2010 TRI/PRINCETON CONFERENCE 113 obtain a distribution profi le of their size by area (see Figure 6). By using this counting technique in combination with the ability to shift the plane of focus it was soon found that micropore formation occurs mainly at the cortex periphery (see Figure 7). Further analysis based on this counting technique led to three groups of observations related to the mechanism of pore formation. The fi rst group of observations is related to the presence of moisture in the hair fi ber and to changes in its dimensions. These observations revealed that a critical factor in the for- mation of pores is the combination of moisture and fi ber changes in dimensions if the fi ber is not elongated or contracted pore formation is practically non-existent. For in- stance, in Figure 8 it can be seen that the number of pores as a function of hot-iron treat- ments, at normal speeds, is very low when the fi bers are dried, either, with or without elongation. However, in the same fi gure it can be seen that when the fi bers contain mois- ture the overall number of pores increases very rapidly although, the increments are substantially higher when the fi bers are wet and elongated. The term “elongation” refers here to fi ber extension created by fi ber dragging due to hot-iron friction. Pores were also Figure 5. Micrograph of a hair fi ber (φ ~ 76 μm) subjected to fi ve treatments of hot ironing showing the presence of pores at a depth of 10 μm inside the cortex (5a). The image in Figure 5a was then thresholded to create a binary image by using image analysis software in order to separated the pores from a black back- ground (Figure 5b). Figure 6. Micropore count and profi le distribution by pore size obtained in a fi ber area of 0.06 mm2 by im- age analysis.

JOURNAL OF COSMETIC SCIENCE 114 formed when fi bers containing moisture underwent longitudinal free contraction upon contact with a hot plate at temperatures ranging between 180 and 200°C. The second group of observations is related to the effect of temperature as shown in Fig- ure 9 where it can be seen that signifi cant levels of pore formation start to occur around 150°C, after which the number of pores increase monotonically with temperature for a fi xed number of hot-iron cycles. Finally, the third group of observations relates to the occurrence of fi ber super-contraction. Namely, it was observed that hair fi bers which were hot ironed, elongated, and with pores in their cortex underwent later super-contraction after they were wet and/or re-heated again. Also, hair fi bers that were immersed in water/ ethanol solutions showed high levels of pore formation after contacting hot surfaces (180–200°C). Table I lists the degree of super-contraction associated to the various levels of elongation during hot ironing. Super-contraction and denaturation are common phe- nomena in keratin fi bers and have been associated to the melting and disarray of ordered protein structures. These phenomena have been reported to occur as a consequence of Figure 7. Pore count in an area of 0.06 mm2 as a function of distance toward the center of the cortex for a set of four fi bers of φ ~ 72 μm subjected to ten hot-iron treatments at 180°C using a hot-iron speed of 1 in/s. Figure 8. Graph showing total number of pores in an area of 0.06 mm2 as a function of hot-iron treatments (T ~ 180°C and hot-iron speed ~ 1 in/s) with moisture and elongation as parameters. The content of moisture in the hair fi ber for the wet and dry conditions corresponded to equilibration at 82% and 10% RH, respec- tively. The fi ber elongation produced after hot ironing was ~4%.