Surfactants are such fun ingredients to formulate with and they are so versatile. You can use them for a range of applications & Products… shampoos, facial wash, body wash, surface cleaners, foaming products and so much more.
But before we dive into formulating, mixing, and making products there is a little bit of chemistry we need to understand.
Surfactants lower the surface tension between two liquids and act as detergents, wetting agents, emulsifiers, foaming agents, and dispersants. They have good cleansing and foaming properties. Surfactants are classified as either primary or secondary surfactants and have different chemical structures (anionic, non-ionic, amphoteric and quaternary)
A key to utilizing surfactant’s unique properties lies in understanding how and when to use them.
The Polarity of Molecules
To understand surfactants, it’s first important to understand a property of all chemicals, polarity.
Basically, compounds can be classified as polar and non-polar.
Non-polar molecules like oils have enough electrons in them to make them stable.
Polar molecules, like water, have an imbalance in electrons which makes them attracted to other imbalanced molecules.
The important part to understand here is that Polar molecules are attracted to other polar molecules while nonpolar molecules are attracted to other nonpolar molecules. Like attracts like
For example: Water and Oil will not mix.
So, we need some help, that’s where surfactants come in.
What are surfactants?
The word surfactant is short for “surface active agent” and has a hydrophilic (water-loving) head and a lipophilic (oil-loving) or hydrophobic (water-hating) tail. This means it can bring things together like oil and water. So an emulsifier, like emulsifying wax or BTMS, is a surfactant.
To recap: There are four technical terms about surfactant molecules
Hydrophilic – the “water loving” or polar part of the molecule
Hydrophobic – the “water hating” or nonpolar part of the molecule
Lipophilic – the “oil loving” part of the molecule (same as hydrophobic)
Lipophobic – the “oil hating” part of the molecule (same as hydrophilic)
If you examine a surfactant molecule like Sodium Lauryl Sulfate you’ll see that one end of the molecule is hydrophilic and the other end is hydrophobic.
This dual compatibility is what makes surfactants useful for cosmetic formulators.
Classification of Surfactants
- Anionic – negative charge
- Cationic – positive charge (ionized positive charge)
- Nonionic – neutral
- Amphoteric – positive and negative (positive in acidic environments and negative in alkaline environments)
- Anionic Surfactants
Anionic surfactants have a negative charge to the water-loving head, called hydrophilic. Anionic surfactants perform the highest foaming and cleansing actions. They can also build viscosity. Anionic surfactants may be harsh on the skin and hair. Cold process handmade soap is anionic from the reaction of the fats with sodium hydroxide but cold process soap is not harsh on the skin if there is extra oil in the soap. A lot depends on the formulation and the ingredients in the formulation.
- Nonionic Surfactants
Nonionic surfactants have no charge to the water-loving head. Nonionic surfactants are one of the gentlest surfactants but they produce very little foam. They are usually combined with other surfactants to boost foam. Nonionic can act as solubilizers and assist with dispersing essential oils.
- Cationic Surfactants
Cationic surfactants have a positive charge to their water-loving head. The positive charge creates adherence to the net negative charge of hair. Cationic surfactants are used in conditioning shampoo and hair conditioner to adhere to the hair and not rinse off the hair, allowing the conditioner to provide conditioning and leave the hair smooth, soft, silky and with less static electricity. Cationic surfactants are good in formulations for co-wash and 2-in-1 conditioning shampoo. Cationic surfactants do not combine well with anionic surfactants.
- Amphoteric Surfactants
Amphoteric surfactants can have a negative or positive charge or no charge depending on the acid or alkaline environment. Amphoteric surfactants are generally used as the primary surfactant in mild shampoo formulations.
- Active Surfactant Solids
Surfactants contain a detergent and water (glycerin can be part of the water). The detergent is the solid matter and referred to as active. The raw material supplier states the active in % for each surfactant. The supplier may state it as actives, active matter, active substances, solids or activity. For example, in decyl glucoside, generally it is 55% active (solid), the remaining is 45% water.
DO NOT go mixing cationic and anionic surfactants as they may not work so well together.
We never use just one of these types of surfactants as each brings something to the party. For instance, an anionic surfactant will offer good bubbles, foam, and lather but might be a bit harsh. So we add some amphoteric surfactant to the mix and this will make it milder and thicker. I like to add a cationic surfactant to my shampoos and body wash to offer some conditioning at about 2 to 3% maximum, and I’d include a non-ionic if I had a large amount of oil I wanted to emulsify, say for a shampoo for dry hair.
THE ACTIVE MATTER of a surfactant:
How “strong” do we need our detergent to be?
This of course depends on what we aim to make: if we are going to make a bubble bath it will need to have a higher washing ability than a face wash, which should, on the contrary, be very gentle and delicate.
The washing ability of a detergent is determined by its “Active Matter” coefficient: every surfactant has an “active matter coefficient” which is a number in percentage (for example the SLES coefficient is 27%) and this tells us “how much active washing substance there is in our SLES… and in this case it is 27%”.
This is because the liquid surfactants are usually made of the real surfactant and water (so the active matter is not 100%).
Generally, the active matter of surfactant we want in our detergent depending on its aim is this:
– Face wash – lower than 10%
– detergent for intimate use – around 5%
– shampoo – between 10% and 15%
– shower gel – between 18% and 20%
– bubble bath – between 20% and 25% (this is because the bubble bath should go directly in the water while the shower gel is supposed to be rubbed directly on the skin)
In a formulation, a single surfactant will result in a more harsh product than an equal “active matter %” formulation made with different surfactants.
If you mix 2 or more surfactants together, you will have milder results than using one surfactant alone.
A particularly happy mix is SLES with a betaine (cocamidopropyl betaine) because not only the betaine lowers the harshness of the SLES, but it also thickens the solution.
Generally, when formulating you should use:
– anionic or non-ionic surfactant; it is the surfactant which we will add in our detergent at a higher %.
– amphoteric surfactant; it will make the first surfactant milder.
– extra surfactants: these are used in very low percentages and are added to improve the lather or the consistency of the detergent
Now finally to THE FORMULATION
For a successful cleaner formulation, you need to determine :
- On 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
When constructing a cleansing formula, one needs to divide the formula into functional buckets:
- 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 –
- Emolliency & Moisturization (e.g., glycerin, fatty acid esters, polymers),
- Rinse-off aids
- UV Stabilizers for colorants
- Pearlizing agents
Water phase and usually it contains water and glycerin (remember glycerin is important to keep our products hydrated, this is because glycerin is highly hydrophilic).
In case you want to add xanthan gum you have to add it now
Phase B we have most of the surfactants: add the surfactant at a higher percentage (which is usually an anionic surfactant) and one by one we add the “extra surfactants” which are usually the non-ionic ones.
IMPORTANT: do not add now the amphoteric surfactants (generally the betaine) or your detergent might get ruined.
One important thing to notice is that once you add a surfactant to another you are supposed to mix slowly and combine them very well because you add a third one.
Now it is time to pour Phase A slowly into Phase B and mix.
This time we only use a spoon to mix, paying attention to not make too many bubbles
This is the phase where you add the amphoteric surfactant and usually, your detergent gets thick here.
If this does not happen you can try adding 1% salt.
In the case of shampoo, you also are supposed to add at this moment all the hair conditioner substances.
Example: let’s learn how to calculate ASM to formulate a shower gel.
We want an Active Matter of around 18%. ( not too foamy but just enough to wash well)
We will use these surfactants:
– Sodium Lauroyl Sarcosinate (Concentration 29%)
– Cocamidopropyl Betaine (Concentration 36%)
– Lauryl Glucoside (Concentration 52%)
To obtain 18% Active Surfactant Matter:
We can choose which share of the total ASM (active surfactant matter) we want to give to each surfactant.
Sodium Lauroyl Sarcosinate 10% (we will use 10 % SLS – remember you can choose how much you want, that is why it is important to know its properties.)
Cocamidopropyl Betaine 5%
Lauryl Glucoside 3%
Total ASM = 18%
Now we need to calculate the effective grams of each surfactant that we need to add to our shower gel formula:
We divide the share of each surfactant by the ASM of the surfactant (in decimals: the ASM of each surfactant is a percentage so if it is 29% we divide per 0.29 OR we divide per 29 and multiply the result for 100… up to you).
Sodium Lauroyl Sarcosinate (29%) = 10/29*100 = 34,44 (you can add 34.50 gr)
Cocamidopropyl Betaine (36%) = 5/36*100 = 13.88 (you can add 13.50 gr or 14 gr)
Lauryl Glucoside (52%) = 3/52*100 = 5.76 (you can add 5.5 gr)
Surfactant technical infomation
Cocamidopropyl betaine (Amphosol CG): Amphoteric. A humectant. Good foaming properties. Good flash foam and foam stabilization properties. Adding this amphoteric to an anionic mix will reduce the harshness of the other surfactants and changes the viscosity. It is a good anti-static for hair. Poor to mild cleanser. Good where mildness is vital — babies or sensitive skin — but primarily used as a secondary surfactant.
SLSa (sodium lauryl sulfoacetate): Anionic. Powder form. Mild and non-drying (I disagree with the “non-drying
” part.) High volume and long-lasting foam. Provides LOTS of bubbles.
Decyl Glucose (Plantapon 2000): A mild surfactant made from glucose and coconut oil. Would be great for mild cleansing. It does have a high pH, so if you have a pH meter or pH strips, use them when formulating with this product! It is plant-derived, so it is suitable for vegan products and is 100% biodegradable. (As a note, I’m not sure why Plantapon is described as a vegan because it’s not like the other surfactants are made of pork!)
|active matter: 30%
|Shampoo, Bar Soap, Body/Facial Cleansers, Foam Boost, Liquid Soap, Sulfate-Free, helps bring down pH
|active matter: 55%
|Baby Shampoo, Low irritation shampoos/washes.
|active matter: 51%
|100% naturally derived feedstocks, biodegradable, mild. Excellent foaming & cleansing properties.
|active matter: 50%
|100% natural, renewable, plant-derived feedstocks, biodegradable, great foaming, and cleansing. Sable in low pH applications.
|Sulfate Free Nonionic
|Polysorbates 20, 60, 80
|Solubilize essential and fragrance oils.
|Sodium Cocoyl Isethionate
|active matter: 87%
|solid surfactant; rich lather with easy and complete rinse-off; excellent tolerance of hard water and leaves no soap scum. Mostly used in shampoo and conditioner bars, and syndet bars.
|Sodium Lauryl Sulfoacetate
|5–7.5 (5% solution)
|Top performing, mild powder surfactant for making low irritation bath foam products.
These glucosides are all quite similar, the main molecular difference being the length of their carbon chains. They have slightly varying degrees of foam and longevity but can generally be substituted for one another in a simple surfactant recipe.
For a face wash, go for a quick-foaming, low viscosity surfactant such as decyl glucoside, supported with coco betaine.
For a shampoo, go for a thicker, more stable foamier such as lauryl glucoside, supported with a secondary surfactant and coco betaine.
Everyday functional uses of surfactants include:
1 – Combine oil and water
One of the most useful things surfactants allow you to do in your formulations is to blend oils and water. When you want to deliver occlusive agents and emollients to the skin, surfactant emulsifiers let you do that in a way that feels great and spreads easily. If you want to deliver a light coating of oil to hair, emulsifiers let you do that too. Nearly every cosmetic on the market uses some type of emulsification system.
2 – Cleaning
Soap, which is a surfactant made by the saponification of fatty acids is the most widely used surfactant. Surfactants work as cleansing ingredients because they are attracted to surface non-polar dirt particles. They can surround those particles, lift them off the surface allowing them to be rinsed away. If you formulating a cleaning product, you’ll need some surfactant.
3 – Foaming
When formulating a cosmetic product that foams, you’ll want to include a surfactant. Foam is created when there is mechanical agitation to a system and the surfactant molecules stabilize the surface of trapped air.
4 – Conditioning
There are a few surfactants that work great as conditioning materials. These are cationic surfactants and include things like Cetrimonium Chloride or Behentrimonium Chloride. These materials have long fatty acid backbones which can provide the smoothing and conditioning benefit, but they have a positively charged head group that is attracted to the negatively charged damaged protein in hair. They stick to the surface and provide the conditioning effect.
5 – Spreading
A surfactant will help your product spread out on the surface of hair or skin. When placed on the surface of the skin the surfactant molecules act like tiny ball bearings allowing the nonpolar molecules to easily spread over the surface.
6 – Solubilizing
This property is related to emulsification, but it works on a smaller scale. When blending a nonpolar ingredient like a fragrance or essential oil into a system that you want to remain clear, you need to use a solubilizing surfactant. The solubilizer will surround the nonpolar molecules and create tiny clear particles.
7 – Opacifying
This is the opposite of solubilizing. While surfactants are compatible with both oil and water, they aren’t all compatible to the same degree. There are some surfactants such as Glyceryl Stearate which will mix through a system but will create particles that are large enough to bend light and be seen by whoever is using the product. This is called pearlization and is a way to make your products opaque or pearly looking. It’s very popular in moisturizing shampoos and body washes.
8 – Thickening
Surfactants are also able to thicken a product. One of the primary thickening ingredients you’ll find in cleansing formulations are the surfactant system. There is no additional thickening needed. You just need to control it with the appropriate level of salt.
9 – Reduce irritation
Some surfactants can cause irritation, but there are other surfactants that can be added to your formulation that will actually reduce irritation. So, if you’ve created a formula that works great but is too irritating, include one of the nonionic surfactants that can reduce irritation.
10 – Anti-microbial
Surfactants have the ability to disrupt any system in which there is a polar molecule and a nonpolar molecule. Microbe cell walls and membranes are made up of phospholipid bilayers. Since microbes are made up of cell membranes and walls surfactants can break those down and kill the offending microbes. So, in some circumstance you can prevent microbial contamination by including a surfactant in your system.
Formulating with Surfactants ( Formulations to be added soon)
Foaming Bath Whip
Fizzy Foaming Bath salts
Foaming Bath Powder