2010 TRI/PRINCETON CONFERENCE 117 Figure 11. Micrograph of a hair fi ber (φ ~ 64 μm) showing image of surface obtained with no shift in plane of focus (11a). Later the plane of focus (p.o.f.) was shifted in 27 and 32 μm, respectively the white spots in the image are voids with sizes ranging between 3 and 10 μm. The hair fi ber was subjected to fi ve hot-iron treatments at a temperature of 210°C and with a hot-iron speed of 0.2 in/s. form of heat damage. It certainly, involves a process of protein denaturation, melting, aggregation, and shrinkage similar to the one taking place when other types of proteins are exposed to high temperatures during cooking (15). It is interesting to note also that SEM analysis of the broken fragments showed that large air bubbles and micro-pores always coexist together (see Figures 13a and 13b). Figure 12. Micrograph of a hair fi ber (φ ~ 78 μm) before (12a) after (12b) shifting the plane of focus. Figure 12b shows the formation of small voids and air bubbles inside the hair after bring subjected to one hot iron- ing treatment at 220°C with a hot-iron speed of 0.2 in/s. The air bubbles appear as luminous translucent regions by optical microscopy. In Figures 12c and 12d are shown different views of the same fi ber when seen by scanning electron microscopy.

JOURNAL OF COSMETIC SCIENCE 118 EFFECTS OF SOME POLYMERS AND OILS ON THE HAIR SURFACE It should be mentioned here that the application of polymers and oils on the hair surface prior to hot iron application had a signifi cant impact on the heat damage of both cuticle sheath and cortex. For instance, the experiments showed that for temperatures 180°C and normal hot iron speeds, the presence of thick polymer layers on the hair surface led to the formation of pores that were mostly confi ned at the cuticle sheath surface, while the num- ber of pores inside the cortex decreased substantially. This effect can be seen in Figure 14 where it is shown that when a thin polymer layer (~0.5 μm thick) of N-vinylpyrrolidone methacrylamide and N-vinyl imidazole (16) is on the hair surface the number of pores formed inside the cortex is lesser than when the polymer is absent. Also, it was observed that this polymer suppressed the formation of the type of large voids occurring at 210°C Figure 13. Scanning electron micrograph of a hair fi ber (φ~ 68 μm) after being subjected to four hot-iron treatments at 220°C using a low hot-iron speed of ~ 0.2 in/s. Figure 14. Averages of total pore count from areas ~ 0.06 mm2 for two sets of ten hair fi bers (φ~ 72 μm). The bars represent average counts obtained with untreated fi bers (control) and fi bers treated with a leave-on formulation containing 0.1% aqueous solution of N-vinylpyrrolidone methacrylamide and N-vinyl imida- zole (13) after application the excess solution was squeezed with the fi ngers. All hair fi bers were subjected to fi ve hot-iron treatments.