Surfactants

Definition [: compounds that lower the surface tension of a liquid, the interfacial tension between two liquids, or that between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsifiers, foaming agents, and dispersants]

Nearly all detailing chemicals contain surfactants; car wash concentrate, abrasive polishes, wax, sealants, coating leather cleaners and protectors and the list goes on. One of their functions is they help to spread (spreadability) a product and they ‘wet ‘(wettability) the surface to help various chemicals permeate the surface and do what they are formulated to do.

Perhaps the most misunderstood and confusing components of cleaning chemicals are the actual detergents, or surfactants. Surfactants (short for surface-active agents) are molecules that contain a hydrophilic, or “water-loving” end, and a hydrophobic, or “water-fearing” end. The electrical charge on the water-loving end of the molecule distinguishes between the different types of surfactants.

Surfactants perform other important functions in cleaning, such as loosening, emulsifying (dispersing in water) and holding soil in suspension until it can be rinsed away. Surfactants can also provide alkalinity, which is useful in removing acidic soils. Surfactants are classified by their ionic (electrical charge) properties in water: anionic (negative charge), non-ionic (no charge), cationic (positive charge) and amphoteric (either positive or negative charge).

Many surfactants will adhere to a paint surface to enhance gloss or stop water spotting or because they see the paint protection product as rather similar in structure to the oils they like to bond with. Many products that contain surfactant will leave a film on the paint surface, which attracts water so masking any beading or sheeting.

Be cognizant that not all surfactants do the same thing, nor do they do it to the same degree. A surfactant is to all intents a ‘wetting agent’, different surfactants have different ability to wet surfaces. Beading and sheeting (hydrophobic and hydrophilic) are really just differences in hydrophobicity. A simplistic explanation of a surfactant is a clingy oil.

Soap is an anionic surfactant. Other anionic as well as non-ionic surfactants are the main ingredients in today's detergents. The chemistry of surfactants- soaps are water-soluble sodium or potassium salts of fatty acids. Soaps are made from fats and oils, or their fatty acids

Surfactants come in four different types: Anionic, non-ionic, cationic and amphoteric.

Once you understand the differences between these different surfactant types, as well as how to classify them by their names, choosing the right cleaning products should be a snap.

Anionic surfactants

Probably the most commonly used surfactants in carpet cleaning chemistry are anionic surfactants.

Anionic surfactants possess a negative charge on their hydrophilic end. This charge helps the surfactant molecules to interact with both the carpet fibres and soil particles, lifting and suspending soils in “bubble-like” arrangements called micelles.

Anionic surfactants possess other benefits that make them ideal for certain carpet applications. Generally, they make a lot of foam when agitated. Also, they tend to be flaky or powdery when dry, not sticky like other surfactants.

Anionic surfactants, therefore, are the most common type of surfactant found in low moisture carpet cleaners, like traditional shampoos and encapsulation products. However, these detergents tend to not be as good at emulsifying oily soils as some other detergent types. 

When reading the ingredients list on your cleaning products, you can identify anionic surfactants as those that have the following in their names:

·         Sodium

·         Ammonium

·         Magnesium

·         Sulphate

·         Sulfonate

·         Gluconate

(For example, sodium laurel sarcosinate, magnesium laurel sulphate, and sodium gluconate.)

Non-ionic surfactants

Non-ionic surfactants are also found in many cleaning products, including carpet products. Non-ionic have no charge on their hydrophilic end, which helps make them superior oily soil emulsifiers. Some non-ionic are high foamers (like anionic), while others do not generate much foam. Because of their lower foam profile and strong emulsifying potential, these surfactants are the preferred choice when formulating extraction cleaners and pre sprays.

However, unlike anionic surfactants, non-ionic are thick liquids or syrups that are sticky or “gooey” to the touch. When left in the carpet, non-ionic surfactants are the primary contributors to rapid resoiling.

Even with that being the case, their importance as cleaners outweighs this negative, and the cleaner or technician must take care to remove as much of the detergent residue as possible from the carpet in order to get the cleaning benefits of non-ionic without their negatives.

Non-ionic surfactants include:

·         Ethoxylates

·         Alkoxylates

·         Cocamide

Cationic surfactants

Cationic surfactants are less common in cleaners, and almost always absent from carpet products. Cationic have positively charged ends, which makes them ideal in antistatic formulas like fabric softeners and automobile “cheater waxes.” Also, cationic surfactants have antimicrobial characteristics, and they are found in hard-surface disinfectants and cleaners.

However, cationic surfactants have been shown to damage the mill-applied protectants on carpet, and are therefore strictly verboten in carpet products.

Formulas containing cationic surfactants cannot be mixed with those containing oppositely charged anionic surfactants. The molecules would interact with each other, producing a gooey mess that drops out of solution. When reading the ingredients list, look for the words “chloride” or “bromide” (as in alkylbenzene ammonium chloride) to identify cationics.

Amphoteric surfactants

Probably the least talked about surfactants are the amphoterics. These unique molecules possess both a positive and a negative charge on their hydrophilic end, giving them a net charge of zero.

Amphoteric surfactants have little utility on their own, but work extremely well in enhancing the cleaning effect of both anionic and non-ionic surfactants. They can serve as “coupling agents,” which hold the surfactants, solvents and inorganic salt components of a formula together. Amphoterics are usually named in some way to indicate that they are amphoterics, as in amphoterge. Other examples of amphoterics are betaines and amine oxides.

Non-emulsifying surfactant

The development of new surfactants has brought aqueous cleaning into a new generation. New technology aqueous cleaners clean by subverting the soil. A non-emulsifying surfactant is designed to have a higher affinity for the substrate than the soil does. The surfactant thus "lifts" the soil from the part or surface without chemically reacting with it. For example, a non-emulsifying cleaner works well in spray applications. If a settling tank and oil skimmer are added to the system, soils can be removed and the cleaning solution can be reused, sometimes indefinitely, without recontamination.

Colloid

A colloid, or colloidal dispersion, is a form of matter intermediate between a true solution (like salt dissolved in water) and a mixture or suspension (Italian salad dressing right after you shake it). Further research revealed that colloids have minute particles called micelles. When combined with water, micelles break water's surface tension (the property that keeps water droplets round), resulting in "super wet" water. That same action allows the micelles to penetrate grease, oil and related organic soils and to hold them in liquid suspension. In effect, the micelle cleaning action is unique and can only be related to the effect of an atomic explosion where random interaction of the particles loosens the soil.

Micelle

A Micelle is a surfactant that consists of long molecules with two very different types of ends. One end likes water, and is called hydrophilic, the other end likes oil and dislikes water, and is called hydrophobic. When these surfactants are placed in water, the hydrophobic ends attract each other, and repel water, and arrange themselves into a spherical structure with the hydrophobic ends inside the sphere, and the hydrophilic ends on the outer surface of the sphere. This sphere is called a micelle.

Surfactants in Detergents

A detergent is an effective cleaning product because it contains one or more surfactants. Because of their chemical makeup, the surfactants used in detergents can be engineered to perform well under a variety of conditions. Such surfactants are less sensitive than soap to the minerals (calcium carbonate (CaCO₃), magnesium hydroxide (Mg(OH)₂), and calcium sulphate (CaSO₄) in water and most will not form a film.

Detergent surfactants were developed in response to a shortage of animal and vegetable fats and oils during World War I and World War II. In addition, a substance that was resistant to hard water was needed to make cleaning more effective. At that time, petroleum was found to be a plentiful source for the manufacture of these surfactants. Today, detergent surfactants are made from a variety of petrochemicals (derived from petroleum) and/or oleo chemicals (derived from fats and oils).

Surfactants in Soap

Soaps were the earliest surfactants and are obtained from fats which are known as glycerides because they are esters formed by the trihydric alcohol, propane-1,2,3-triol (glycerol), with long chain carboxylic acids (fatty acids).  The glycerides are hydrolysed by heating with sodium hydroxide solution to form soaps, the sodium salts of the acids, and propane-1,2,3-triol.  The process is known as saponification.

A buffet of chemistry

With all these different types of surfactants, and with a seemingly infinite list of each type of surfactant, it is a wonder that formulators are able to choose the right detergent for the right application.

Experienced formulators have gotten their hands dirty working with many different types of detergents in an effort to make just the right blend of cleaning agents.

Any formulator worth his salt will be quick to tell you that not all surfactants are created equal, and that some cleaners are better than others, given the situation.

Relevant Articles

Basic Soap and Detergent Chemistry

I would like to think that these articles become an asset to anyone who is new to detailing and to professional’s alike, as well as industry experts who seek to advance their knowledge.

I hope the above article was informative. By having some understanding of the ‘What’ and ‘Why’ as well as the ‘How’ along with a little science to help you understand how the chemicals we use react, you can achieve the results you desire.

I would appreciate it if you would share this article as it helps other detailers further their knowledge.

Questions and/ or constructive comments are always appreciated.

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