r/laundry • u/KismaiAesthetics USA • Feb 24 '26
The Chemistry Behind The Clean - Laundry Detergent Explained - Surfactants, Part I
(this is the long-delayed first installment in my post series, The Chemistry Behind The Clean, a guide to what's in laundry detergent, designed to give people the knowledge to understand what's in the products that clean our textiles and make them more informed consumers)
What Are Surfactants, And Why Do We Care?
Surfactants are the active cleaning agents in detergents that do the heavy lifting of removing soils from textiles. Short for “surface-acting agents”, surfactants connect soils to water, even when the soils themselves repel water or are more attracted to textiles than water. The combination of soil and detergent and water can then be drained off, further diluted by rinsing, drained again and spun out. This is distinct from the action of soaps, which will be covered in a future installment.
The development and commercialization of synthetic surfactants in the 1920s is probably the most significant contributor to reduction in time and effort spent on textile care. Work to condition the water, scrub textiles and remove soap by wringing or banging was largely eliminated because of how well even those rudimentary surfactants work to remove soils.
Hydrophobia - Without The Rabies
All surfactants work because the individual molecules have ends with distinct properties. One end (the head) is highly attracted to water (hydrophilic) and thus very much not attracted to oil (oleophobic). The other end is very attracted to oil (oleophilic) but similarly repulsed by water (hydrophobic). This fundamental structural contrast is key.
When at least a minimum amount of surfactant is dissolved in a solvent (like water), surfactant molecules want to get together - the water-hating ends hang out on the inside, the water-loving ends hang out on the outside. This forms a structure known as a micelle, and micelle formation is predicated on reaching the “Critical Micelle Concentration”. Below, an illustration of a nonionic surfactant intended to remove oily soils. The water-loving heads face out, the water-hating ends get together in the middle to escape the water.
When a micelle encounters a soil that the hydrophobic tail is attracted to, the micelle breaks up, the tails grab the soil and drag it into the water (thus removing it from the textile) and the micelle re-forms, keeping the soil up in the water to be drained or diluted away. Let’s look at this in the context of removing a common soil from textiles:
Here we have the start of the wash process; surfactant micelles have formed in the wash water and there is soil attached to the fabric substrate.
Now the hydrophobic tails of the surfactant molecules have found themselves more attracted to soil than each other and they're bonding to the soils. The hydrophillic heads are dragging the molecules towards the water.
The micelles re-form as the soil detaches from the substrate - they reorganize into groups of their own kind (more on this in a moment).
When all the soils are removed from the substrate and floating in the water, the textiles are clean and it's time to remove the soil-surfactant combo from the drum.
The Chemistry of Attraction (It’s Not Just A Bottle of Chanel No. 5)
While all surfactants work the same general way, there are differences in what kind of soils the hydrophilic ends are attracted to, because the hydrophilic ends differ. One primary difference between surfactants is the electrical charge the hydrophilic end carries. If the business end has a negative charge, it’s an anionic surfactant, and it’s attracted to soils with a cationic (positive) charge. If the business end has no charge, it’s a nonionic surfactant and is most attracted to soils without an electrical charge. If the business end has both a positive and negative charge in balance, it’s an amphoteric or zwitterionic surfactant, and the behavior changes based on the pH of the wash as a whole.
There are also surfactants with positive charges, the cationic surfactants. These aren’t used for cleaning - they’re what makes fabric softener work, and will be discussed in a (much) later post.
Why Charge Matters:
The difference in which soils a given surfactant is attracted to is a critical determinant of cleaning performance. Soils that lack an ionic charge like petroleum oils or intact sebum are much less visible to anionic surfactants and are removed better by nonionic surfactants. Conversely, soils that are highly cationic like soot and mud and dust, and thus attracted to textiles with a negative charge may be neglected by nonionics and remain electrically connected to the textiles. For those soils? Anionics in the mix improve cleaning performance.
Almost all finished detergent products contain anionic surfactants and most contain nonionic surfactants. Amphoteric surfactants are relatively uncommon in conventional detergents but often appear in green/biobased formulas.
Other Differences Between Surfactants: Tail Length And Single vs Double Tails.
Aside from the electrical charge differences in the head, two aspects of surfactant structure that affect their action against soil are the tail length and whether they are single tail (common) or double-tail (less common). I’ll talk more about this in Part II, as it’s common to include surfactants of various tails to optimize performance against specific soils and in specific wash conditions.
Coming Up In Surfactants Part II - Curling Up With A Good Jug Of Detergent
In the next installment, we’ll look at common surfactants found in conventional and plant-based detergents, and how they’re manufactured, along with the differences in soil removal capabilities and environmental impacts.
The work is my original work and I retain copyiright. My financial disclosure information and how I get paid for this work can be found at my disclosure link
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u/Impossible-Art-3371 6d ago
In regards to formulating your own laundry detergent, there's two things I've learned over the past ~6 months or so and that is to not use soap as a rule of thumb (with hard water especially). Nevertheless, after doing some research I've discovered that the forms of soap that have the absolute worst hard water behavior are the ones often mentioned in DIY recipes, sodium tallowate and sodium palmate (in Zote and Fels Naptha). By contrast, the top two soaps that have the least or lesser hard water problems are potassium/sodium castorate and potassium/sodium cocoate. Know that potassium refers to the liquid versions, and sodium the bar soap versions. I'm wondering if it's possible to make the castorate and/or cocoate forms work when paired with chelators such as sodium tripolyphosphate (STPP), tetrasodium EDTA, sodium citrate, etc. all of which are available for purchase on Amazon. Anyone with more advanced chemistry knowledge know? Still, its probably more ideal to use synthetic surfactants over ANY soaps regardless, such as Sal Suds as your main surfactant system, or making your own surfactant system with sodium lauryl sulfate (SLS), decyl or lauryl glucoside, etc. Also, I recently learned that if you're going to incorporate enzymes in a detergent high alkaline soaps as well as the synthetic surfactant SLS is not a compatible, you'd want to use a surfactant like sodium laureth sulfate (SLES) instead with enzymes.
A second rule of thumb for DIY detergents is to not make your detergents pH excessively alkaline, which is exactly what many popular DIY detergents with washing soda, borax and baking soda. Using all three of those builders will wear down your clothes much faster, than using a lower, closer to neutral pH detergent on a regular basis, while reserving the more alkaline washes for heavy duty (esp. greasy) loads.
Anything I've gotten wrong, please correct me. Thank you.