THE EFFECT OE PHYSICAL FACTORS ON THE FORMATION OF COSMETIC EMULSIONS* ,, By G. L. STANKO, W. C. FIEDLER, and G. J. SPEP-.ANDI0• Purdue University School of Pharmacy, West Lafayelte, Ind"aria EMULSIONS, and particularly those of a cosmetic type and appearance, are becoming increasingly popular in the fields of cosmetics and medicine. The modern emulsion-type lotion is used, in one manner or another, by most women, and in many instances the practicing physician who wishes to prescribe, dermatological medication utilizes the emulsified lotion as a vehicle because it presents topical medication in a most attractive form. Certainly we all know that cosmetics are, without question, th'e "eli. re" of pharmaceutical preparations. Probably the least understood area of cosmetics is the field of emulsion technology, although paradoxically, cosmetic emulsions are the most popular type of lotions on the market. This is such a complex subject that I hesi- tate to enter into a discussion on the theoretical aspects of emulsions, par- ticularly when our main •interest is the practical application of good phar- macy to their preparation. The entire area of emulsions is still to be ex- plored, and in,my own experiences, the only positive thing about emul- sions that I have found is their degree of unpredictability. Since an emul- sion is a system containing normally immiscible substances, it can be ex- pected to present more problems in its manufacture and to have its prepa- ration more easily affected by minor factors than other types of cosmetic preparations. One of the most important problems the cosmetic manufac- turer faces is that of stability and shelf life of his products since, more often than not he must supply and ship his merchandise to different cli- mates and subject it to many unfavorable conditions, both in transport and in storage. From the standpoint ' of the consumer, there are perhaps three properties of emulsified lotions which are most important: viscosity or thickness, greasiness, and stickiness. While these properties can be controlled to a great extent by proper formulation, they can also be affected by the man- ner in which the product is made and of these factors, viscosity may ap- * Presented at the December 10, 1953, Meeting, New York City.

40 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS preciably influence the stability of the completed emulsion. With this in mind, it was decided to study the small and often overlooked variations in techniques used in lotion manufacture and to try and establish with a degree of certainty the best way of preparing cosmetic emulsions. It is no secret that the best way to establish uniformity of products is to eliminate all variables in their manufacture, and considering the many possible variable factors existing in emulsion production at least ten chief factors which may affect the final product with respect to its physical prop- erties are found: the purity of ingredients, the method of mixing (includ- ing the speed of stirring, duration of stirring, type mixer used, and order of mixing), the temperature of the two phases of the time of emulsi- fication, the types of emulsifiers used, the type of emulsion formed, the ratio of the internal to the external phase, the amount of entrapped air, and the size of the batch made. Obviously, to study all of these variables on any one formula would en- tail years of experimentation, and even then any results would have to be confined to the particular type of emulsion studied. Our investigations were conducted with a simple formula containing mineral oil as the dis- persed phase and using a non-ionic emulsifier. The formula was made as simple as possible and was developed for this particular experiment. It was not intended to produce an ideal emulsion because we wanted to be able to detect and measure changes in the product, either as improvements or as degradations as they were evidenced by altering some of the previously mentioned factors. The formula does produce an average o/w emulsion which has cosmetic possibilities. A stearic acid emulsion was first consid- ered, but was rejected as a test emulsion because the chief objective was to study physical factors only without the introduction of variables due to chemical reaction in forming a soap in the emulsion. The formula for the emulsion used in all tests is as follows: Heavy Mineral Oil ..... Lanolin Anhydrous .... Cetyl Alcohol ......... 35.0% 1.0% 1.0% Span 80 ............. 2.1% Tween 80 ........... 4.9% Distilled Water ...... 56.0% The specific factors studied were: the order of mixing the two phases, the temperature at the time of emulsification, and variations in the speed of stirring. These objectives were sought: (1) to determine whether the oily phase should be added to the aqueous phase or vice versa, or whether all ingredients could be put together at once and emulsified (2) to determine whether continuous stirring or intermittent stirring produces the more stable emulsion and (3) to determine the effect on stability of an emulsion by emulsifying it hot against that of emulsifying it cold. A total of seven emulsions was prepared from the above formula, and each emulsion was made three times. In each instance, the finished products were allowed