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Topic Last Updated on 08-07-2024
HEAVEN-SENT CLEANLINESS
Soap can arguably be considered the most popular surfactant. Sodium or potassium salts of fatty acids make up the core of the cleansing agent, and they have a complex structure. The molecule of such acids is “bilateral”: one half repels water (hydrophobic), and the other is attracted to it (hydrophilic). When you soap up your hands, the hydrophobic parts of the molecules come into operation, moistening the grease. When we put our hands in water, the hydrophilic side comes into play — it attaches itself to the water and carries away the whole molecule, along with harmful substances and bacteria, into the sewer system. If you simply rinse your hands with water, the fatty particles and the contaminants they have accumulated will remain on your skin.
HOW DOES SOAP WORK?
The hydrophobic part of the molecule is active in all non-polar solvents, such as gasoline or oil, so soap is well-suited for the removal of such contaminants. It is interesting that surfactants can work only at the interface between two states: liquid-gas, liquid-solid, or two immiscible liquids. They look for boundaries between states, just like spies, and this is why substances that reduce surface tension are called surfactants, or “surface- active agents”. The surfactants have mastered an entire procedure for transit from the liquid solution to the state interface — adsorption, the essence of which lies in the accumulation of substances in the surface layer. Surfactant molecules are able to independently move to the interface of two substances.
If there are too many surfactants, more than the boundary can hold, the molecules gather into microscopic spherical droplets of micelles (from the Latin “micella,” meaning a small particle).
The micelle is a sphere of molecules with protruding hydrophilic ends and a diameter of a few nanometers.
Acquiring a micellar solution is simple: to make it, pour a thin stream of liquid soap into water until it becomes cloudy. Such a solution with microparticles of liquid soap, capable of wetting many surfaces, is called a colloidal solution. By the way, milk and blood also belong to the category of colloidal solutions.
Different Surfactants are Necessary
Ninety-nine percent of all surfactants are organic substances — alcohols, fatty acids, and their salts, as well as other compounds based on carbon and hydrogen. According to the stories of the ancient Roman writer Pliny the Elder, people were able to use such compounds as surfactants even before the common era. To do so, they mixed wood ash from beech with goat fat, and voila! The first soap was created. Later, alchemists thought up the idea of treating natural oils with sulfuric acid, and the French scientist Edmond Frémy prepared detergents from olive and almond oils in 1831.
In Germany in 1843, people added coconut oil to their cooking pots for soap. At first, though, the aromatic soap did not sell very well. The new product did not have the familiar unpleasant smell of rancid fat, which people had grown used to, so they thought the coconut soap to be low-quality.
Modern surfactants are divided into ionic and non-ionic. They are distinguished by their behavior in aqueous solutions; ionic surfactants become ions when dissolved. Both positive charge ions (cations) and negative charge (anions) can display surface activity. They are called cationic and anionic, respectively. Cationic surfactants are organic bases with salts, while anionic ones are organic acids with salts.
Amphoteric surfactants are the sort of “Dr. Jekkyl and Mr. Hyde” among ionic substances because they are able to manifest both as cationic in acidic solutions and as anionic substances in alkaline solutions. Non-ionic substances do not decompose into ions in water, but they dissolve perfectly due to the formation of a hydrogen bond between the H2O molecule and the functional group of surfactants. Such surfactants appeared relatively recently, in Germany in the 1930s, but they already hold a steady position in the world in terms of production volume, second only to anionic surfactants.
A DAILY CHEMICAL
SODIUM LAURYL SULFATE
White powder
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Sodium lauryl sulfate (SLS), or sodium dodecyl sulfate, is a surfactant in products like toothpaste, shampoo, shaving cream and bath foam.
In shampoo
Sodium lauryl sulfate is a surfactant, the molecule of which contains both a water-soluble and water-insoluble part. It attaches to grease or dirt and tends to dissolve in water. This substance also reduces the surface tension of water and forms bubbles.
In toothpaste
SLS in toothpaste acts as a foaming agent and irritates taste buds, dulling them and breaking down phospholipids that inhibit taste receptors. This makes orange juice taste more bitter after brushing, as SLS numbs taste buds, intensifying the bitter aftertaste.
Engine degreaser
Sodium lauryl sulfate is found in engine degreasers in higher concentrations than in shampoos. It’s also used in various industries as a leather softener, wool cleanser and floor cleaner.
Potential protection from sharks
Studies conducted in 2001 showed that sodium lauryl sulfate exhibits shark-repellant properties due to its hydrophobic nature. However, despite this potential application, the substance is not used as a primary means of protection against shark attacks. Semiochemicals, as well as defensive toxins of marine organisms, were proposed as alternative repellent agents.
