JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS The pH of the system has a biõ influence on the properties of the cationic emulsifiers as at low pH values the cations are more strongly adsorbed than at higher values. The deõree of surface sensitivity of an emulsion can be increased by (a) using a less ethoxylated derivative, (b) usinõ a longer chain length derivative, and (c) reducing the pH of the system. THE USE OF CATIONIC SURFACE ACTIVE CHEMICALS Burton (17) has reported the spreading properties of a cationic emulsion formed with lanolin, cetyl alcohol, isopropyl myristate, and water (50%), with a quaternary ammonium compound as emulsifier. At 4.0% emulsi- fier, an o/w system was formed which did not invert on spreading or re- wettinõ. At 0.4% the emulsion inverted on application to skin and re- verted to o/w on rewettinõ, whilst at 0.04ø,/o emulsifier a w/o system resulted which did not change on application. The selective wetting of the materials of construction of the emulsifyinõ equipment have also shown to affect the type of emulsion produced. An emulsion system is quoted by Dvoretskaya (18) as giving an o/w emulsion using glass equipment whilst the use of a plastic aõitator produced a w/o emulsion. The lowering of the pH of an emulsion system usinõ a quaternary ammonium compound can be achieved by usinõ the fatty acid salt of the quaternary compound as reported by Hilfer (19). I R' N (CH8)8] + C1- + fatty acid -• Complex + I-IC1 The adsorption of a quaternary ammonium compound onto fibres can be used to improve the "feel" of a blanket, and their bactericidal properties can also be used. An interesting product has been developed for treatment of hospital blankets (20) based on an oil emulsion using a quaternary ammonium compound (a) as an emulsifier, (b) as a sensitizing agent to give deposition of oil onto fibre, and (c) as bactericide. This type of formulation could be of value to the cosmetic chemist formulating deodorant and antiperspirant preparations. The hydrophobic barrier of adsorbed quaternary can be utilized in hand and barrier creams as the quaternary ammonium compounds con- taining two long alkyl chains give water repellent films.

CATIONIC EMULSIFIERS IN COSMETICS 25 The reaction product of anionic and cationic surface active chemicals can also be of value, and a patent (21) refers to the use of such a compound as a water repellant carrier for therapeutically active substances. Cationic surface active chemicals exhibit a high degree of substantivity towards keratin and the beneficial effects of an adsorbed layer on hair has been claimed in several patents (11-13, 22) and mentioned elsewhere (23,24). Cationic chemicals have been used as solubilizing agents for certain dye- stuffs giving products having high substantivity and dye levelling proper- ties. Emulsions are often desirable for aerosol formulations, particularly those designed for cosmetic use. The results of a study of a wide range of surface active chemicals showed that all classes have members which give good emulsifying and foaming characteristics. Of the cationic materials investigated the difatty quaternaries, e.g. distearyl dimethyl ammonium chloride, gave results similar to an alcohol sulphate, a sodium sulpho- succinate di-ester and a sorbitan ester. The effect of various additives on the propellant water systems were also studied and it was found that the emulsions were very stable, and not sensitive to other ingredients likely to be found in cosmetic formulations. A polyethoxylated laurylamine having 5 tool of ethylene oxide was found by Lesshafft and De Kay (25) to give optimum release of mercuric oxide and iodine medicaments when used at 1% in place of sodium lauryl sulphate in the standard formulation in USPXIV. Increase in the surface active chemical concentration causes a decrease in release which empha- sizes the necessity to formulate to optimal levels as over-usage can annul the beneficial effects of these systems. Several papers and patents (26-30) refer to the use of cationic surface active agents in cosmetic products, and reference to them will indicate some further ways of making use of the properties of these interesting chemicals. (1) (2) (a) (4) (5) (6) (7) (S) (9) (10) REFERENCES Du Brow, P. L. Am. Perfumer Aromat. 72 95 (October 1958). Lawrence, C. A. Soap Perfumery Cosmetics 27 369 (1954). Hilfer, H. Drug Cosmetic Ind. 76 466 (1955). Addison, C. C. and Furmidge, C. G. L. J. Sci. Food Agr. 5 212 (1954). Shibe, W. J. and Hanson, D. H. Soap Chem. Specialties 39 83 (1964). Seyforth and Morgan, Am. Dyestuffs Reptr. 27 (19 September 1938). Griffin, W. C. J. Soc. Cosmetic Chemists 1 311 (1949). Griffin, W. C. ibid 5 249 (1954). Tamamushi and Tomaki, Proc. 2nd Intern. Congr. Surface Activity III 449 (1957). Lincoln, P. A. J. Soc. Cosmetic Chemists 8 222 (1957).