CATIONIC SURFACE-ACTIVE AGENTS 229 Adsorptive Properties Many quaternary ammonium compounds are strongly adsorbed on solid surfaces. This property has been utilised in many fields ranging from the flotation of minerals to antistatic treatments of plastic goods. They are adsorbed particularly by proteins, notably keratin. This property is one of the most valuable in relation to cosmetic uses of quaternary ammonium compounds, particularly in hair preparations of all types. The most spectacular effect of the adsorption of quaternary ammonium compounds on the hair is to eliminate scroop from hair which has been washed with anionics, bleached, or permed the adsorbed film gives body to fine hair and yet softens coarse hair, is lubricant, and considerably reduces static. A recent paper on this subject is due to Mills, Ester and Henkin, • while earlier reviews of this application of quaternary ammonium compounds have been published by Hilfer. TM The adsorption on skin is of value also in the formulation of barrier creams. The extent to which any given quaternary is adsorbed is a function of the surface involved, the concentration of the solution, pH and temperature. With any one surface and constant conditions different quaternary ammon- ium compounds are adsorbed in differing degree. In general the maximum adsorption for cosmetic purposes is found with compounds containing a hydrophobic group comprising 16 to 22 carbon atoms. Dyestuff Fixation Direct dyes suffer from the disadvantage that they bleed in water the quaternary ammonium compounds prevent or reduce this effect. With these and other dyes, quaternary ammonium compounds may also act as levellers and restrainers, and as a result have come to be fairly widely used in colour rinses, particularly those of the shampoo type. Since actual chemical combination between the dye and the quaternary ammonium compound may occur, it is frequently found that the quaternary ammonium causes a change of shade which must be anticipated when formulating. The alkyl pyridinium salts appear to be the most popular for this applica• tion, but several other quaternary ammonium compounds are also used. L'Oreal TM have claimed the preparation of creams with dye content which contain both cationic and anionic surface-active agents. ANALYSIS It is clear from the foregoing discussion that comparatively small variations in either structure or purity of a quaternary ammonium compound can result in large variations in properties. Unfortunately many commer- cially available quaternary ammonium compounds are supplied under rnisleading names and frequently without specification. Thus "lauryl

230 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS pyridinium chloride" may be either a pure Cx• derivative or, as with com- mercial grades of sodium lauryl sulphate, a mixture of homologues only part of which is Cx•. Likewise it is widely believed that cetnmide is synonymous with cetyltrimethylammonium bromide (see, e.g., cetrimide is not and has never been cetyltrimethylammonium bromide, but simply contained cetyltrimethylammonium bromide as one component, as in the case of a number of products described as "cetyltrimethylammonium bromide." Traditional methods of analysis cannot readily establish the composition or concentration of a quaternary ammonium compound, and new methods of analysis have had to be devised to resolve these difficulties.• •)UARTERNARY AMMONIUM COMPOUND FORMULATIONS Typical formulations based on quaternary ammonium compounds have been reviewed previously. TM The present discussion will therefore be limited to uses of major importance and in particular to current trends. / Bactericidal Use A number of products covering widely different consumer application's are now• available which utilise the bactericidal properties of quaternmy ammonium compounds. These include antiperspirants and deodorants, barrier creams, antiseptic creams, dandruff remedies, baby creams, lotions and powders, after-shave lotions, together with various pharmaceuticals such as cough syrups and lozenges, oral preparations of antibiotics, and, of course, antiseptic fluids. Of interest in view of the introduction of by-laws governing the conduct of hairdressing establishments is the appearance of a quaternary ammonium compound based disinfectant which has been designed especially for use in hairdressing saloons and b•auty parlours. •4,•5 The vast majority of the above type of products contain as active bacteri- cide either cetrimide, benzalkonium chloride or cetylpyridinium chloride. Permanent Waving and other Hair Treatments It has become widespread practice to use a quaternary ammonium compound preparation at one or another stage of permanent waving. The quaternary ammonium compound may be included with thioglycollate in waving lotions or creams, with the neutraliser, or used after the waving process as a conditioner or as a setting lotion. The last two types of product are more frequently used after normal shampooing. The addition of quaternary ammonium compounds to peroxide bleaches in salon practice is popular, and Hudnut •6 have recently claimed the prepara- tion of acid peroxide bleaches containing quaternary ammonium compounds. Shampoos based on, or containing minor proportions of quaternary