Introduction to Emulsifiers
Introduction to Emulsifiers
Emulsifiers are ingredients used in cosmetics to help mix substances that usually don't blend well like oils and water. Emulsifiers work by reducing the tension between liquids that don't dissolve in each other. They allow the liquids to mix together and stay mixed, rather than separate.
How do emulsifiers stabilize mixtures?
Emulsions are systems composed of two or more immiscible materials. Here, one material suspends or disperses throughout another material in separate droplets. The immiscible phases can be water, oil, or silicone.
While making emulsions, surfactants called emulsifiers slower the separation of the immiscible phases. All emulsions are unstable with the exception of some spontaneously forming microemulsions.
Simply put, any combination of unlike phases that are put together can be considered a type of emulsion. Emulsions are classified by:
- The continuous phase (external)
- The discontinuous phase (internal)
The use of homogenizers and other equipment to minimize droplet size will improve the stability of an emulsion.
Emulsifiers Slower the Separation of the Immiscible Phases
When naming the emulsion type, the first letter is the discontinuous phase.
- O/W stands for oil-in-water and is classified as an emulsion.
- W/O stands for water-in-oil and is classified as an invert emulsion.
- These types of emulsions are much more difficult to stabilize than oil-in-water systems.
- They also must have much smaller droplets to help them stay together longer.
Making emulsions can sometimes be fun, and sometimes not. When things go well, it certainly is a lot of fun. In all cases, emulsions vary in the size and type of each of the phases. This phase ratio is critical in determining the characteristics and performance of the resulting product.
Changing the phase ratio alters the physical properties of the emulsion. It is the emulsifiers that help keep emulsions together.
Why is the stability of emulsions important?
It is clear that emulsions are dispersed multiple phase systems. They are made out of at least two nearly immiscible fluids; one being dispersed in the other. The dispersed phase forms droplets, which are surrounded by the continuous phase. Multiple emulsions are very complex systems.
Compared with simple emulsions consisting of only two phases, much more destabilization processes need to be taken into consideration for complex emulsions. In cosmetics and personal care products, complex emulsions are useful to prepare:
- sustained release aerosol fragrances,
- prolonged skin moisturizers and protection of sensitive biologicals,
- personal care formulations for perfumes, skin lipids, vitamins, and free radical scavengers and much more.
Thus, guaranteeing long-term stability of cosmetic emulsions is necessary. But it can be difficult & costly. As many factors trigger instability, you may lose too much time finding the right causes & appropriate solutions.
What are the benefits & limitations of emulsifiers?
Emulsifiers provide several important benefits to end consumers in cosmetic products:
- Improved product texture: Imparts smoothness and creaminess in lotions and creams.
- Sensory appeal: provide a non-greasy, velvety after-feel on the skin.
- Effective and even application: Improve the spreadability of products on the skin.
- Absorption: They enhance quick absorption of certain ingredients into the skin or hair.
- Foaming properties: Produces good foam boosting contributing to the lathering of shampoos and body washes.
- Natural and organic appeal: Certain emulsifiers can be derived from natural resources. They can also have a vegetal or biobased origin.
- Multifunctional benefits: Show moisturizing, thickening, and non-irritant properties on the skin.
Creating cosmetics could be a task without having knowledge about the ingredients involved. Before adding any ingredient, it becomes necessary for you to know about the strengths and weaknesses it imparts.
Considering these aspects beforehand, will help you decide if the additive is required or not. If added, would it give an extra edge to the end product? Also, it could help you engineer the formulation to achieve desired end-use requirements.
Similarly, it is wise to look upon the features to stumble upon the right emulsifier. The table below discusses the benefits and limitations associated with emulsifiers.
|
Benefits |
Limitations |
| Correct use of emulsifiers creates homogenous mixtures, dispersions or emulsions of oily or waxy substances with water. |
Being physically unstable they get separated into distinctive phases. |
| Addition of emulsifiers helps solids to be dispersed in liquids or insoluble liquids with other liquids. |
The dispersed oil droplets can fuse together and rise in o/w emulsion or may get settled down in w/o emulsions. |
| Greasy anhydrous creams can be modified to washable ones. |
Permanently irreversible separation and fusion of the dispersed phase may occur. Conversion of w/o to o/w (or vice versa) can be observed. |
Now that we've covered the basics of emulsifiers and their importance in cosmetics. Let's dive deeper into the various categories and types available.
Classification of Emulsifiers
Classification of Emulsifiers
Emulsifiers can be classified into different categories based on various criteria:
Ionic nature - Based on ingredient's chemistry
Anionic emulsifiers
Anionic emulsifiers are, in some ways, the old-fashioned cousins when it comes to emulsifier technology. Soap-based emulsifiers can be extremely useful in cleansing formulations. But they can also form part of a very elegant high-end anti-aging formulation as long as your selection of actives is carefully chosen.
- Anionic emulsifiers carry a net negative charge in solution. Thus, they are sensitive to electrolytes like cations.
- Anionics benefit from the presence of a little monovalent salt or acid up to a point. It increases the saltiness/acidity up to critical micelle concentration and activity of the water phase).
Above that, the formula can critically fail in a similar way like over-salted surfactant blends. Salt content can creep up in an active formula containing ingredients such as:
- Aloe
- Sodium PCA
- Seaweed Extracts
- Sodium Hyaluronate, and
- even some herbal actives can push the limits
As such, freeze/thaw stability is an essential part of early anionic emulsion stability testing
The old pharmacopeia-driven Sodium Lauryl Sulfate has been replaced. This is because of its ‘harsh-on-skin’ reputation. Anionics, especially elegant phosphate esters are known for their skin compatibility. Gentle surfactants such as lactylates or glutamates make it possible to make an anionic emulsion that is kind and gentle on the skin. Anionic emulsifiers are the most commonly used in emulsions. For example, Sodium Laureth Sulfate.
The PEG-100 part of the emulsifier is a function of adding Polyethylene Glycol, or PEG. This process is called ethoxylation which is a common attribute of anionic emulsifiers. They are also compounds that have been ethoxylated. This process creates ingredients that have varied amounts of water solubility.
The higher the amount of ethylene oxide (EtO), the more water solubility the emulsifier has
The one major issue with ethoxylates is that they can be irritating at high levels. The molecular formula for
Polyethylene Glycol is given below, where "n" is the number of moles of ethylene oxide
in the molecule.
OH–(CH2–CH2–O)n–H
Structure of Polyethylene Glycol
Cationic emulsifiers
Cationic technology for skin care arose from the wool industry. It then transferred to hair care. Hair care and skin care are both keratin-derived. Hence, it didn’t take long for the benefits of cationics to harness. These advantages took place in moisturizer technology.
Cationic emulsifiers function very well in formulations that are desired to stay on the skin for a long time such as:
-
sunscreens,
- long-wear make-up, and
- barrier creams
This is because, they have a positive charge. The cationic charge adheres these products strongly to the surface of the skin. This thereby resists wash-off and wear. An example of cationic emulsifiers is in preventing sand from sticking to a freshly-sun-screened body. Thanks to its anti-static capacity.
Like anionics, cationics are also sensitive to what is going on in the water phase. They can cope best with a relatively quiet external phase rather than one loaded with additives. Due to their natural capacity for skin adhesion, they can be more likely to irritate than other chemical families. Having said that, in many cases, the formulator can work around this – formulating to an acidic pH is advisable.
The new generation of cationic emulsifiers tends to favor long hydrophobic tail(s). These tails have the effect of reducing the charge density of the head group. This thus minimizes the irritation potential. This, of course, must be balanced by the ingredients' capacity to form and hold an emulsion.
As with anionic emulsifiers, cationics do benefit from a little monovalent salt. This can boost the CMC and as a consequence, the viscosity. But beyond a certain point, the salt becomes detrimental to stability.
Note: While using a cationic emulsifier system the formulator does rule out the use of pretty much all grades of Carbomer, and even anionic thickening agents such as xanthan, unmodified guar and tragacanth.
|
Cationic emulsifiers are those that are mostly used in hair care products. These are commonly called quaternium ammonium compounds or "quats". An example is Distearyldimonium Chloride.
- Apart from having excellent emulsification capabilities, they act as hair conditioners. This is because of their natural electrical charge in association with that of the hair.
- They also have very good preservative activity such as Quaternium-15 (Hexamethylenetetramine Chloroallyl Chloride or Dowicil™ 200). These ingredients are very substantive and quite functional.
One disadvantage of cationics is that they can be somewhat irritating at high levels. The irritancy is more so than the anionic emulsifiers with higher levels of ethoxylation.
Cationic emulsifiers exhibit a charge on the molecule with the use of a halogen ion, such as a chloride or bromide. Below is an example of Quaternium-70 (Stearamidopropyl Dimethyl Myristyl Acetate Ammonium Chloride). An ingredient that can act as a cationic emulsifier and anti-static conditioning agent in hair care.
Structure of Quaternium-70
Notice the ammonium groups [-NH-] and the chloride ion, which gives the molecule its negative charge.
Non-ionic emulsifiers
Non-ionics emulsifiers remain the first choice go-to emulsifiers for most applications. This is due to their flexibility and low potential for chemical interaction. Non-ionic emulsifiers are those that are free from any external electrical charge caused by free ions.
Examples of these are:
- Polysorbate 80
- Polysorbate 20
These are familiarly known as Tweens™, a common trade name for emulsifiers offered by Croda.
It is often a non-ionic emulsifier blend that is chosen first when creating creams with high activity levels or hard-to-stabilize ingredients such as:
- Salicylic acid
- AHA’s
- Zinc Oxide or high strength vitamin C
There were ingredients such as Seppic’s MONTANOV™ 68 MB that first got us hooked on the self-emulsifying blend of non-ionic and freed us from the trials of calculating HLB in a complex oil-phase world.
The key benefit of a non-ionic emulsifier is its robust salt tolerance.
In fact, the addition of a little non-ionic is recommended in ionic emulsions as the mixed micelles that will form tend to display a dramatically enhanced salt tolerance over the ionic alone.
While the presence of self-emulsifying blends has made things easier, it doesn’t for a moment mean we shouldn’t consider what is going on inside of our product.
The HLB system is alive and well in the non-ionic world and gives us a great insight into where the emulsifier will orient itself and whether it is able to bring any other features to the product. That said, it is also important to mention the existence of more than one HLB system so that one can compare like with like.
Amphoteric emulsifiers
Amphoteric emulsifiers are emulsifiers that can exhibit both anionic and cationic properties. This depends on the pH of the surrounding environment.
Some key characteristics of amphoteric emulsifiers include:
- At a specific pH point, known as the isoelectric point, they carry no net charge.
- Betaines, sulfobetaines, and certain amino acid derivatives are common examples of amphoteric emulsifiers.
- Generally mild and low irritating makes them suitable for sensitive skin or baby care.
- Can be used to stabilize both oil-in-water (O/W) and water-in-oil (W/O) emulsions.
- Exhibit good foaming and cleansing properties making them useful in shampoos and body washes.
- Compatible with a wide range of ingredients, including anionic, cationic, and non-ionic surfactants.
Amphoteric emulsifiers are not as widely used as anionic and non-ionic emulsifiers. They offer mildness, low irritation, and compatibility with different pH conditions.
Discover the complete range of emulsifiers based on their ionic nature available in our database.
Chemical composition
Fatty acid-based emulsifiers
Fatty acid-based emulsifiers are a class of emulsifiers derived from fatty acids. They consist of a long, non-polar hydrocarbon chain (derived from the fatty acid) and a polar head group.
- The non-polar tail is lipophilic (oil-loving).
- The polar head group is hydrophilic (water-loving).
Depending on the nature of the polar head group, they can be used in both oil-in-water (O/W) and water-in-oil (W/O) emulsions.
Used in cosmetic formulations due to their effectiveness and versatility. These include creams, lotions, sunscreens, makeup products, and hair care formulations.
Some examples of fatty acid-based emulsifiers include:
- Glyceryl esters: Glyceryl stearate
- Anionic emulsifiers: Sodium stearoyl lactylate
- Fatty acid soaps: Sodium stearate
Alcohol-based emulsifiers
Alcohol-based emulsifiers contain fatty alcohols as a key component in their molecular structure. They consist of a long, non-polar hydrocarbon chain (derived from the fatty alcohol) and a polar head group. In the case of fatty alcohol ethoxylates, the polar head group is formed by the addition of ethylene oxide units. This makes them more water-soluble.
They impart the following characteristics to the cosmetic products like:
- emulsifying properties,
- texture, viscosity, and spreadability,
- sensory properties, such as a smooth, non-greasy feel on the skin.
Alcohol-based emulsifiers can be used in both oil-in-water (O/W) and water-in-oil (W/O) emulsions. This depends on their hydrophilic-lipophilic balance (HLB) value. Fatty alcohol ethoxylates with higher HLB values are suitable for O/W emulsions. Those with lower HLB values are better suited for W/O emulsions.
Examples of alcohol-based emulsifiers include:
- Fatty alcohol ethoxylates: Laureth-23
- Fatty alcohols: Behenyl alcohol
Ester-based emulsifiers
Ester-based emulsifiers contain ester groups in their molecular structure. They provide versatility, stability, and ability to provide desirable sensory properties. Their structure consists of:
- A non-polar hydrocarbon chain derived from fatty acids or alcohols.
- A polar head group formed by the ester linkage.
Known for their stability and resistance to pH changes and electrolyte interference. Used in both oil-in-water (O/W) and water-in-oil (W/O) emulsions, depending on their HLB value.
Some examples of ester-based emulsifiers include:
- Sorbitan esters: Sorbitan monostearate, Sorbitan monolaurate
- Polyethylene glycol (PEG) esters: PEG-100 stearate, PEG-40 stearate
- Glyceryl esters: Glyceryl stearate
Protein-based emulsifiers
Derived from various protein sources, such as plants, milk, or other natural sources. Protein-based emulsifiers have both hydrophilic and lipophilic regions. Allows them to stabilize emulsions by reducing the interfacial tension between the oil and water phases.
Some examples of protein-based emulsifiers include:
- Lecithin and phospholipids (derived from egg yolk or plant sources like soy)
- Caseinates (derived from milk proteins)
- Hydrolyzed proteins (e.g., hydrolyzed wheat protein, hydrolyzed soy protein)
Depending on their composition and HLB, they can be used in both oil-in-water (O/W) and water-in-oil (W/O) emulsions. Lecithin and caseinates are commonly used in O/W emulsions. Hydrolyzed proteins can be used in both emulsion types.
Many protein-based emulsifiers are derived from natural sources. This makes them attractive options for natural and organic cosmetic formulations.
Polymeric emulsifiers
Polymeric emulsifiers are a good option for those looking for elegant and quick cold-process solutions. They are often sold as liquid polymer suspensions. These emulsifiers can create anything from lightweight sprayable milk to thicker, richer creams. This depends on what they are paired with.
While not for the natural market, these can be quite a sustainable option, due to:
- Their low addition rate
- The speed with which they can form an emulsion, and
- Their cold processing capabilities
Polymeric emulsifiers won’t work in every situation. Often these emulsifiers are acrylic acid polymers that tend to form complexes with cationic species.
In addition, the general salt tolerance of acrylates is low. This reflects the overall intolerance of ionic substances).
They have one big advantage over ionic and non-ionic emulsifiers. It is their ability to form highly stable emulsions with a very low level of polymer (with a non-polar or very slightly polar oil phase). This makes them the perfect emulsifier for a silicone-based emulsion, even those containing cyclomethicone.
Liquid Crystal Emulsifiers
Liquid Crystal Emulsifiers work on the principle of forming a lamella network in the cream. This most closely mimics the skin barrier. This facilitates the effective delivery of actives. Lecithin naturally works this way, as does Olivem 1000 and various other combinations available to purchase today.
Because of their skin-like structure, liquid crystal emulsifiers are often desired for their beautiful aesthetics.
While it is possible to create a range of textures using almost any emulsifier, depending on what goes into the rest of the formula, it would be reasonable to say that the liquid crystal generating emulsifier is the most foolproof way of creating a beautiful texture without too much additional work.
Silicone emulsifiers
Silicone-based emulsifiers are generally liquid at room temperature. There are two general structures for this class of emulsifiers.
- The first one is a rake silicone polyether in which the polyether segments are attached to a silicone backbone. It allows the addition of alkyl chains to increase their compatibility with organic oils.
- The other structure is an (AB)n silicone polyether, where the polyether segments are added within the silicone backbone.
These emulsifiers have an affinity for silicone and organic oils. This makes the oil phase flexible enough for the addition of other specialty silicones. Silicone emulsifiers help to reduce the cost of the overall formulation by emulsifying up to 80% water.
Moreover, water in silicone (W/Si) emulsifiers last longer and are wash resistant when compared to O/W emulsifiers. Silicone emulsifiers find uses in almost all skin care products.
Discover the complete range of emulsifiers based on their chemical composition available in our database.
Emulsion type
Oil-in-water emulsifiers
Oil-in-water emulsifiers create oil-in-water emulsions. In
oil-in-water (o/w) emulsion systems, oil droplets are dispersed in water.
- Oil is the internal/ dispersed phase whereas water is the external/continuous phase.
- O/W emulsifiers are more soluble in water than in oil.
- O/W emulsifiers have an HLB greater than 15.
Advantages & disadvantages of O/W emulsifiers
The emulsions produced with the help of oil-in-water emulsifiers have certain advantages and disadvantages discussed below.
|
Advantages |
Disadvantages |
- Oil-in-water emulsions have a good spreadability on skin.
- They are economical and can be easily manufactured.
- They have good physical stability.
- Are stable at temperatures even below 0°C.
- Oil-in-water emulsions provide a cooling effect to the skin as water constitutes the external phase of these emulsions.
|
- More vulnerable to microbial attack and bacterial contamination.
- Do not prove to be cost effective as addition of preservatives is required to prevent degradation of the formulation.
|
Examples of O/W emulsifiers
Listed below are few oil-in-water emulsifiers along with their main properties and applications.
|
Product name
|
INCI |
CAS
|
Applications
|
Main Properties
|
Emulsynt™ 1055
(Liquid)
|
PEG-8 PROPYLENE
GLYCOL COCOATE
POLYGLYCERYL-4
OLEATE |
9007-48-1,
977061-81-6
and
126645-98-5
|
Skin / Sun care
Hair care
Fragrances
Toiletries/
Make-up
|
- Acts as a water-in-oil, water-in-silicone emulsifier as well as auxiliary stabilizer for oil-in-water preparations.
|
HallStar® EGAS
(Flakes)
|
STEARAMIDE AMP
GLYCOL STEARATE
|
111-60-4
and
68951-62-2 or
36284-86-3
|
Skin / Sun care
Hair care
Fragrances
Toiletries/
Make-up
|
-
Acts as a bodying agent, co-emulsifying agent, emulsifying agent (o/w), emulsion stabilizing agent and viscosity stabilizer.
- Is plant derived / vegetal-based and biodegradable.
- Provides good electrolyte stability for both hair and skin conditioning emulsions.
|
HallStar® GMS SE
(Flakes)
|
GLYCERYL STEARATE SE
|
11099-07-3
and
593-29-3
|
Skin / Sun care
Hair care
Toiletries/
Make-up
|
- Acts as bodying agent, co emulsifying agent, emulsifying agent (o/w) and emulsion stabilizing agent.
- Is biodegradable, plant derived / vegetal-based.
|
HallStar® GMS SE/AS
(Flakes)
|
PEG-100 STEARATE
GLYCERYL STEARATE |
123-94-4,
9004-99-3
|
Skin / Sun care
Hair care
Toiletries/
Make-up
|
-
Acts as a bodying agent, co-emulsifying agent, emulsifying agent (o/w), emulsion stabilizing agent and viscosity stabilizer.
- Is plant derived / vegetal-based and biodegradable.
- Provides good electrolyte stability for both hair and skin conditioning emulsions.
|
Applications of O/W emulsifiers
Oil-in-water emulsifiers are used in personal care products like:
Water-in-oil emulsifiers
Water-in-oil emulsifiers help in producing water-in-oil (w/o) emulsions. In W/O emulsions, water droplets are dispersed in oil (oil encases water).
- The oil comes in contact with skin first providing more greasiness.
- These emulsifiers are more soluble in oil than in water.
- They have HLB between 2.5-6 are non-ionic or polymeric.
Emulsions produced by W/O emulsifiers aid in protecting and nurturing dry and dehydrated skin (moisturizing effect). Thus, these are brought to use in moisturizers, dry skin care, skin-nourishing lotions, etc.
Advantages & disadvantages of W/O emulsifiers
The benefits of water-in-oil emulsifiers are given below along with their disadvantages.
|
Benefits |
Limitations |
- Water resistant
- Lustrous and glossy
- Opaque and
- Great skin feel
- Smooth application
- Milder than o/w and do not harm the lipid bilayers in the skin
- Less susceptible to microbiological attack
|
- When applied , these may give a heavy and greasy feeling on the skin
- Often difficult to obtain stable W/O systems, addition of stabilizers may be required
|
Examples of W/O emulsifiers
Some water-in-oil emulsifiers are listed below along with their properties and applications.
|
Product name
|
INCI
|
CAS
|
Applications
|
Main Properties
|
Capmul® MCM C10
(Powder)
|
GLYCERYL CAPRATE |
26402-22-2 |
Skin care
Fragrances
Toiletries/
Make-up
|
- Glyceryl caprylate.
- Acts as water / oil emulsifier.
- Recommended for creams, lotions, ointments and lipsticks.
|
Elfacos® E 200
(Paste)
|
METHOXY PEG-22/DODECYL GLYCOL COPOLYMER |
88507-00-0 |
Skin care
|
-
Highly efficient emulsifier for water-in-oil systems.
-
Has a high water retention capacity that allows the formulation of light creams with a very high water content that do not leave the skin feeling greasy.
|
Cremophor® WO 7
(Liquid)
|
PEG-7 HYDROGENATED CASTOR OIL
|
61788-85-0 |
Skin care
|
- Used in W/O emulsions, particularly suitable for liquid and modern, soft preparations that are known as soft creams.
- Acts as a non-ionic emulsifier.
- Does not leave a noticeable fatty sheen on the skin but produce a visible cosmetic effect.
|
Dehymuls® PGPH
(Liquid)
|
POLYGLYCERYL-2 DIPOLYHYDROXY
STEARATE |
144470-58-6
|
Skin care
|
-
Acts as a W/O emulsifier.
-
Used in W/O creams containing greater fractions of high molecular oils, like vegetable oils.
|
Applications of W/O emulsifiers
Water-in-oil emulsifiers are used in personal care products like:
Hydrophilic-Lipophilic Balance (HLB)
While preparing an emulsion choosing an emulsifier can be cumbersome. HLB system was introduced to save time and stumble upon the right emulsifier(s) for an application. HLB stands for Hydrophile-Lipophile Balance. It is a numerical value assigned to emulsifiers that indicates:
their relative affinity for water (hydrophilicity) or oil (lipophilicity).
balance between the hydrophilic portion to the lipophilic portion of the non-ionic surfactant).
The HLB system assist you in making decisions about the types and amounts of emulsifiers needed to create stable products.
Between 1949-1954 Griffin developed a pretty robust yet simple HLB system. It is the standard upon which the Span and Tween pairings from ICI were arranged. The method produced a scale ranging from 0-20 indicating what percentage of the emulsifier was hydrophilic. The number given was the percentage hydrophilicity / 5 (so the maximum number 20 related to a molecule being 100% hydrophilic).
Every ingredient we use has a required HLB value assigned to it based on its physical properties. Emulsifiers are either oil or water loving.
Low HLB
Low HLB value of emulsifiers indicates:
-
Hydrophobic behavior - hating water (or lipophilic - oil loving). More of a lipophilic character.
- Low number of hydrophilic groups on the molecule.
- Considered water-in-oil emulsifiers.
Intermediate HLB
The nominal HLB range is usually 2 to 14, with a midpoint of 7 (or HLB balanced).
High HLB
High HLB value of emulsifier indicates:
-
20 being very hydrophilic - water loving (or lipophobic - hating oil). More hydrophilic in character.
- Large number of hydrophilic groups on the molecule.
- Considered oil-in-water emulsifiers.
A cosmetic emulsion can be stabilized by using emulsifiers that match up with the ingredients in the formula. Ingredients with low required HLB values need low HLB emulsifiers. Ingredients with high required HLB values need high HLB emulsifiers.
This simple system was expanded upon by Davie’s in 1957. He thought some weight should be given to the functionality of the chemical groups on the molecule.
-
This makes sense given the variety of structures available to give a hydrophilic character.
- This method is widely used today and is one of the reasons that ionic emulsifiers can be assigned an HLB value.
- It is also the reason that HLB numbers in 30’s is found (the maximum HLB in this system is 40).
While formulating both the emulsifier and the oils to be emulsified have an HLB attached to them. The emulsifiers have a real HLB whereas the oils have a required HLB.
It is widely accepted that the best emulsifier pairings are formed when a high HLB emulsifier is combined with a low HLB emulsifier rather than selecting the emulsifier with the exact HLB you want to achieve. This combination effect serves to best fill the interface surrounding the continuous and dispersed phase, leaving less room for gaps and therefore increasing stability.
Calculating HLB of a system
In the HLB system, an ingredient or combinations of ingredients that need to be emulsified are assigned a number and then an emulsifier having the same number is chosen to create an emulsion.
-
A lipophilic/oil-loving/non-polar emulsifier is assigned a low HLB number (below 9).
- A hydrophilic/water-loving/polar emulsifier is assigned a high HLB (above 11.0).
- The ones that fall in the range of 9-11 are intermediates.
Let's say for example we have a blend of emulsifiers to create an emulsion. To find out the HLB of the blend the following calculations can be carried out:
Values: 70% Emulsifier 1 having an HLB number 15, 30% Emulsifier 2 having HLB number 4.3
|
HLB Calculation |
|
Emulsifier 1 |
70% X 15 |
10.5 |
| + |
Emulsifier 2 |
30% X 4.3 |
1.3 |
|
HLB of Blend |
|
11.8 |
Origin
Natural emulsifiers
Natural emulsifiers, as their name says, are naturally sourced. Since their introduction to the cosmetic industry, they have received an overwhelming response. Thanks to the "global go-green" emphasis.
Natural emulsifiers in cosmetics are more susceptible to microbial attack. Hence, the formulation needs the addition of a preservative. They are not too effective as emulsifiers which call for their addition in large quantities. Though a natural emulsifier-containing formulation has an extra edge over others, it can have some serious repercussions on the skin of the end-user.
Being naturally sourced, natural emulsifiers in cosmetics can prove potential allergens to some individuals.
- Lanolin - sheep's water-free wool fat is a natural emulsifier that serves as a bond between water and oil. It is added to skin care creams.
- Lecithin is a natural emulsifier that can be used alone or in combination with other emulsifiers. They are usually based on chemicals called phospholipids and can be both plant an animal derived.
- Depending upon the quantity of lecithin added, a formulator can achieve the desired consistency in a lotion.
- It is majorly used in skin care formulations due to its emollience/ moisturization effect.
- For hair care applications, in addition to lecithin, pectin and glycerin is also used.
- Beeswax, another natural emulsifier finds good use in lip balms, lipsticks, ointments, etc.
Product
name
|
INCI |
CAS
|
Applications
|
Main Properties
|
ALKOLAN® CD 80
(Liquid)
|
PALM KERNELAMIDE DEA |
68155-07-7 |
Skin care
Hair care
Sun care
Fragrances
Toiletries
|
- Acts as a thickener, foam stabilizer, re-fatting agent, detergent, emulsifier and solubilizer for fragrances and essential oils in the formulation of personal care products.
- Exhibits emolliency and neutralizing properties.
|
Phoenotaine® C-35
(Liquid) |
SODIUM COCAMIDOPROPYL PG-DIMONIUM CHLORIDE PHOSPHATE |
83682-78-4 |
Skin care
Hair care
Toiletries
|
-
Used as extremely mild surfactants, especially in baby products such as shampoos, bath and shower gels, body wash, bath beads, and products used in personal care.
|
Phytocompo™ -PP
(Powder) |
GLYCINE SOJA STEROLS
HYDROGENATED LECITHIN
|
92128-87-5,
68555-08-8 |
Skin care
Hair care
|
-
Acts as a natural emulsifier.
-
Enhances barrier properties, moisturizes skin and provides a unique skin feeling.
-
It can be used in synthetic surfactant-free products.
|
Lecinol S-PIE
(Powder) |
HYDROGENATED LECITHIN |
92128-87-5
|
Skin care
Hair care
Sun care
Fragrances
Toiletries
Decorative/
Make-up
|
-
Used in cosmetics.
-
Possesses good heat and oxidation stability compared to natural lecithin.
|
Synthetic emulsifiers
Synthetic emulsifiers are produced through chemical reactions of various raw materials such as:
-
Fatty alcohols and fatty acids,
- Ethylene oxide, and
- Other organic compounds
The synthesis allows for precise control over its chemical structure and properties. Used in cosmetic formulations due to their consistent quality, availability, and ability to meet performance requirements.
Some examples of synthetic emulsifiers include:
-
Ethoxylated emulsifiers: Polysorbates
- Anionic emulsifiers: Ammonium lauryl sulfate
- Polymeric emulsifiers: Carbomer
- Silicone-based emulsifiers: Dimethicone Copolyols, Alkyl Dimethicone Copolyols
Discover the complete range of emulsifiers based on their origin available in our database.
Physical state
Based on their physical state, emulsifiers can be classified into two main types:
Solid emulsifiers
These are emulsifiers that are solid or waxy at room temperature. They contribute to thickening and stabilizing emulsions while providing a rich, creamy texture.
Examples include:
- Fatty alcohols - Cetyl alcohol, Stearyl alcohol
- Emulsifying waxes - Glyceryl stearate citrate
- Certain fatty acid esters
Liquid emulsifiers
These are emulsifiers that are liquid at room temperature. They are used to stabilize low-viscosity emulsions. They can contribute to a light, non-greasy feel in formulations.
Examples include:
-
Polysorbates
ethoxylated emulsifiers - Ceteareth-20, Steareth-20
- Certain polymeric emulsifiers
Discover the complete range of emulsifiers based on their physical state available in our database.
Managing Water and Oil Phase Interactions
Managing Water and Oil Phase Interactions
Importance of chemistry of the water phase
An emulsion is a combination of two immiscible phases held together. This looks and feels like magic to many! What is really going on is a physical rearrangement of components, all trying to get themselves into a position that means they are exerting the lowest possible amount of energy – those dispersed phase droplets are lazy!
The dispersed and continuous phases are influenced by everything that comes into the formula. Some things are more disruptive than others.
Impact of surface tension
The surface tension between oil and water is so high that they don’t mix unless you add a surfactant (emulsifier in this situation). We understand that and have different types of emulsifiers that we could add. But do we understand what other ingredients do to the product’s surface tension?
Preservatives and solvents can dramatically alter the surface tension between the oil and water droplets. As we see with emulsifier, some reduction in surface tension is required to facilitate the development of an emulsion. But in other cases, the changes are catastrophic and can result in viscosity and emulsion collapse.
Glycerin, Propylene Glycol, and Ethanol are common additives in a cosmetic product. They can all impact surface tension. All of these ingredients decrease the polarity of the water phase. This thus decreases the changes depending on the quantity of additive present. Although the relationship between dose and effect is not strictly linear.
Reducing water phase polarity loosens the grip the water has on the dispersed phase somewhat by toning down the intramolecular forces that make water behave as it does – Van Der Waals, Dipole-Dipole and hydrogen bonding.
All emulsifiers depend on these forces to some degree to stabilize the product. The Ionic emulsifiers depend on them more strongly. Thus, they are most likely to be influenced by their presence.
Impact of ions
We often talk about salt and saltiness in formulating, but what we really need to talk about is the ionic strength of the continuous phase.
The swapping of demineralized water for seawater might cause formulary issues. We are less likely to accept that the actives we carefully measure into our water phase are doing the same. Be they acids, bases, or salts, an ion-rich water phase, can cause havoc, for the stability of a product.
Ionic charge in the water phase can help increase intramolecular bonding. It can also help in the formation of an electric double layer around the dispersed phase. This increases stability but things can go too far, especially with:
- Divalent salts such as zinc
- Strong acids, and
- Oxidizing agents such as glycolic and peroxide
Adding too many ions into the continuous phase
will give the product a sticky/tacky/salty feel when applied
|
In general, the cosmetic chemist is looking to minimize chemical reactions in their formula. So any addition of ions should be thought of as fueling the fire of chemical rebellion. Every emulsion has its limits, plus adding too many ions into the continuous phase will give the product a sticky/tacky/salty feel when applied.
Can oil phases get tricky to handle?
When compared to vegetable oils, silicones demonstrate practically no polarity. They also have very different chemical structures – flexible chains vs bulky triglycerides. Because of these differences, silicone fluids tend to mix poorly or not at all with vegetable oils in the same formula. Some examples of silicone fluids include dimethicone and cyclomethicone.
If the formulator wishes to create a silicone-rich emulsion, he should consider the influence of this low polarity.
Steps to reduce the polarity of the continuous phase would increase stability. It will take some of the pressure off the emulsifier as the surface tension between the two phases decreases.
Silicone emulsifiers are available from the major silicone manufacturers. It should be the first port of call for all those looking to create a silicone-dominant emulsion. Especially where the silicone phase will be large or even dominant. Having said that, with careful consideration, it is also possible to create a silicone-rich emulsion with non-silicone emulsifiers. This is possible if we consider the chemistry of the whole product.
Is your emulsion going to be salty, acidic, or basic? Or does it contain a high proportion of solvents that are less polar than water? Or does it contain Hydrogen Peroxide? If so, the best starting point is non-ionic.
The regulation requires that any cosmetic product has guaranteed stability & integrity until shelf-life. It takes lots of time to run stability tests. We all want to avoid as many stability issues in the final development steps which would imply starting everything all over again!
Factors Influencing Emulsifier Selection
Factors Influencing Emulsifier Selection
There are four main factors that deserve consideration:
-
Marketing/ Product Positioning
- Performance
- Physical Character
- Chemistry
As Cosmetic Chemistry is an applied science, it is appropriate to start with the marketing as this is the main reason for us embarking on this formulation work.
Marketing
Emulsifier-free claim
An emerging niche of ‘emulsifier-free’ creams designed around the philosophy that the emulsifier, being a surface-active ingredient, may be a source of irritation for very sensitive skin and that avoiding the use of an emulsifier may make the product more suitable for this demographic.
Now, this may or may not work out to be true. But nevertheless, the concept is of interest as there is some truth in the idea that surface-active ingredients (of which emulsifiers are a part) can contribute to a product’s irritation potential.
So, if you don’t use an emulsifier to hold the oil and water together, what do you use?
Small amounts of oil can be held in suspension with the use of thickeners/ stabilizers such as Carbomer, and even xanthan and sclerotium gums to a lesser degree. These aren’t emulsifiers and neither are they forming an emulsion, more of a suspension. But if the oil phase is light and dispersed well enough, these products can be made stable through steric hindrance – the oil droplets are caught up, as if in a fishing net!
Sometimes bentonite clays can also be used in this way. They bring opacity to the formula. They also provide an electrical repulsion layer into the structure to help repel agglomeration of the dispersed phase.
Another option in this space is a modified acrylate copolymer such as Acrylates/Beheneth-25 Methacrylate Copolymer.
- Although this polymer is best suited to surfactant formulations, it does have a role to play in leave-on skin care.
- It is tolerant to relatively high levels of salt and other water-phase destabilizers. This makes it a versatile choice for the ‘emulsifier-free’ concept developer.
The fact that the polymer can stabilize a reasonably sized oil phase while remaining ‘emulsifier-free’ paired with its low use levels adds to the cost efficiency of this solution. Another interesting feature of these polymeric ‘emulsifier-free’ ingredients is their ability to be sprayed. This opens up new doors for the formulator and marketing department.
What if you are looking to create something a bit richer and with an oil phase more typical of a traditional moisturizer?
-
Modified lecithin chemistry has become the accepted technology in the ‘no emulsifier’ space. This is especially because these lecithin fractions often have lipid-enhancing properties. It can be sold on their ‘skin compatibility’ and moisture-binding powers. In addition, the phospholipid structure also lends itself to active delivery given how similar in structure they are to human cell membranes (well at least in terms of their chemical constituents).
- Lecithin chemistry forms a liquid crystal network in the continuous phase. It traps and interacts with the dispersed phase in an ultra-stable and skin-compatible 3D structure.
A number of companies are now offering a range of modified lecithins. They are suitable for everything from light hypoallergenic milk formulations to super-rich balms which should please marketing departments all over the world. But from a chemist's perspective, it is hard to see how these ingredients have managed to escape the ‘emulsifier’ tag.
Ingredient origin and ethics
Another important consideration for the general public and formulators alike is ingredient sustainability and/or ethics. There is a steady yet growing interest in ‘palm oil-free or sustainable palm’ concepts, the achieving of which is surprisingly difficult. That said, making an emulsion without adding any palm derived ingredients used to be easy – just use petroleum derived chemicals – but these days that is just as unacceptable for a growing number of brands.
The reality is, our enthusiasm for embracing the natural revolution has increased demand for vegetable-based feedstock and those of us who have been in the industry for a while know that means either palm (orang-u-tan habitat) or Rapeseed/ canola (pesticides and bees).
Demand for Vegetable-based Feedstock has Increased in the Cosmetics Industry
So today while it is still not easy to create palm free emulsion it is not impossible too, given that our previous ‘emulsifier free’ examples are predominantly palm free (lecithin phospholipids are frequently made from Rapeseed, Egg, Soybean and/or Sunflower).
In fact, it would be fair to say that the hardest thing about making a palm free emulsion today is not over which emulsifier to choose, but which supporting ingredients can be used to increase stability, viscosity (without gumminess) and overall skin feel.
INCI name – It has to look good on the label!
Under the guise of marketing issues, the issue of INCI names also comes up here. While ingredient manufacturers do have to abide by a ‘truth in marketing’ legislation when they apply for their INCI names. They can’t just make them up.
The reality is that a natural sounding INCI will sell more and have better shelf appeal than a more chemical sounding ingredient. This has hit home and that can be both good and bad.
In some cases, we have very average ingredients (in terms of performance) becoming popular. This is because they have a nice name while outstanding ingredients (that are still natural in many cases) are overlooked. Click here to get more information on cosmetic ingredients from SpecialChem's INCI Database Directory!
Cost considerations
Another important factor in the marketing basket is price. Emulsifiers can make quite a dent in the formula budget. When comparing something natural to a stock-standard petroleum-based emulsifier you can be looking at anything from three to five times the price which of course has to be justified.
In many ways this is the acid test – will customers put their money where their ethical mouths are or do we have to sell them another benefit?
Blending different technologies together can be a good way to increase performance while managing price. This philosophy has kept many of the older emulsifier’s options such as glyceryl stearate SE alive and selling well.
Performance
Performance benefits of different technology have been looked at more in the chemistry section. But seeing from some of the claims related to emulsifier-free formulations, the ingredient that holds the oil and water together is, in many cases expected to do so much more besides.
When the Olive-derived Emulsifier Olivem 1000 first came onto the market there was a great deal of interest in its ability to:
-
act as an active delivery system
- make an emulsion possible
This contributed to the ‘emulsifier-free’ marketing tagline (it isn’t an emulsifier; it is an active delivery system). It also helps the cosmetic chemists deliver oil-soluble actives deep into the skin (theoretically).
This important dual functionality contributed to the immediate success of this technology. The success continues today in spite of the ingredients' high price point compared with older technologies. For example, cetearyl alcohol will form liquid crystal structures for a fraction of the price!
In terms of integrating new emulsifier technology into the laboratory these days, the real question isn’t the price. But it is how many benefits one gets for that price. The following benefits are possible thanks to the combination of science and nature:
- Water resistance
- Barrier protection
- Long-wear characteristics
- Increased dispersion of actives
- Viscosity boosting, and
- Rheological benefits
Physical Character
Something that we may overlook when considering price is the emulsifier’s physical form. This is because we often just think of emulsions as hot-process items and so the form of the emulsifier is not really a talking point. But it doesn’t have to be that way.
Electricity prices are rising in many countries and even those with cheap power aren’t in the habit of wasting it. So liquid emulsifiers that can be used in cold-process applications can help the formulator to tick a few boxes from sustainability to the economic benefits of saving time and money.
The range of liquid emulsifiers is steadily growing and is worth a look, especially for markets that demand an ultra-light touch finished product with little to no wax or butter content.
Chemistry
Of course, we couldn’t talk about emulsifier selection without talking about the chemistry. The emulsifier is the heart of the formula and while it may often seem like, today the chemistry has all been done for you, as mentioned in the beginning, there are some very challenging problems that await the professional cosmetic chemist that only an appreciation of the underlying chemistry will help solve! Don't let complicated emulsifiers selection rules hinder attainment of your perfect formulation!
How to evaluate emulsifiers?
How to evaluate emulsifiers?
A very simple formula based on a common non-ionic emulsifier Cetearyl Alcohol and Cetearyl Glucoside has been developed. This formula was then replicated with different emulsifiers, one from each different class (except silicone). The products were evaluated by an expert panel of five people. They checked their viscosity before being evaluated under the microscope.
The formula and feedback are not presented to help sway a decision towards or away from a particular type of emulsifier. Merely it is to illustrate a point, that the emulsifier can impact everything from viscosity to feel, efficacy to stability. It also demonstrates the importance of optimizing the whole formula to get the most out of the emulsifier of choice. Plus, there is always room for pairing up on technologies or trying something new!
So, the only difference between these formulations is the emulsifier except for the cationic version which was incompatible with the thickener Acacia and Xanthan gum blend. In the cationic, a cationic guar has been used at the same level. This could be seen from the table below:
|
Formula
|
Skin Feel
|
Viscosity @ 3.0
Spindle
|
| Cationic (Brassicyl Isoleucinate Esylate (and) Brassica Glycerides (and) Brassica Alcohol) |
Thin, high spreading, slightly tacky to touch at first drying to
powdery |
19,380 |
| Anionic (Potassium Cetyl Phosphate) |
Silky, takes a while to absorb, feels substantive after drying. |
90,630 |
| Non-Ionic (Cetearyl Alcohol, Cetearyl Glucoside) |
Easy to rub in |
56,250 |
| Mixed Anionic/ Non-ionic. (Glyceryl Stearate (and) Cetearyl Alcohol (and) Sodium Stearoyl Lactylate) |
Easily absorbed |
74,690 |
| Non-Ionic Synthetic (Cetearyl Alcohol, Ceteareth-20) |
Very thick and creamy, light after feel |
160,600 |
| Polymeric (Acrylates/C10-30 Alkyl Acrylate Crosspolymer) |
Ultra-light, quick break and high spreading. Tacky on drying. |
15,310 |
| Liquid Crystal Emulsifier (Cetearyl Olivate, Sorbitan Olivate) |
Rich waxy texture, slow spreading |
82,190 |
| HLB balance (Sorbitan Monooleate, PET-20 Sorbitan Monostearate) |
Very light and spreadable |
13,440 |
Base formulation used could be observed from the table shown below:
|
Phase
|
Ingredient
|
%
|
200g
|
Function
|
|
Water Phase |
Deionized Water |
71.95 |
143.9 |
Solvent |
|
Acacia and Xanthan Gum |
0.4 |
0.8 |
Thickener/ Stabilizer |
|
Glycerin |
3 |
6 |
Humectant |
|
EDTA |
0.1 |
0.2 |
Chelating Agent |
|
Oil Phase |
Jojoba Oil |
8 |
16 |
Emollient |
|
Shea Butter |
8 |
16 |
Barrier Protection |
|
Squalane |
2.5 |
5 |
Emollient |
|
Emulsifier of choice |
3 |
6 |
Emulsifier |
|
Cetearyl Alcohol
|
1.25 |
1.25 |
Emulsion Stabilizer |
|
Finishing Touches |
Natural Vitamin E |
0.5 |
1 |
Antioxidant |
|
Perfume |
0.3 |
0.6 |
Aroma |
|
Preservative
|
1 |
2 |
Broad Spectrum
Preservative |
| TOTAL |
|
100 |
200 |
|
About Amanda Foxon-Hill
Amanda Foxon-Hill is a consultant Chemist and Science Communicator with over 14 years of experience in the global cosmetics industry. She is a writer, after dinner speaker, strategist and lecturer in all aspects of cosmetic science and runs a successful consultancy practice under the name of Realize Beauty.
Amanda’s key skills are in networking and communicating ideas and opportunities both on a business to business and business to market level. She is an advocate for green science and through her team funds research into the development of more sustainable manufacturing practices.
About Nick Morante
Nick Morante is currently a Senior Chemist at IFC Solutions (formerly International Foodcraft) in New Jersey where he works with many types of colors and additives for both the food and cosmetics industries.
He has over 40 years of experience in the formulation of cosmetics, personal care products and makeup products. Prior to joining IFC, Nick was a consultant to the cosmetics industry for over 10 years providing custom formulations for clients as well as giving presentations and seminars to various companies and organizations within the cosmetics industry providing guidance in the practical use of color in consumer products.
He is current an adjunct faculty member at Fairleigh Dickinson University’s School of Natural Sciences in Hackensack, NJ where he is an instructor in the Master of Science Program in Cosmetic Science.
Nick also spent over 30 years in Research and Development at The Estée Lauder Companies where he was both a formulator and laboratory manager in the corporate makeup and hair care departments. He was also in charge of the Color Science Laboratory where he was responsible for color measurement and spectrophotometric analysis of finished products, ingredients and human skin as it relates to color that is used in various cosmetic products, as well as developing testing protocols and methodologies for many color applications.
Nick holds a Bachelor of Science degree from The New York Institute of Technology. He has taken numerous continuing education courses in the area of cosmetic science. He is a long time member of U.S. The Society of Cosmetic Chemists and has been active both on the local and national levels having served on the executive committee for the Long Island Chapter and on the National Board, serving as Area Director and National Secretary. He has been elected a Fellow of the Society and is an instructor for the Society’s Continuing Education Program (CEP) Program in the area of color and makeup formulation problem solving and troubleshooting.
He has given many seminars and presentations worldwide as well as to the SCC, CTFA and HBA. He has been awarded numerous patents and has contributed many articles and papers and authored chapters in numerous cosmetic, technical and beauty publications and texts.