In contrast, emulsifiers with HLB values less than 10 are more hydrophobic and therefore better suited for w/o emulsions.įurthermore, different oils have different HLB requirements. Emulsifiers with HLB values greater than 10 are more hydrophilic and thus better at stabilizing o/w emulsions. The HLB scale ranges from 0 to 20, with 10 corresponding to an emulsifier that is equally attracted to water and oil. If the balance is tipped in either direction, the emulsifier may lose contact with the phase to which it is less attracted, causing the emulsion to break down.ĭifferent emulsifiers have different HLB values, which can predict their ability to stabilize various kinds of emulsions (Fig. In an ideal emulsion, the emulsifier is equally attracted to the water phase and the oil phase. How do product formulators choose which emulsifier to use for a particular emulsion? Calculating the hydrophilic-lipophilic balance (HLB) of an emulsifier or combination of emulsifiers can help. Non-ionic emulsifiers can be used alone or in combination with charged emulsifiers to increase emulsion stability. The type of emulsifier used depends on the application, with cationic emulsifiers typically used in low-to-neutral pH solutions and anionic emulsifiers in alkaline solutions. These polar head groups clash and tangle with head groups on other water droplets, sterically hindering the droplets from coming together. Non-ionic emulsifiers tend to have large, bulky head groups that point away from the oil droplet. When charged emulsifiers coat droplets in an o/w emulsion, the positive or negative charges on the outside of the oil droplets electrostatically repel each other, helping to keep the droplets separated. In this way, emulsifiers lower the interfacial tension between the oil and water phases, stabilizing the droplets and preventing them from coalescing.Įmulsifiers can be cationic (positively charged polar head group), anionic (negatively charged head group), or non-ionic (uncharged head group).
For a w/o emulsion, the emulsifier’s orientation is reversed: nonpolar tails extend outward into the oil phase, while polar head groups point into the water droplet. When added to an o/w emulsion, emulsifiers surround the oil droplet with their nonpolar tails extending into the oil, and their polar head groups facing the water (Fig.
Therefore, emulsifiers are attracted to both polar and nonpolar compounds. A type of surfactant (see Sidebar), emulsifiers contain both a hydrophilic (water-loving, or polar) head group and a hydrophobic (oil-loving, or nonpolar) tail. Today, a wide variety of nature-based and synthetic emulsifiers are available for the diverse fields that benefit from them, including food, nutraceuticals, home and personal care, biofuel, environmental cleanup, and industrial lubricant applications.Įmulsifiers work by forming physical barriers that keep droplets from coalescing. For centuries, cooks have added natural emulsifiers, such as egg yolk, mustard, or honey, to help prevent this separation. However, in the absence of emulsifiers, this unstable emulsion breaks down within minutes, and the oil forms a layer on top of the vinegar. In both cases, emulsifiers are needed to prevent the suspended droplets from coalescing and breaking the emulsion.Īnybody who has made a simple oil-and-vinegar salad dressing knows that, with enough shaking or whisking, one can make a temporary emulsion. In contrast, margarine is a w/o emulsion containing droplets of water or skim milk in a blend of vegetable oils and fat. Milk is an example of an o/w emulsion, in which the fat phase or cream forms tiny droplets within the skim milk, or water phase. Simple emulsions are either oil suspended in an aqueous phase (o/w), or water suspended in oil (w/o). These examples represent emulsions, which are stable mixtures of tiny droplets of one immiscible fluid within another, made possible by chemicals called emulsifiers. The immiscibility of oil and water has inspired the proverb “Oil and water don’t mix” and other expressions that reflect the general incompatibility of two entities, such as “My coworker and I are like oil and water.” Yet within our homes are numerous examples of products in which oil and water do mix: mayonnaise, milk, salad dressings, hand lotion, and hair conditioner, to name but a few. how emulsifiers are used in foods, nutraceuticals, personal and home care products, industrial lubricants, environmental technologies, biofuels, and other applications.how formulators choose which emulsifier to use for a particular emulsion.After reading this article, you will understand:
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