EFFECT OF ANTEISO-BRANCH MOIETY OF 18-MEA 513 it is hydrophobic because of the presence of 18-MEA. On the other hand, that of alkaline-color-treated weathered hair was around 66.3° ± 3.1°, which means it is more hydrophilic. The specifi c feature of the 18-MEA/SPDA complex was to confer a persistent hydrophobicity and low friction to the alkaline-color-treated weathered hair surface (14). This means that the alkaline-color-treated weathered hair treated with the 18-MEA/ SPDA complex could maintain its hydrophobicity and low friction even after one in- stance of shampooing with a plain shampoo. The contact angles of alkaline-color-treated weathered hair treated with 18-MEA/SPDA, 19-MEA/SPDA, and n-HEA/SPDA after one instance of shampooing with a plain shampoo are shown in Figure 2. The conditioner formulations were as follows: 2 wt% SPDA 0.5 wt% benzyl alcohol 3.0 wt% stearyl alcohol 1 wt% fatty acid 0.3 wt% lactic acid and water. The contact angles of alkaline- color-treated weathered hair treated with n-HEA/SPDA and 19-MEA/SPDA condition- ers after one instance of shampooing with a plain shampoo were 76.4° ± 2.5° and 79.6° ± 2.6°, respectively, which were higher than that of alkaline-color-treated weathered hair but lower than that of normal hair. We demonstrated that there were signifi cant differ- ences in the contact angles between normal hair and alkaline-color-treated weathered hair treated with n-HEA/SPDA or 19-MEA/SPDA by conducting analysis of variance (ANOVA). The contact angle of alkaline-color-treated weathered hair treated with 18- MEA/SPDA conditioner after one instance of shampooing with a plain shampoo was 88.0° ± 3.1°. This showed that there was no signifi cant difference in the contact angles between normal hair and alkaline-color-treated weathered hair treated with 18-MEA/ SPDA. In addition, there were signifi cant differences in the contact angles between alka- line-color-treated weathered hair treated with 18-MEA/SPDA and alkaline-color-treated weathered hair treated with n-HEA/SPDA or 19-MEA/SPDA. The fact that the surface of alkaline-color-treated weathered hair treated with the 18-MEA/SPDA complex could maintain its hydrophobicity even after one instance of shampooing with a plain shampoo, while the hair treated with other complexes could not create a hydrophobic surface, indi- cated that the anteiso-branch moiety of 18-MEA was vital for providing sustainable hy- drophobicity to alkaline-color-treated weathered hair. The question remained as to how the anteiso-branch moiety of 18-MEA in the 18-MEA/SPDA complex provided the per- sistent hydrophobicity to the alkaline-color-treated weathered hair surface compared to the straight-chain moiety of n-HEA in n-HEA/SPDA or the iso-branch moiety of 19- MEA in 19-MEA/SPDA. Figure 2. Contact angle of hair after shampooing. The bars represent means for n = 10 the whiskers repre- sent the standard deviations. The asterisks indicate p-values obtained from ANOVA analysis. (a) Normal hair. (b) Alkaline-color-treated weathered hair. (c) Alkaline-color-treated weathered hair treated with n-HEA/ SPDA. (d) Alkaline-color-treated weathered hair treated with 19-MEA/SPDA. (e) Alkaline-color-treated weathered hair treated with 18-MEA/SPDA.

JOURNAL OF COSMETIC SCIENCE 514 DEPOSITION OF FATTY ACID The amount of fatty acid sorption of alkaline-color-treated weathered hair treated with n-HEA/SPDA, 19-MEA/SPDA, and 18-MEA/SPDA conditioners and after one instance of shampooing measured by LC-MS were 25.4 ± 6.4 μg/g-hair, 24.2 ± 3.8 μg/g-hair, and 18.7 ± 6.0 μg/g-hair (for n = 3), respectively. There were no signifi cant differences be- tween these three kinds of fatty acid in the amount of fatty acid sorption by ANOVA. The results indicated that the amount of fatty acid sorption on alkaline-color-treated weath- ered hair was not just directly related to the branch structure of fatty acid. In our previous paper a surface model of hair treated with 18-MEA/SPDA was proposed, in which 18- MEA/SPDA formed a layer 1 nm in thickness, having a hydrophilic area of molecules binding tightly to the surface and orienting the hydrophobic part to the air interface at an angle of approximately 25° (14). In this model the anteiso-branch moiety of 18-MEA does not interact with the surface directly, and therefore it seems reasonable that there were no signifi cant differences in the deposition of fatty acid among the alkaline-color- treated weathered hair samples treated with n-HEA/SPDA, 19-MEA/SPDA, and 18- MEA/SPDA conditioners. AFM INVESTIGATION USING MICA SURFACE It is very diffi cult to examine the exact situation of an 18-MEA/SPDA layer adsorbed onto an alkaline-color-treated weathered surface, since the surface of hair is too rough for AFM investigation. In order to investigate the thickness and physical proper- ties of the layer formed by n-HEA/SPDA, 19-MEA/SPDA, or 18-MEA/SPDA, an atom- ically fl at surface is needed for the AFM observation. In this study, mica was also used for AFM investigation as a hydrophilic model surface instead of hair, as in our previous study (14), although it might be open to question whether these surfaces would behave differently due to the different compositions of the surfaces. We believe, however, that the attachment and orientation of these complexes could be similar in human hair. The AFM height images of the absorbed layers on mica surfaces treated with n-HEA/ SPDA (a), 19-MEA/DAPS (b), and 18-MEA/SPDA (c) conditioner solutions (Figure 3) showed that the all conditioner formulations were homogeneously adsorbed on the mica surfaces. The mechanical properties of the adsorbed membranes were analyzed using the AFM scratching method, as shown in Figure 3. A layer that is diffi cult to remove indicates that the adsorbed layer is strongly bound to the surface. The images were corrected after 1-μm × 1-μm scratching tests by rastering a tip with constant force. The images of the absorbed fi lms treated with n-HEA/SPDA (a), 19-MEA/SPDA (b), and 18-MEA/SPDA (c) showed small grooves. The results indicated that the n-HEA/ SPDA, 19-MEA/SPDA, and 18-MEA/SPDA conditioner solutions adsorbed homoge- neously on the mica surfaces and had a high wear resistance. The observation that the adsorbed layer on the mica surfaces treated with the n-HEA/SPDA, 19-MEA/SPDA or 18-MEA/SPDA conditioners had a high wear resistance corresponded to the observation that there were no differences in the amount of fatty acid adsorbed on alkaline-color- treated weathered hair. The fact that the adsorbed layers on the mica surfaces treated with the n-HEA/SPDA, 19-MEA/SPDA, or 18-MEA/SPDA conditioners had a high wear resistance, however, did not correspond with the observation that the anteiso-branch