SHAMPOO FORMULATION 357 ??: At acid pH's, however, the "scroop" is more pronounced although not as fully developed as in the case of al- kyl aryl sulfonates under comparable conditions. The quaternary ammonium com- pounds produce somewhat different effects. On washing the hands with Altosept MB (alkyl imidazolinium chloride) or cetyl trimethyl ammo- nium bromide at pH 7, one becomes acutely aware of the ridges in the palms and fingers at alkaline pH's mild "scroop" is developed. In either case, after rinsing the hands hoogn, dilute acid will produce a very copi- ous suds and the "scroop" will al- most disappearsalmost, because a rinse of normal skin with dilute acid alone will cause a slight increase in friction. With non-ionic surface- active agents "scroop" effects are not marked although adsorption seems to occur to a limited extent as evidenced by slight sudsing after rinsing with water followed by a pH shift to the alkaline side. In short, the so-called drying or defatting effects of the synthetics may be explained in terms of adsorp- tion phenomenon. Fortunately, the adsorption of surface-active ions by proteins has attracted the consider- able attention of textile technolo- gists and biochemists. Work in this field has recently been reviewed by Putnam (2), Valko (3), and Harris (4). Complex formation between surhce-active ions and proteins is generally explained in terms of what is called "specific or intrinsic a•n- ity" and electrostatic forces. At its isoelectric point a protein is consid- ered electrically neutral. At pH's below its isoelectric point, the pro- tein becomes positively charged and cationic in nature under these conditions it combines with nega- tively charged colloids in which class are the anionic surface-active agents. At pH's above its isoelectric point the protein becomes nega- tively charged and anionic in char- acter under these conditions the protein will combine with positively charged colloids in which class are the cationic surface-active agents. The extent of protein surface-active ion complex formation is determined by hydrogen ion concentration and by electrolyte concentration. Ac- tually, however, solid proteins do adsorb anions at alkaline pH's and cations at acid pH's this is "ex- plained" in terms of intrinsic af- finity of the surface-active ion for the protein. Neville and Jeanson (5) in 1933 described the adsorption of lauryl sulfate and also Igepon T by wool at pH 1 the wool adsorbed 25 to 40 per cent of its weight of surface-ac- tive anion from a 0.5 per cent solu- tion. As the pH increased the ad- sorption decreased, although even above the isoelectric point of the wool adsorption is 2 to 3 per cent. Steinhardt, Fugitt, and Harris (6) investigated the adsorption of vari- ous anions by wool over the pH range of 1 to 6. While maximum adsorption of dodecyl sulfonic acid was approximately 25 per cent at pH 2, at pH 6 100 gm. of wool would still adsorb 1.2 gin. of anion. It was

358 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS also determined that complex forma- tion was reversible, washing the protein with water resulting in the removal of the anion. Steinhardt also concluded from these and other experiments (7) that the at•nity of anions for protein increased with molecular weight. Aicken (8) stud- ied the adsorption of primary and secondary alcohol sulfates (molecu- lar weight about 280) by wool. Ad- sorption was found to increase with increasing acidity to a maximum comparable to the acid binding ca- pacity of the woolmabout 80 to 100 milliequivalents per 100 gin. of wool. At neutral pH's per cent adsorption increased with increasing concentra- tion of the solution and was also en- hanced by the addition of electro- lyte. Attempts to desorb the alco- hol sulfate by soaking in water for 48 hours proved unsuccessful, in marked contrast to Steinhardt's re- suits. Finally, reference might be made to the work of King (9) and Neville and Harris (10). The latter confirmed earlier work that wool im- mersed in neutral soap solution ad- sorbs sodium ions (cations) faster than it does fatty acid this was evidenced by a rapid drop in pH of the soap solution. King earlier had analyzed soap solutions in which wool was immersed and had found tl•at sodium ions were adsorbed preferentially and that adsorption of oleate ions or oleic acid increased as the concentration of the solution decreased. This behavior is in marked contrast to the behavior of the highly dissociated neutral .syn- thetic surface-active agents. The evidence would indicate, therefore, that conditioned as we are to the use of soap, the normal feel of skin is simply that produced by high sodium ion concentration and fatty acid adsorption on the skin surface. The truth, as some one said, is rarely pure and never simple the data just reviewed must be consid- ered critically. These studies were all made under conditions approach- ing equilibrium and with relatively dilute solutions. Equilibrium con- ditions are possibly not attained in the short shampooing operation and dilute solutions are obtained only during rinsing. The 'variations in complexity of detergent solutions as a function of concentration are not yet fully appreciated there is still considerable argument as to whether protein adsorbs large miceliar aggre- gates, surface-active ions, or mole- cules. The viewpoint just discussed ap- pears to be, however, of some value in explaining and perhaps indicating the possibility of attacking some troublesome shampoo problems. (1) The rinsing properties of synthetics are undoubtedly affected by their adsorption properties. Anionic agents should rinse better at slightly alkaline pH's cationics should rinse better at slightly acid pH's. (2) Harshening of the hair, unman- ageability, and di•culty in combing after shampooing may very well be the result of increases in friction such as that noted as the result of adsorption of surface-active ions on the'skin adjustment of pH should overcome these di•culties. (3)