2004 ANNUAL SCIENTIFIC SEMINAR EMULSIFIER SELECTION AND USE Mark Chandler Uniqema, New Castle, DE 401 The essence of making a stable emulsion is creating droplets and stabilizing them. Mechanical energy (mixing), thermal energy (heat), and chemical energy ( emulsifiers and stabilizers) are employed in various amounts to accomplish this humble task. The job of the creative cosmetic chemist is to use these tools to create the next great cream or lotion. The good cosmetic chemist has to think not only of stability of the product, but the aesthetics and performance of the product as well. Can the approach to stabilizing the emulsion help with these aspects as well? The cosmetic chemist generally thinks of emollients and actives/functional materials first when asked to design the next great cream or lotion. It is suggested that this habit be broken. With Marketing calling the shots, the selection of actives or functional materials will never leave its place of prominence, but the prominence of emulsion and emulsifier selection should rise higher than its current status. Armed with information on the particular active or functional material to be used and an idea of the needs and desires of the target market (Marketing WILL tell us that, right?), the cosmetic chemist can select the emulsion 'platform' that is right for the job. There are four primary stabilization mechanisms to choose from: 1) lOillC 2) steric 3) polymeric 4) liquid crystalline Ionic stabilization is the oldest method used. Soap-based emulsions have been produced for centuries and are still in use today. More modern anionic and cationic emulsifiers are finding their way into formulations. These emulsifiers build an ionic double-layer around emulsion droplets leading to electrical repulsion of the droplets. These emulsifiers tend to be efficient but have limitations in terms of pH, salt tolerance, and irritation potential. The mechanism that is most flexible and most widely used for making oil-in-water emulsions, steric stabilization, requires the most finesse in order to produce a stable, easily manufactured product. Such timesaving tools as the Hydrophile-Lipophile Balance System (filB), the Lin method of oil phase water solubilization determination, and Phase Inversion Temperature (PIT) have proven to be very useful in the formulation process, especially if steric stabilization is to be used as the primary stabilization mechanism. In many cases ionic and steric stabilization are used together. The use of polymeric materials as primary emulsion stabilizers has increased in the past few years. These stabilize by building 'zero shear viscosity' in the aqueous phase of an emulsion and have some interaction at the surface of emulsion droplets. Though

402 JOURNAL OF COSMETIC SCIENCE straightforward to formulate, these emulsions can be sensitive to extremes in formulation pH and salt content. The rheology and break characteristics of these emulsions can be far different than other emulsions - for better or worse. More often, water-soluble polymers are used to augment a primarily steric stabilized emulsion. Liquid crystalline phases are two dimensionally organized multilayers of lipophilic emulsifier. Most often used to build viscosity, stability, and pleasing rheology in steric stabilized systems, these phases can be used as the primary emulsion stabilization mechanism with excellent effects. If used as the primary emulsifier, these can stand the help of a small amount of polymer to assist stability. Even with the help, these emulsions are not very tolerant to excesses of salts or low pH. With a better understanding of the emulsion options available including their strengths and limitations, the cosmetic chemist can better serve their target market (and thus rise to fame and fortune.)