J. Soc. Cosmet. Chem., 25, 581-591 (November 1974) The Stabilization of Nonionic Aerosol Emulsions. Propellant Additives PAUL A. SANDERS, Ph.D.* Synopsis-Previous work had shown that certain nonionic POLYOXYETHYLENE (POE) FATTY ETHER-FATTY ALCOHOL COMPLEXES stabilized AEROSOL FOAMS, but not the EMULSIONS from which the foams were obtained. These complexes were pre- fo•xned in the aqueous phase prior to addition of the PROPELLANT. In this study, aerosol enmlsions containing the comp]exes were prepared differently. Fatty a]cohols were dissolved in the propellant, and the resulting solution was added to the aqueous sur- factant phase. This method formed the nonionic surfactant-fatty alcohol complex directly at the propellant-water interface during addition of the propel]ant. Adding fatty alcohols with the propellant increased emulsion STABILITY with three POE fatty ethers. Three other POE fatty ether-fatty alcohol complexes failed to stabilize emulsions regard]ess of how the alcohols were added. The failure of these complexes was attributed to their high water solubility. There was no apparent relationship between the properties of the nonionic aerosol emul- sions and those of the foams. Whether or not the surfactant-alcohol complex stabilized the aerosol emulsion had little effect upon fomn stability. INTRODUCTION Aerosol cosmetic and pharmaceutical foams have become increasingly pop- ular over the past decade. Commercial foam products include shaving lathers, skin moisturizers, colognes and perfumes, hair dressings, hair setting foams, body lotions, insect repellents, sunscreens, cleansing creams, depilatories, and medicated foams containing analgesics and antiseptics. Most aerosol foams are formulated as oil-in-water emulsions. The lique- fied propellant usually constitutes the maior portion of the dispersed phase. Most aerosol oil-in-water emulsions are formulated with anionic surfactants, such as the salts of the fatty acids. Adequate emulsion and foam stability can be achieved by designing the formulations so that molecular complexes are present. Molecular complexes are association compounds formed by the inter- action between surfactants and long chain polar compounds (1-5). The fact that these complexes increased both emulsion and foam stability (6) suggested a relationship between the properties of the anionic aerosol emulsions and their corresponding foams. * Freon Products Laboratory, E. I. du Pont de Nemours & Co., Inc., Wilmington, Del. 19898. 581

582 JOURNAL OF TItE SOCIETY OF COSMETIC CHEMISTS A study of anionic aerosol emulsions using photomicrographic techniques, coupled with a comparison of the physical properties of the emulsions and foams, showed that the most stable emulsions with the smallest droplet size produced the most stable foams (7, 8). From a practical standpoint, this em- phasized the importance of concentrating on the properties of the emulsions as well as the foams when formulating aerosol foam products. Nonionic surfaetants, such as the polyoxyethylene ethers, are not satisfac- tory as a class as emulsifying agents for aerosol emulsions. Out of eight eval- uated, only two were found to provide adequate aerosol emulsion and foam stability. Addition of fatty alcohols to aerosols formulated with the other six surfaetants caused a marked increase in foam stability, but in many instances emulsion stability was not improved (9). The poor emulsion stability of these systems limited the use of the polyoxyethylene fatty ether surfaetants in aero- sols. The fact that the POE fatty ether-fatty alcohol combinations increased foam stability but not emulsion stability indicated a lack of relationship be- twe:n emulsion and foam properties. This raised the question as to whether POE fatty ether-fatty alcohol combinations formed molecular complexes similar to the anionie surfaetant-long-ehain polar compound complexes stud- ied by Epstein et al. (9,) and Goddard and Kung (3-5). Although there are no published analytical data to prove the existence of POE fatty ether-fatty al- cohol complexes, there is indirect evidence. Thus, Beeher and Del Veeehio (10) determined film drainage transition temperatures for several polyoxyethy- lene lauryl ethers in the presence of lauryl and eetyl alcohols. They regarded their curves illustrating the change in surface viscosity with. temperature as being in the nature of melting point depression curves, possibly due to eom- pJex formation. Also, the stabilization of aerosol foams indicated that some type of interaction between the POE fatty ethers and fatty alcohols occurred (9)• In addition, many POE fatty ether-fatty alcohol combinations were high- ly pearleseent in the aqueous concentrate. The pearleseenee was attributed to liquid crystal formation (11). This indicated an association between the non- ionic surfaetants and fatty alcohols, i.e., complex formation. The failure of the nonionic pearleseent complexes to stabilize aerosol emul- sions could be due both to the stability of the complexes and the method used for their preparation (11). In previous work, the complexes were formed in the aqueous phase before the addition of propellant by melting the mixture of surfaetant and fatty alcohol and adding hot water. The aerosol propellant was pressure-loaded after the aqueous concentrate containing the pearleseent complex had cooled to room temperature. If the complexes had a high molecular weight, as suggested by their pearles- eenee, and were highly stable, they might not break up and collect at the pro- pellant-water interface after the propellant was added. The aerosol emulsion would then consist of a mixture of essentially unstabilized propellant drop-