A SURFACTANT WHAT IS?
What is... A SURFACTANT?
Surfactants are arguably the most versatile of all molecules, as Jordan Petkov explains
Professor Jordan Petkov, Director Strategic Projects and External Research, Lonza Janus was the Greek god of gates and doors. He represented the middle ground between beginning and end, war and peace, barbarism and civilisation. What does that have to do with surfactants? Well, these are ‘middle ground’ products, which have found their way into ‘pacifying’ otherwise immiscible (incompatible) materials such as oil and water. The Greek link is even reflected in the word ‘surfactant’ – a composite from surface active agent – which is an ‘amphiphilic’ molecule that gets its name from αµφις, amphis: ‘both’; and φιλια, philia: ‘love’.
Nowadays surfactants are arguably the most versatile of all molecules, given their myriad applications.
The use of surfactants dates back to 2,800BC in Babylon, where a recipe for soap was found on a clay tablet. The soap molecules are long chains of fatty acids neutralised with some alkali base. Today we have at our disposal different types of surfactants – way too many to list here. They can, however, be split into four distinctive groups based on their hydrophilic heads (this is the part that likes water) and the hydrophobic part (most often hydrocarbon, with at least eight carbon atoms, figure 1A): • anionic, in which the hydrophilic/polar head is negatively charged, eg sulfates, soaps;
• cationic, in which the polar head is positively charged, eg quaternary ammonium salts;
• non-ionic, a molecule that has no charge, eg ethoxylated aliphatic alcohols;
• zwitterionic, which possesses both charges and is sensitive to the pH. These are one of the most expensive surfactants, due to their mildness to the human skin.
Surfactants, or at least those that are water- soluble, immediately shoot for the air-water interface when added to water. They protrude the hydrophobic chain in the air (oil is also preferred when oil and water are considered, figure 1B), and reduce the surface tension of the air-water interface. The surface tension would otherwise
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No bubbles will be stable without the introduction of surfactant molecules
prevent the foam formation if you simply tried generating foam with pure water.
No bubbles will be stable unless you introduce surfactant molecules. When it comes to cleaning oily stains, surfactants adsorb at the oil-water interface. This causes the roll-up of the oil due to the reduction of the interfacial tension between the water and the oil, so removing the stain from the fabric.
By their very nature, surfactant molecules form in bulk in highly complex structures such as spheres, cylinders and lamellae, in different conditions. These metamorphoses are driven by the attempt of the molecules to keep their hydrophobic parts away from the water once the air-water interface is saturated. To make things more complex, you can imagine the opposite situation when the surfactants are predominantly soluble in oil. The aggregates will be ‘hiding’ their polar heads from the oil and expose their hydrophobic chains by forming some hairy aggregates.
The irony with surfactants is that the better it is in cleaning, the less mild it usually is to the skin. As we understand more about how surfactants work, scientists have been able to create molecules that satisfy the requirements of today’s more knowledgeable consumers, who want natural products without any compromise on performance.
One family of such molecules is SYNETH – Lonza polyglyceryl esters, a great example of a molecule with 100% natural origin and versatility across many applications in personal care. The molecules are built of glycerol and fatty acids, all coming from vegetable oils. SYNETH provides the perfect balance between aesthetics, mildness and functionality, addressing consumer expectations regarding environmental concerns. Surfactants are our friends, often invisible, but they are here to stay and will serve us for years to come
Figure 1
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