J. Soc. Cosmet. Chem., 21, 365-375 (May 27, 1970) Surfactant Location Required HLB* and TONG JOE LIN, Ph.D.* Presented September 9, 1969, Seminar, St. Louis, Mo. Synopsis--Previous studies indicate that the location of the surfactant at the time of emulsifi- cation plays a very important role in determining the physical properties of the EMULSIONS formed. In this investigation, the HLB required to form an O/W emulsion was studied as a function of the initial SURFACTANT LOCATION in the OIL AND AQUEOUS PHASES prior to emulsification. Placing the surfactant blend in the aqueous phase prior to emulsification generally re- sulted in an apparently lower value of required HLB than the same system prepared by ini~ tially dispersing the surfactant blend in the oil phase. The initial surfactant location also showed a marked effect on emulsion stability. In the systems studied, using the emulsifica- tion technique described, placing the surfactants in the oil phase produced more stable emul- sions than the same systems prepared by initially placing the surfactants in the aqueous phase. INTRODUCTION Since Griffin first introduced the HLB (hydrophile-lipophile bal- ance) concept in 1949, a considerable amount of work has been done by many investigators to develop further the methods of measurement, to extend its applications, and to find the theoretical significance of the con- cept (1-4). HLB values of surfactants were originally obtained by a laborious de- termination of emulsion stability. Although such a method is still used, a number of other techniques have been proposed in recent years. * Research work was conducted while the author was with Max Factor 8c Co., Hollywood, CaliL *Shen Hsiang Tang Chemical Works, 19 Fu Shin Road, Section 4, Talchung, Taiwan. 365

366 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Becher and Birkmeier (5), for example, suggested a gas chromatographic technique to determine the HLB of surfactants. Gorman and Hall found a correlation of the HLB values and the dielectric constants of the surfactants (6). Ross and coworkers reported a relationship between HLB and spreading coefficients (7, 8). From kinetic considerations, Davies found a relationship between the HLB of a surfactant and its solubilities in water and oil and suggested a method of calculating HLB values from the structural group numbers ot• the surfactants (9, 10). In a more recent work, Shinoda and Saito showed a possible relationship between HLB and phase inversion tem- perature of the surfactant (11). Although the HLB system has wide applications, perhaps the most valuable aspect of the HLB concept to a cosmetic chemist is its usefulness in selecting an effective surfactant system for emulsification. According to the concept, for a given oil and chemical type of surfactant, an emul- sion having an optimum stability can be prepared when the HLB of the surfactant or the surfactant mixture agrees with the "required HLB" value ot• the oil to be emulsified. The concept thus provides a means to reduce the number ot• trials required to arrive at the most effective sur- factant combination for the emulsification of an oil to form either a W/O or an O/W emulsion. To take advantage of this method, one would have to know, or be able to determine, the HLB value of each surfactant component and the "required HLB" value ot• the oil or oil blend. A relatively large amount of HLB data for surfactants is now available but only a small amount of data is known on the required HLB values of oils and waxes (12, 13). This is partly due to the difficulty in accurately determining the required HLB values. Although possible correlations between the required HLB and spreading coefficients, or between the required HLB and dielectric constants, have been suggested (6, 8), the present procedure for determining the required HLB values of the oils generally involves a trial emulsification method using a pair of surfactants with known HLB values. Indeed, compared to the information available on the HLB of sur- factants, data on the required HLB for oils have not been thoroughly ex- amined. Like the HLB values of surfactants, the required HLB of an oil mixture is generally regarded as a linear function ot• the required HLB values of the components. However, the work ot• Ohba suggested that this may not be exactly true in some systems (14, 15). Recently, Griffin