Emulsions are well-known systems within the pharmaceutical, biotechnology, and food industries for the properties that allow them to comprise numerous consumer products. Each of these products contains either a water-in-oil (w/o) or oil-in-water (o/w) emulsion. Regardless of the fact that both types are majorly made up of the same two compounds, each is distinct in its chemical properties, applications, and more; having an understanding of these differences will help you make a more informed selection for your own application.
Read below for 3 specific differences between w/o and o/w emulsions.
- Suspended vs. continuous phase
Perhaps the most basic, but also the most significant, 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. O/w emulsions are comprised of oil droplets suspended in an aqueous phase, while w/o emulsions are the opposite- water droplets suspended in a continuous oil phase. 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; as such, 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. And homogenized milk is simply formed from the dispersal of fat droplets in an aqueous layer. In contrast, w/o emulsions make up oil-based products like sunscreen and most makeup. Additionally, its milder nature and ability to leave the skin’s lipid bilayer intact makes the w/o emulsion an ideal base for dry/sensitive skin treatments.
- 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, whether w/o or o/w, 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. Polysorbate, sorbitan laurate, and cetearyl alcohol are just a few examples of emulsifiers that are compatible with o/w emulsions. In contrast, while w/o emulsions only require one emulsifier, there is a limited number to select from because the hydrophilic balance must be in a narrow range (3-6). Sorbitan stearate, lecithin, lanolin/lanolin alcohols, and glyceryl monooleate are some examples of viable w/o emulsifiers.
Which is a Better Fit for Your Application?
Your selection of either o/w or w/o emulsion will largely depend on the type of product you are making, which emulsifiers you have access to, and the equipment you have available. No matter which you choose, however, you will require a homogenizer to synthesize your emulsion. The homogenizer will shear fluid by forcing it through a restrictive valve, forming a high-quality emulsion. Pion offers BEE brand homogenizers that are both high-quality and reliable, and which can help your lab produce nano/micro emulsions, dispersions, and suspensions to be incorporated into your pharmaceutical cream.
