You’ve no doubt heard the phrase “Oil and water don’t mix.” It’s basically a way of saying certain items or people do not go well together. However, oil and water can mix with the right ingredients – specifically, emulsifiers. Emulsifiers prevent oil and water from separating by establishing a barrier that protects the droplets.
When oil and water are mixed powerfully, they form either oil-in-water (o/w) or water-in-oil (w/o) emulsions. In o/w emulsions, oil is dispersed in a continuous water phase, while in w/o emulsions, water droplets are dispersed in oil. The result of an emulsion of oil and water mix is depended on the volume fraction of both phases and the kind of emulsifier utilized. You can actually tell the difference between the two by measuring the electrical conductivity of the emulsion. If there is no conductivity, it’s an w/o emulsion.
Both o/w and w/o emulsions have unique applications and chemical properties, and you can better choose the type you want to use if you know more about these differences. In this blog, we’ll provide some characteristics of o/w and w/o emulsions and describe some of the differences between the two.
Used in moisturizing products and food products such as milk, mayonnaise and vinaigrette, o/w emulsions contain a low oil concentration. They are mixable with water, non-greasy, non-occlusive and will absorb water. The dispersion medium in these emulsions is water; o/w emulsifiers keep oil drops packed in water.
These emulsions are utilized in products including butter, margarine, cold cream and cod liver oil and are especially useful in products designed for dry or sensitive skin. Common w/o emulsifiers are sorbitan stearate, polyglyceryl oleate, lecithin, sorbitan monooleate and lanolin. Sometimes referred to as an inverse emulsion, w/o emulsions mix more easily with oils and have a high oil concentration. Producing w/o emulsions is more difficult than developing their o/w emulsions.
Following are three additional differences between o/w and w/o emulsions:
Suspended vs. continuous phase
The biggest difference between o/w and w/o emulsions is which phase is suspended and which is continuous. Oil and water are normally immiscible, but with proper mixing and stability agents, a permanent mixture, or emulsion, can be achieved. Smaller droplet sizes will enhance the effectiveness of either system; this may translate to increased bioavailability in pharmaceutical products or extended shelf life in food/beverage products.
Type of product that can be created
The chemical nature of an o/w emulsion is distinct from that of a w/o emulsion; each is most effectively used in different products. O/w emulsions are the basis of water-based products; in the pharmaceutical industry, they can be found in creams like moisturizers and topical steroid products. In contrast, w/o emulsions make up oil-based products like sunscreen and most makeup.
How to achieve stability
Stability is key when considering an emulsion synthesis technique; without it, the two phases will separate, and the product will have lower function. All emulsions require an emulsifier to assist with stability. O/w emulsions typically require more than one emulsifier, and they can be acquired separately or in a pre-mixed cocktail. In contrast, while w/o emulsions only require one emulsifier, there is a limited number from which to select because the hydrophilic balance must be in a narrow range.
Emulsions, emulsifiers, homogenization and other terms can be confusing, but at BEE International, we can steer you in the right direction based on your specific business needs. Simply contact us to learn more!