PENETRATION OF OILS INTO HAIR FIBERS 291 extent, increased diffuse reflectance may be explained by mineral oil residues, especially around the scale edges. Thus, using a goniophotometer as an optical tool to study the surface condition of the hair fiber, we conclude that mineral oil forms a smooth and stable film on the top of the cuticular sheath. Mineral oil does not penetrate extensively into the hair fiber in a 24-hour period, not even at elevated temperatures. Reduction in peak intensity after heat treatment is likely to be due to the penetration of a small amount of oil into the cuticular sheath, leaving most of it on the surface. In Figure 7 A the GP intensity scans are shown for untreated Indian hair fiber recorded in the R-T and T-R positions. Figure 7 also displays the reflectance curves when the same fiber was treated with coconut oil. As described above, a scale angle of 3.6 ° is found from the displacement of specular peaks from the angle of incidence. Coconut oil treatment covers the scale structure and results in sharp specular reflectance with in­ creased peak intensities. After 24 hours the reflection intensity has decreased by a factor of 1.9 (see Figure 7B). However, peaks are still positioned around the angle of incidence. Application of heat treatment for only a few minutes induces a tremendous change in the GP curves, with partial separation, as seen in Figure 7C. Intensity scans from the T-R and R-T positions show a reduction in total intensity and separation. Although multiple reflections are observed, indicating the change in the surface distribution of oil residues, the fiber scale structure is likely to be exposed. Thus, the major amount of deposited oil film on the surface has indeed penetrated into the hair fiber. Dipping the fiber into acetone removes the remaining oil and results in scans matching those of the untreated fiber, as shown in Figure 7D. The scale angle is again 3.5 ° . Results from coconut oil treatment differ from those from mineral oil treatment in several ways. Although measured intensity does not allow exact quantification, the changes in relative intensities can be used as estimates as long as measurements are performed on the same fiber under identical conditions. Hence, the reduction in inten­ sity after 24 hours could indicate the decrease in coconut oil film thickness covering the hair fiber. For mineral oil, the reflected light intensity remained constant. Therefore, we can suggest that coconut oil may have at least partially penetrated the hair fiber within 24 hours. After 24 hours the remaining smooth coconut oil film must be very thin, considering the effect of short-time blow-drying. Several studies conducted at TRI have demonstrated the loosening of scale edges and the formation of half-domes upon heat treatment of hair fibers. Under such conditions, oil can wick into the cuticular structure. If so, then both mineral and coconut oil should penetrate into the hair because their surface tensions are similar. Although oils can wick by capillarity between separated cuticle cells at the surface where the cells may be separated, their penetration into the entire cuticle sheath and the cortex does not occur by capillarity. The fact that coconut oil was found to penetrate and mineral oil does not supports this hypothesis. Because of the much smaller volume, the cuticle can accommodate only a small amount of oil. Therefore, these GP observations show that oils penetrate into the bulk of hair and skin by molecular diffusion. EFFECT OF OTHER OILS ON GP MEASUREMENTS We also conducted measurements with various other plant-derived oils. For hair treated with mustard oil, the scale structure remained covered after 24 hours, even after addi-
292 0.12 0.10 0.08 rn 0.06 · 0.04 0.02 0.00 0 0.07 0.06 0.05 ::::, rn 0.04 · C: 0.03 Q) c 0.02 0.01 0.00 0 JOURNAL OF COSMETIC SCIENCE A coconut oil 2 min. '' T-R ,, ,, II I I 1,1 coconut oil 2 min. 'I \ R-T I, ,t, I 1/ I I untreated R-T/\ 1/ :\ untreated T-R __J1 I I ,, I / 1,1\ 20 40 60 Scattering angle (degrees) B coconut oil 24 hrs. T-R coconut oil 24 hrs. r R-T ( 80 \ ,, I untreated T-R untreated R-r, I ,. I I I r' I \ I' \ I I I I \ I \ I I \ -�--��-....... 20 40 60 80 Scattering angle (degrees) Figure 7. Goniophotometric intensity scans: (A) Individual untreated Indian hair fiber and immediately after coconut oil application. (B) 24 hours after coconut oil application compared to untreated fiber. (C) 24 hours after coconut oil application with short-term heat treatment. (D) After removal of oil film with acetone. tional heat treatment. Also, for hair treated with sesame, ricebran, and olive oils, the scale structure was not apparent from the GP curves even after 24 hours, suggesting no penetration. For olive oil, however, partial separation of reflectance patterns from the
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