benzoate-Innospec, 44% Solids)
Structured surfactants have shear-thinning rheology with a high yield value, enabling the formulation of pourable liquids that can suspend insoluble oils, silicones, ZPT, and exfoliating beads/powders.
Yield value is the amount of force it takes to cause a product to flow — the higher the yield value, the greater the suspending power of the formulation. High yield value formulations can also create appealing visual effects like having different colored stripes or swirls in the product.
Structured surfactants can incorporate high levels of oil without sacrificing the quality and quantity of the foam or lather. The foam is rich and dense and can deliver a noticeable moisturizing feel.
For example, I have formulated foaming face washes that contain up to 80% oils that are heat stable, foam well, and have good rinse off properties. The particle size of the emulsion is remarkably small due to the extremely low surface tension of the lamellar liquid crystalline surfactant phase, even when the oil is added with low shear mixing.
When formulating with emollients, it is important to choose oils that contain over 30 carbons in order to avoid micelle formation. The formation of micelles will reduce foaming and result in lower deposition. Most vegetable oils would satisfy this criterion.
Additional benefits of using structured surfactant blends include improved mildness with less irritation versus conventional formulations, better hair shine and longer dyed hair color retention due to better emollient deposition. Typically a higher fragrance intensity/duration on skin and hair is seen versus conventional micellar based formulations.
Examples of marketed products based on structured surfactants
- Olay 2-in-1 Essential Oils Ribbons Body Wash, Jojoba Extract & Luscious Orchid
- Dove Body Wash Sensitive Skin
- Equate Deep Moisture Body Wash
- Skin So Soft Summer Soft Creamy Body Wash
Further reading
Lamellar Gel Network Technology: A Primer
References
- https://www.gcimagazine.com/business/rd/ingredients/111393889.html
- https://onlinelibrary.wiley.com/doi/full/10.1111/ics.12439
- https://www.cosmeticsandtoiletries.com/formulating/category/haircare/premium-Structured-Surfactant-Systems-for-High-Performance-Shampoos-209693241.html
Key structured surfactant patents
- Unilever: US 6150312, US 7579781, US 20030171231, US 20050137101, US 8778910
- Solvay/Novacare: EP1203063, US 9187716, US 7488707, US 20060040337, US 20150044157
- Colgate: US7737104
- Dahms: US 20070081953
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George,
Another excellent basic primer on a surfactant technology that should help formulators.
Greetings George,
Can these surfactant systems be more concentrated? I am looking for compositions which have in total less than 10 % of water (includiong all ingredients)?
Yes, it is possible to have less than 10% water.
Hello George! There is another commercial product with this technology. It is from Stepan and the blend is achieved with Sodium Ammonium Sulfate and Stepan Mild GCC. They have also patented it. I have used it and it is very easy to work with. The onions are formed with the pH adjust to around 6.0. Wishing you all the best! Regards
George, hello from Texas, would Plantaton 611L be considered a “structured” surfactant ? . If not, which one would be a good choice for hair shampoo? Thanks.
Good day!
Plantapon 611 L is a high solids surfactant blend not a structured surfactant. Iselux SLC (Innospec) is a structured surfactant mixture.
Thank you for your question,
George