Your favorite skin products likely contain ingredients like carrageenan, lecithin, and mono-and diglycerides – these emulsifiers help maintain oil-in-water emulsions to create creamy textures for skin products.
However, how do you select an emulsifier suitable for your formulation? In this article, we’ll look at various emulsifier types as well as their advantages and drawbacks.
Amphiphilic emulsifiers offer an effective, natural alternative to synthetic surfactants; these molecules feature parts that prefer sitting in both water and oil phases, meaning when an emulsion forms its amphiphilic molecules will arrange themselves so their hydrophobic ends sit in fat and their water-loving ends are in the water, creating a physical boundary to separate both phases from mixing together.
Amphiphilic emulsifiers are used in a wide variety of food and cosmetic products, from salad dressings and baked goods to chocolate. Furthermore, these natural-source emulsifiers like lecithin or mono and diglycerides have been recognized by the Food and Drug Administration (FDA). They’re considered safe for human consumption.
Picking an emulsifier can be a complex endeavor. Your choice should depend on formulation constraints and what product type you intend to create; for instance, selecting an emulsifier that can withstand low temperatures or can easily be rinsed off may be required depending on product specifications and design constraints. In addition, consider pH levels within your formula as well as viscosity needs when choosing your ideal emulsifier.
Numerous companies are turning to natural emulsifiers derived from plant sources like soy lecithin and carrageenan as eco-friendly food and cosmetic additives, including food and cosmetic. Studies have proven these natural emulsifiers are just as effective at stabilizing oil-in-water emulsions while decreasing overall product oil usage.
Consumer demand for natural, eco-friendly commercial products has resulted in increased research into natural alternatives to chemical surfactants such as chemical emulsifiers. Natural emulsifiers may be used as replacements for synthetic functional ingredients found in foods, detergents, and cosmetics; it is important to understand their working mechanisms as well as any limitations they might present; currently, available phospholipids and biosurfactants are two such examples of such natural emulsifiers on the market.
Anionic, cationic, and nonionic hydrophilic emulsifiers are among the most frequently employed ingredients, featuring both water-loving (hydrophilic) and fat-loving (lipophilic) properties that attract water, while simultaneously pulling oil molecules together with it and binding with water into micelles; tiny bubbles of oil suspended in liquid form which create an emulsion with creamier textures and greater viscosities than its initial version.
In order to select an emulsifier that best meets your recipe’s needs, take into account its HLB (hydrophilic-lipophilic balance) value. HLB measures how soluble surfactants are both in oil and water environments – lower values indicate greater oil solubility while those with higher values promote water-in-oil emulsions while higher HLB numbers encourage oil-in-water emulsions.
HLB serves only as an indicator and cannot fully capture all aspects of an emulsion’s stability; however, it can provide a starting point in search of an ideal formula.
Consideration should also be given when selecting an emulsifier’s zeta potential, which measures its stability. A higher value indicates stronger repulsive forces between oil and water molecules resulting in greater stability of an emulsion.
The Zeta potential of an emulsion depends on several factors, including the pH of water and the concentration/type of surfactant used to form it. An unstable state would typically fall below 30mV while 60mV and above is usually indicative of good stability.
An important consideration when selecting an emulsifier is compatibility with the ingredients in your recipe. It is vital that it mix smoothly with all other components of your emulsion; to make sure this happens successfully it’s important to conduct multiple tests on polished and grit blasted surfaces prior to production.
Vaerman conducted a study comparing six food-grade emulsifiers with HLB ranges between 3.4 to 8.0 on the physical stability of a casein-maltodextrin-soybean oil compound emulsion. Their use significantly enhanced centrifugal precipitation rate, emulsifying activity index, microrheological properties, zeta potential, average particle size, and Turbiscan stability index values.
Cosmetic products contain emulsions with two almost incommensurable phases. To stabilize such systems, chemists must select an emulsifier suitable for each of the oil and water components based on several criteria such as stability of the emulsion, amount of surfactants used, and ability to lower the surface tension between phases – not an easy feat!
Emulsifiers are amphiphilic molecules that facilitate the mixing of oily or waxy substances with water. They consist of two parts – a polar hydrophilic head and a non-polar hydrophobic tail; its non-polar tail burrows into the oil while leaving its polar head exposed to water, creating micelles – tiny particles floating in a solution that trap bits of oil – Mayonnaise is one such example of such an oil-in-water emulsion.
HLB values of surfactants are one of the key indicators in their classification as an emulsifier, serving as an index of how their proportion of hydrophilic and lipophilic moieties compare with each other; higher HLB values indicate greater solubility in water; high HLB values typically used with oil/water emulsions while those with lower values work better with w/o formulations.
While there are various methods for calculating HLB values, it should be remembered that these calculations ignore other crucial aspects that influence interfacial interactions, such as the temperature of oil and aqueous phase components and interactions among ingredients when choosing an emulsifier.
Cationic emulsifiers are frequently employed in oil-in-water emulsions due to their ability to lower surface tension and increase dispersed phase strength, while also stabilizing the aqueous phase in O/W emulsions. Furthermore, these emulsifiers tend to prefer operating in acidic environments and preferentially tolerate conditions where pH levels of the water phase remain acidic.
Cationic emulsifiers tend to irritate the skin, increasing the risk of sensitization. Furthermore, these products form lamellar gel networks which may not be as stable as traditional emulsions; so these should only be used sparingly and carefully.