What are Surfactants?
What are Surfactants?
In cosmetics and personal care products, surfactants are cleansing and foam-forming agents. They form the base of almost all cleansing products available. They mix with water and fat on the skin to remove dirt.
The term "surfactant" is broadly used to denote surface activity. It is noted for its ability to reduce the surface tension between two phases. In general, surfactants may act as:
- Detergents
- Wetting agents
- Emulsifiers
- Foaming agents, and
- Dispersants
The lipophilic chain is attracted by the soil and penetrates it, while the surfactant forces the soil to an open surface area and then detaches from the surface.
How do surfactants work?
A key to utilizing surfactant's unique properties lies in understanding how and when to use them.
Surfactants in cosmetic personal care formulas can be easily incorporated, but this requires skillful execution of surfactant-related processes. Surfactant molecules rest at a water interface, forming a thermodynamically stable system that prevents polar and non-polar solvents from contacting each other. Thermodynamically stable systems primarily include: micelles, lamellae, microemulsions, emulsions, and liquid crystals.
Polar and non-polar components of a surfactant provide varying affinity that allows a surfactant to attract to specific solvents.
- Polar component: This component is hydrophobic in nature. It is insoluble in water and can be in various forms such as:
- linear or branched,
- alkyl and aromatic,
- sulfuric, nitrogenic, phosphoric, and
- alkoxylate groups combined.
- Non-polar component: This component is hydrophilic in nature. This region determines a surfactant's classification.
- Nonionic (polyalkoxylate, glucose, sucrose, amine oxide) - No charge
- Anionic (sulfate, sulfonate, carboxylate, phosphate) - Negative charge
- Cationic (alkylammonium salts) - Positive charge
- Zwitterionic (which contains both anionic and cationic groups)
Types of Non-polar Component of a Surfactant
Role of surfactants in cosmetics
Surfactants play a crucial role in cosmetic formulations as cleansing agents. Some key roles surfactants serve in cosmetics include:
-
Emulsification - Surfactants can emulsify or blend two immiscible liquids like oils and water. This allows oil-based moisturizing ingredients to mix well with water in creams, lotions, etc.
- Foaming/Lathering - Many surfactants generate foam and lather when rubbed with water. This gives a visual cue of cleansing activity and makes the application of cleansers enjoyable.
- Deep Cleaning - The polar and nonpolar structure allows surfactants to cut through oil, and dirt and lift them off the skin or hair. This helps thoroughly clean the surface.
- Solubilization - Surfactants help solubilize essential oils and fragrances in the water phase. They disperse them evenly in products like shower gels. This provides heat and physical stability.
- Conditioning - Some surfactants act as mild conditioning agents themselves leaving a smooth softened feel to the hair or skin. Examples include betaines and fatty acid surfactants.
- Thickening & Stabilizing - Surfactants adjust the viscosity and stabilize emulsions. This is done through their oriented alignment at oil-water interfaces. This improves texture.
Knowing about the role of surfactants in cosmetics is crucial. It's important to note their behavior when they are added into the formulation.
Many options of surfactants are available in the market today. But, are you finding it difficult to select the right type for your cosmetic formulation? Let's help you make the right choice to formulate your cosmetic products.
In the section below, we will dive deep into the different classes of surfactants. The common strengths, weaknesses, and examples of each class are also mentioned.
Classification of Surfactants
Classification of Surfactants
There are many options for creating surfactancy and delivering end-user benefits. Obtaining the following properties is essential such as:
-
low/high foaming,
- non-residue/residue deposition, and
- viscosity/rheology modulation
A synergist balance is required within chemistry and classification to achieve targeted physical and sensorial properties. Most surfactants provide adequate levels of surfactancy. The table below shows the surfactant types to know what properties they impart when added to a cosmetic formulation.
Functionality Matrix of Anionic Surfactants
Anionic surfactants are incorporated for their surface activity (negative charge polar head groups like carboxylic acid, sulfates, sulfonic acids, and phosphoric acid derivatives)
Anionic Surfactants Chemistry
|
Classification & Examples
|
Benefits |
Weaknesses |
Sulfates
|
- Ether sulfates have better solubilitythan un-ethoxylated counterparts
- Sacrifice some foaming characteristics and surfactancy
|
- Can be irritating if left on the skin
|
|
Sulfo-derived
|
- Less irritating than sulfates
- work well in soft and hard water; less effective in hard water at low pH's)
- Compatible with cationics
- Higher degree of utilization due to negative emotive issues with sulfates and improving economics
- Stable in aqueous systems
- Susceptible to hydrolysis
- Leaves a dry feel to skin
- Good foaming, especially in acid pH
- Has the potential to reduce irritation values of a surfactant system
|
- Susceptible to hydrolysis
- Poor foamer
- Could cause minimal irritation and minimal damage to cuticle
|
Miscellaneous
|
Taurates
|
Anionic surfactants - Select grades from the list available in our database
|
Functionality Matrix of Cationic Surfactants
Cationic surfactants are incorporated for their electrostatic attractive properties to skin and hair, and substantivity (positive charge polar head groups like amines, alkylimidazolines, alkoxylated amines, quaternary ammonium)
| Cationic Surfactants Chemistry |
| Classification & Examples |
Benefits |
Weaknesses |
Amines
- Alkylamines
- Alkoxylated amines
- Amine Oxides
- Alkanolamides
- Amphoterics (e.g., Alkylamido alkylamines)
|
- Good for acidic systems - provide good conditioning properties
- Good foam boosters
- Stable in amphiphilics
- Reduce irritation of sulfate systems
- Foam boosters
- Improved substantive conditioning
|
- Contribute an amine odor to the formula
- Potential irritants
- Under-utilized because of poor purity in the past
|
Alkylammonium salts
- Alkyltrimethylammonium salts: cetyl trimethylammonium bromide (CTAB)
- Cetylpyridinium chloride (CPC)
- Benzalkonium chloride (BAC)
- Benzethonium chloride (BZT)
- 5-Bromo-5-nitro-1,3-dioxane
- Dimethyldioctadecyl ammonium chloride
- Cetrimonium bromide Dioctadecyldimethyl ammonium bromide
|
- Good for acidic systems- good conditioning properties.
- Good foam boosters
- Stable in amphiphilics
- Reduce irritation of sulfate systems
- Used for their foam boosting properties
- Increase viscosity
- Can be used in low pH systems
- Reduce irritation value of anionics
- Foam booster with improved substantive conditioning
|
- Have been under-utilized because of poor purity
|
Cationic Surfactants - Select grades from the list available in our database
|
Functionality Matrix of Non-ionic Surfactants
Non-ionic surfactants are incorporated as emulsifiers, conditioning agents, and solubilizers/coupling agent (no charge and represented by alkylene oxides, polyglucosides, fatty alcohols, ethanolamines, dimethylamine oxides)
| Non-ionic Surfactant Chemistry |
Classification
|
Example
|
Benefits |
Alkoxylated alcohols (Ethers)
|
Random copolymers:
|
- Produce extensive foam
- Are mild
- Leave a substrate soft and smooth to the touch
|
Esters & Glucosides
|
Glycerides:
- Sorbitan esters
- Alkyl glucoside
|
- Limited surfactancy but good conditioning properties
- Good hydrophobe
- When ethoxylated, yield very good coupling agents and mild conditioning agents
- Mild conditioning, co-emulsification, and thickening
- Good foamers, good detergency, diverse compatibility
Limitation
- Poor stability in highly acidic mediums
|
Glucose, Sucrose, Amine Oxide
|
- Cocamide MEA, Cocamide DEA
- Dodecyldimethylamine oxide
|
Non-ionic surfactants - Select grades from the list available in our database
|
Functionality Matrix of Zwitterionic Surfactants
Amphoteric surfactants are incorporated as secondary surfactants to help boost foam, improve conditioning, and reduce irritation (zwitterionic with positive and negative depending on the pH of the environment)
| Zwitterionic Surfactant Chemistry |
| Classification
|
Example
|
Amphiphilic
|
- Sodium dodecyl sulfate (anionic)
- Benzalkonium chloride (cationic), Cocamidopropyl betaine (zwitterionic)
- Phospholipids
- Sodium dodecyl sulfate (anionic)
- Benzalkonium chloride (cationic),
Cocamidopropyl betaine (zwitterionic)
- Phospholipids
- Cholesterol
- glycolipids
|
Betaines
|
- Behenamidopropyl Betaine
- Betaine
- Coco-Betaine
|
Sultaines
|
- Cocamidopropyl Hydroxysultaine
- Coco-Sultaine
|
Amphoteric surfactants - Select grades from the list available in our database
|
Now that you have selected which type of surfactant(s) to choose, let's understand how to make your selection process easy and the factors to consider while formulating cosmetic products.
Tips to Select the Right Surfactant System
Tips to Select the Right Surfactant System
The selection of the right surfactant system is difficult because of the diversity of options. When deciding upon a system:
- Consider the interaction of ingredients and how a surfactant-based cleansing system will be positioned in the marketplace
- Chose the raw material manufacturers because they might employ different processes:
- There is always a concern - as relates to manufacturer variations - regarding the quality and performance of ingredients
- There can be variances in the consistency of ingredients from batch to batch and lot-to-lot
- Surfactant specifications are critical to ensuring viscosity control, color, odor, pH, salt content, and foaming/cleansing characteristics
The general mechanism of surfactant is similar - care should be taken, understanding why a surfactant is used and how to determine the selection of the right combination of surfactants is important. Everyday functional uses of surfactants include:
- Detergency to remove soil - e.g., in shampoos and soaps
- Wetting to improve the contact angle between a solution and a substrate - e.g., in the coloring of hair and applications of permanent wave lotions
- Foaming for appearance - e.g., in shampoos, bubble bath, and laundry detergents
- Emulsification to form a stable mixture of two incompatible phases to include oil-in-water, water-in-oil, multiple phases, clear micro, alcoholic, nano-, and refractive index matching - e.g., in skin and hair creams and lotions
- Solubilization of insoluble components such that they are compatible in an incompatible system - e.g., in perfumes and flavors
Practical Aspect on Surfactant Chemistry
An important step in developing a cleansing-type product is to consider how surfactants will be incorporated into them to optimize performance and processing. The main performance properties of cleansers are:
- Quality of the foam
- Structure and amount (e.g., creamy, loose, tight, quick breaking, etc.), and
- Cleansing action
Physical compatibility of surfactant components can depend on viscosity, phase separation of liquids, crystallization, solubility limits, and temperature changes.
Important Considerations While Formulating with Surfactants
- Choosing the right surfactant type/co-surfactant system which has the greatest solubility for the oil phase.
- Adjusting the ratio of surfactant to co-surfactant.
- Determining the ratio of oil to surfactant/co-surfactant mixture.
- Add sufficient water to find the right microemulsion region.
Fundamentals to Successful Cleanser Construction
Fundamentals to Successful Cleanser Construction
While formulating any cleansing product, there are key considerations, as listed below, which you should be aware of and evaluate beforehand.
- Determination of which part of the body is to be cleansed
- Foam size and structure
- Ease of building foam
- Feel during application and after rinse-off
- Viscosity during dispensing and use; and
- Deposition of active ingredients
| Surfactant Type |
Foam Structure |
Foam Break |
Deposition |
Skin Feel |
Viscosity |
Mildness
|
| Anionic |
⭐ ⭐ ⭐ |
⭐ ⭐ ⭐ ⭐ |
⭐ ⭐ |
⭐ ⭐ ⭐ ⭐ |
⭐ ⭐ ⭐ |
⭐ ⭐ ⭐ |
| Ether Sulfates |
| Sulfonates |
| Sulfosuccinates |
| Isethionates |
| Ammonium Halide Quats |
|
Preferred Applications: Effective cleansing;
Shampoos;
Hand cleansers;
Mild cleansing;
Sensitive cleansing formulations
|
Cationic
|
⭐ ⭐ ⭐ ⭐ |
⭐ ⭐ |
⭐ ⭐ ⭐ ⭐ ⭐ |
⭐ ⭐ ⭐ ⭐ ⭐ |
⭐ ⭐ ⭐ ⭐ ⭐ |
⭐ ⭐ ⭐ ⭐ ⭐ |
| Amines |
| Alkanolamides |
|
Preferred Applications: Hair Conditioning; formulations for damaged hair |
Non-ionic
|
⭐ ⭐ |
⭐ ⭐ ⭐ ⭐ ⭐ |
⭐ ⭐ |
⭐ ⭐ |
⭐ |
⭐ ⭐ |
| Alkoxylated Alcohols |
| Amine Oxides |
| Carbohydrates |
|
Preferred Applications: Mild cleansing; pH-independent formulations |
Zwitterionic
|
⭐ ⭐ ⭐ ⭐ ⭐ |
⭐ ⭐ |
⭐ ⭐ ⭐ ⭐ ⭐ |
⭐ ⭐ ⭐ ⭐ |
⭐ ⭐ ⭐ ⭐ ⭐ |
⭐ ⭐ ⭐ |
|
Preferred Applications: Mild cleansing formulations; Baby Shampoos |
Performance Matrix - Cleansers for Face, Hand, and Body Care
It does not stop there. Also necessary is the development of an aesthetically pleasing product that consumers will continue to use. Additionally, as in-process foaming is a concern, consideration of equipment used during formulation is of importance; and, as surfactants need to dissolve quickly and fully, equipment, the order of addition of ingredients (to include surfactants), mixing rate, and temperature need to be considered.
Selection of a surfactant system is difficult because of the diversity of options. When deciding upon a system, it is important to consider the interaction of ingredients and how a surfactant-based cleansing system will be positioned in the marketplace. Because no two raw-material manufacturers use the same process(es), there is always a concern – as relates to manufacturer variations – regarding the quality and performance of ingredients.
Additionally, with any given manufacturer, there can be variances in the consistency of ingredients from batch to batch and lot to lot. Thus, surfactant specifications are critical to ensuring viscosity control, color, odor, pH, salt content, and foaming/cleansing characteristics.
When constructing a cleansing formula, one needs to divide the formula into functional buckets:
- Water
- Primary Surfactant(s) - The workhorse ingredient(s) required to remove soil from a substrate
- Co-Surfactant(s) - Used to add structure to formula (and could add foam density); conducive to forming a micelle structure that confers higher viscosity (Alkanolamide MEA and Betaines being the more common options)
- Rheology Modifier(s) - There are two types of rheology modifiers: polymeric and high melting point wax. Polymeric thickeners include Acrylate-chemistry, cellulosic, and gums (guar, xanthan and locust). High molecular weight/melting point waxes (e.g., Stearyl Alcohol and PEG esters) produce crystalline structures that provide a suspension of insoluble components. Their performance properties include:
- Controlling rheology and yield stress - modifying the appearance, flow, and texture to alter pour and at-rest characteristics
- Stabilizing oils and suspended particles
- Thickening of surfactants - i.e., those that do not thicken with the addition of salt
- Aesthetic modification - e.g., to impart a modified feel during application
- Viscosity stabilization - i.e., preventing viscosity drift during long-term high-temperature stability testing
- Preservative(s) - Since cleansing product tend to be based on aqueous systems at relatively neutral pH, preservatives are critical to maintaining a micro-organism-free system
- pH Adjuster(s) - Alkaline and/or acidic (e.g., sodium hydroxide and citric acid)
- Miscellaneous Functional Ingredients -
Face Cleanser Formulations
Hair Cleanser Formulations