j. Soc. Cosmet. Chem., 31,223-236 (September/October 1980) The lathering potential of surfactants--a simplified approach to measurement j. ROGER HART and MARK T. DEGEORGE, Organic Chemicals Division, lV. R. Grace & Co., Nashua, NH 03061. Received December 3, 1979. Presented at the Society of Cosmetic Chemists' Annual Scientific Meeting, December 6-7, 1979, New York, N.Y. Synopsis Simple FOAM HEIGHT MEASUREMENTS have commonly been used to compare shampoo ingredients and formulations. Usually run at high dilution under relatively static conditions, foam measurements often disagree with actual use experience. A rapid, simple method for the estimation of the LATHERING PROPERTIES OF SURFACTANTS, their mixtures, and finished formulations is described. The phenomenon of lather is defined and contrasted with simple foaming. Higher surfactant concentrations (ca. 1-2% active) and dynamic conditions are employed to produce volumes of lather whose flow properties are measured and compared. The lathering properties of sodium, ammonium and -triethanolamine lauryl sulfates sodium laureth(3)sulfate sodium c•-olefin sulfonate sodium trideceth(7)carboxylate dioctyl sodium sulfosuccinate disodium monococamido-MIPA-sulfosuccinate sodium acyl (cocoyl, lauroyl and myristoyl) sarcosinates ammonium nonoxynol-4-sulfate and amphoterics 2 and 6 are examined. The effects of the addition of fatty alkanolamides, sarcosinates, and betaines on the lather of several commonly used anionic surfactants are also noted. Lathering in the presence of a synthetic sebum loading is also described. INTRODUCTION The ability of shampoos and shampoo ingredients to form close, dense lathers is of great concern to the cosmetic chemist. This heightened interest springs from the fact that the consumers' aesthetic requirement for a rich lather, especially on oily hair, is so well known and often voiced. Therefore, the cosmetic chemist must formulate for performance, i.e., cleansing, conditioning, on the one hand while also providing the aesthetic qualities, i.e., lather, fragrance, etc. Of all the parameters the cosmetic chemist is called upon to measure, one of the most difficult to determine with simple, yet objective means, is the comparison of the lathering ability of various ingredients and formulations. This is complicated by the confusion and ambiguity surrounding the use and meaning of the terms used to describe this phenomenon. When discussing the ability of surface active agents to form liquid-air mixtures, it is helpful and, indeed, essential to differentiate between the two terms, lather and foam. 223

224 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS DEFINITIONS The term, foam, is a broad, generic term which includes the entire range from a dense, creamy shave cream-type to a wispy, large cell, loose, open network of fragile, interconnected bubbles. Lather, on the other hand, is generally thought of as a close packed, dense foam which exhibits viscoelastic flow properties and a finite, weight-supporting mechanical strength. Also associated with this phenomenon is the optical property of sheen and the tactile properties of lubricity and slip. g•/hile the quantification of foaming t•er se is of some general interest to the cosmetic chemist, it is the determination and optimization of lather that is of principal concern. Often, however, the foaming properties of surfactants and shampoos are relied upon because of the ease, simplicity and reproducability of foam measurements such as the Ross-Miles test. Lathering determinations have been proposed and used but often lack simplicity and/or reproducibility. EXPERIMENTAL METHOD Our work on incorporating quaternary ammonium compounds into anionic shampoo formulations utilizing sarcosinate surfactants led us to develop a simple method for examining the lathering properties of these mixtures. During our initial investigation, we examined several methods which are described in the literature. Of particular interest were procedures which were simple and allowed reasonably reproducible comparisons of lathering properties. Following the lead of mussman and Lennon (1), we attempted to correlate the sinking times of various solid objects through the volume of lather obtained in a kitchen food blender. In our hands, we found sinking times to vary several hundred per cent on identical samples. We also examined the method proposed by Moldovanyi and Hungerbuhler (2) which consists of introducing air into the solution at constant rate and determining the volume and density of the generated foam for various time intervals. Again, we were unable to obtain reasonably consistent results with a standard test solution. Volumes and weights of generated foams varied seventy per cent or more. Little improvement and simplification in the estimation of lathering ability has been reported since Neu (3) published his work in 1960. Working with active surfactant concentrations of 1.5-2.0%, this method was intended to generate and measure lathers comparable to actual shampoo lathers. This technique utilized a kitchen food mixer which allows maximum generation and expansion of lather. The shearing effect of the beaters simulates the high surface area and high shear rates produced during the actual lathering of the hair. This highly dynamic action was found to produce lather results far closer to those obtained in practice than do more static methods such as the cylinder shake test, Ross-Miles test or use of an oscillating perforated disc in a cylinder of surfactant solution. While no simple method of lather estimation can adequately simulate the actual action of lathering on the hair, we have developed a rapid, simple, inexpensive and