Is soap a surfactant?
Posted on 24th July 2020 at 21:52
Is soap a surfactant?
In this article we're going to look at: whether soap is a surfactant, break down how surfactants work, plus we've created some helpful infographics to show you simply what surfactants look like and how they work. Here is a list of the topic's we're going to cover in this article;
First of all let’s talk about what a surfactant is and why it’s important to know if you’re using soap with a surfactant in.
A surfactant is shorthand for ‘surface active agent’ and is a chemical compound that can bond to both water and oil. This is similar to an emulsifier, which can allow water and oil to mix.
The purpose of a surfactant is to remove dirt from a surface such as a countertop, sink or even skin, as they are used in many skin cleansing products.
When you put surfactants under a microscope they look like tadpoles. The head of a surfactant, also known as the hydrophilic portion of the surfactant, loves water and is easily soluble within water. The tail of the surfactant, also known as the lipophilic portion of the surfactant, can easily bond to oils.
With properties like this you can see why these surfactants are used to mix oils and water together. For instance, in the case of a shower gel that is scented using essential oils, the surfactant added to water can also bond to the essential oils and mix together.
If there was no surfactant used, then the oil would sit on top of the water and not mix together well. This is why surfactants are present in most, if not all liquid soaps and detergents.
How do surfactants work?
A surfactant works by bridging the gap between a water molecule and an oil molecule. The long tail of the molecule which loves oil, can penetrate the barrier between oil and water. This allows the oil or fat to be broken down and absorbed into the water molecules.
Surfactants work by decreasing surface tension between two molecules. For instance in the example of using a surfactant in laundry, the surfactant decreases the surface tension of the stain molecules on the clothes. This allows the water and surfactant to mix easily with the stain and remove the stain from the clothes.
Surfactants are used for a variety of reasons; however, the main reason is they work for their desired purpose in reducing surface tension and interfacial tension between water and oil molecules, allowing them to mix easily.
Is soap a surfactant?
So now you've had an introduction to surfactants and how they work, the question you want to know if soap is a surfactant.
Soap is most definetely a surfactant. It has the all the key features of a surfactant which are a water loving end and an oil loving end of the molecule which can bond to both oil and water simultaneously. Soap also reduces surface tension between different molecules which is another key feature of a surfactant.
Soap was the original manufactured surfactant used by humans. Soap perfectly makes up the components of a surfactant. Soap is made when you mix fatty acids (attached to carboxylic acid), most commonly found in oils, fats and butters with an alkali.
The two most common alkali’s used for soap making are sodium hydroxide and potassium hydroxide.
When you mix these two components of soap together the fats also known as triglycerides because of the three fat molecules attached to a glycerin molecule. form a bond (compound) with the alkali and become a single soap molecule. The by-product of this reaction is glycerin. So three fat cells that were attached to a glycerin molecule are now joined in a long hydrocarbon chain with an alkali head.
We know this is a lot to take in and quite hard to visualise, which is why we've created a handy diagram below so you can see what we mean.
If you were to break down a molecule of soap you would have a fatty acid (hydrocarbon chain) which would be the tail, attached to an alkali head. You would also have a glycerin molecule completely separate in the solution.
This glycerin is one of the key ingredients in a natural soap as it moisturises the skin and keeps it soft, smooth and supple.
One of the key ways to determine whether your soap is a true soap or a synthetic surfactant “soap” is true soap will form a scum on your bath. This soap scum which is easily cleaned is where the fatty acids in the soap have reacted with minerals within the water. Most commonly these minerals are calcium and magnesium.
These are two of the key components within the water in high proportions which make water ‘hard’.
What are synthetic surfactants?
So we've given you an introduction to surfactants and told you about surfactants that are formed in natural soaps. But there are other surfactants out there as well which can be made synthetically. So what are synthetic surfactants?
Synthetic surfactants are surfactants that have been manufactured to have the characteristics of a surfactant. This involves combining individual elements together to form the surfactant. This will usually involve combining together a hydrocarbon chain, an acid and an alkali to form a surfactant.
The initial part widely available is the hydrocarbon (oil loving) part of the surfactant. Hydrocarbons are widely available as they are a by-product of the petrochemical and palm oil processing industries.
The middle part of the surfactant, which in a natural soap is carboxylic acid, pH 2-3 is now replaced with another acid, usually sulphuric acid pH 1, which is slightly stronger on the pH scale.
Once these two components have been fully bonded, the solution can now be reacted with a similar alkali to natural soap to produce a synthetic surfactant.
These manufactured surfactants are similar to an extent to a natural soap; however, they do have a couple of differences.
Firstly they do not contain glycerin, or produce it as a by-product, and this is a key component of why natural soap is so moisturising. After the soap has removed the dirt and bacteria from your skin, the glycerin is left behind on your skin to form a moisturising barrier.
Secondly, they do not react with hard water and tend to produce foam easily in hard water areas. These are the two main differences between natural surfactants and synthetic surfactants.
Unlike true soap, which has been made through the process of saponification, synthetic detergent soaps are not allowed to be called ‘soap’ as they have not gone through this process.
Instead these bars are usually marketed as things like ‘beauty bars’ or will just have a brand name on them.
What's best for my skin?
The best soap for your skin is a natural soap.
It is gentle and kind to the skin, contains only naturally occurring ingredients, and also moisturises after use. Whereas using a surfactant based soap bar can leave your skin dry and possible cause eczema or other dry skin conditions.
To conclude, soap is definitely a surfactant as it breaks down the dirt, oil and grease on skin easily.
Synthetic surfactants, such as those included in laundry powder, washing up liquid and liquid based “soaps”, are also surfactants, but due to their nature they are harsher and detrimental for skin due to the lack of moisturising glycerin made within them.
They both have their place in this world. I would recommend using synthetic surfactants for ease of cleaning clothes, dishes (use gloves), and other household cleaning tasks.
But for your skin I would definitely recommend using a natural soap, which will moisturise your skin after it has been cleaned. Your skin will definitely thank you for it.
I hope you have enjoyed this article and found it informative. If you would like to read more about the wonderful world of soap then click over to our blog where you can find many more informative articles.
You can also purchase natural glycerin rich soaps from our online shop.
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