98 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 500 4OO 3OO 200 0 50 100 150 200 250 300 350 Distance [% of initial] .... before treatment -- after dycing aRer treatment -• aRcr 1st treatment + shampooing Figure 6. The effect of oxidative dyeing and treatment with 0.2% polyquaternium-11 (procedure A) on the combing curves of virgin, dark brown hair. polyquaternium-11 and 2% hydrogen peroxide was employed. For comparison, a com- mercial conditioning formula of a neutralizer including quaternium-52 was also used. Dyeing. Hair was dyed by employing a black shade of a conventional oxidative haircolor that did not contain conditioning agents. A dye lotion, after mixing with an equivolume amount of 20 volume hydrogen peroxide, was left on the hair for 30 minutes, followed by extensive rinsing with water and shampooing with 3% ammonium lauryl sulfate. RESULTS AND DISCUSSION The properties of hair surface can be affected by both chemical and physical modifica- tion. Reactive chemical treatments usually increase the hydrophilicity of hair because of dissolution of surface lipids, deposition of dyes, breakage of disulfide bonds, and keratin oxidation, which leads to the formation of hydrophilic groups. These changes in the chemical composition of hair surface result in an increase in fiber-to-fiber or fiber-comb adhesion, which is further reflected in higher combing forces, especially in the wet state. Physical modification of hair, through adsorption of conditioning agents such as cationic surfactants, polymers, or oils, is usually designed to alleviate the damaging effects of reactive chemical treatments by lowering the combing forces. In this work, two experimental protocols are employed to quantify the effect of modi- fying treatments on hair. Both employ treatment frames with two windows to produce

SPATIALLY RESOLVED COMBING ANALYSIS 99 2000 1500 lOOO 500 1st treatment 2nd treatment 3rd treatment 115o4-1•0 .......... 810-J-6• 10334-140 o Untreated After 1st After 3rd Hair Shnmp. Shnmp. After Dyeing After 2nd After 4th Shnmp. Shnmp. Figure 7. The combing work of dyed hair after consecutive treatments with polyquaternium- 11 followed by shampooings. spatially resolved modification of the fiber surface. In procedure A (Figure 2), a reactive composition, such as an oxidative dyeing or bleaching system, is applied through the windows, while the subsequent conditioning treatment is performed on the whole tress. After chemical modification, combing curves usually show two peaks corresponding to modified areas of hair. The height of the peaks can further decrease as a result of the application of a conditioning agent, and the extent of this reduction can be used as a measure of the efficacy of this treatment. It should be also noted that, in this case, the reference portion of the fibers is chemically unchanged, but modified with an adsorbed layer of a conditioning agent. In procedure B (Figure 3), the whole tress is chemically modified, and the conditioning treatment is applied through the windows. The combing curves, after the conditioning treatment, display two valleys, and their depth can be related to the efficacy of a conditioning agent. In this experiment, the combing curves allow for the assessment of a difference in friction resulting from adsorption of a con- ditioning agent on a substrate with uniform surface properties. The effectiveness of a conditioning agent on virgin hair can be assessed by applying the treatment through the windows (procedure B). The combing trace of hair treated in such a way reflects a difference in friction between untreated control sections of the fibers and those modified by an adsorbed polymer or surfactant. The relative lowering of the combing force in the treated areas indicates a conditioning effect. For chemically modi- fied hair, on the other hand, the conditioning effects can be studied by adopting both experimental protocols, procedures A or B.