JOURNAL OF COSMETIC SCIENCE 398 more effi cient radiators. For example, if you place a planar thermocouple on the surface of a sweltering asphalt tarmac (ε = 0.93) in mid-summer and then compare the reading to the radiative energy emitted across all emitted wavelengths, Q would virtually correlate with the fourth power of the measured absolute surface temperature of the solid. The hu- man body is nearly a black body radiator, wherein the ε of water is 0.96–0.98, and the ε for human hair is 0.91 (31,32). EFFECT OF FLAT-IRONING ON THE RADIATIVE PROPERTIES OF HUMAN HAIR To gauge the impact of thermal insult on the radiative decay properties of human hair, a virgin hair tress, and an excessively fl at-ironed hair tress (175°C, 0.6 in/min root-to-tip sweeps for 5 min) were simultaneously evaluated after exposure to a convective heat source. After a full day of equilibration at ambient conditions (32–35% RH 20–22°C), to facilitate proper equilibration with ambient water vapor, the extended tresses were exposed to a portable space heater (75°C) that was positioned behind the tresses and pow- ered on high for 5 min. The heater was then rapidly removed and an IR camera was used to immediately monitor the radiative emission of heat from the tresses as they cooled Figure 15. Series of thermal images indicating the kinetics of radiative heat dissipation. The tresses were equilibrated at 32–35 %RH for 24 hours prior to exposing to a 75°C convective heat source. Each image shows the states of the virgin (left) and hot fl at-ironed virgin (right) European dark brown tresses. Images were logged every 10 s, starting at the 5 s mark, and clearly displays the decay of the virgin tress is slower than that of the thermally styled tress.

HAIR SHAPE AND DAMAGE FROM RE-SHAPING HAIR 399 from approximately 70°C to ambient. Figure 15 captures the thermal decay as a series of sequential thermograms and clearly suggests that the virgin tress (left tress) cools to room temperature more slowly than the previously fl at-ironed tress (right tress). Chemical changes that may be tied to the radiative differences are the formation of diisopeptide (amide) or lanthionine cross-links, where diisopeptide cross-linking has been reported to occur at approximately 165°C in keratin (33). Extensive amide cross-linking, via reac- tions between lysine and glutamic/aspartic acid (or their amides) may lead to a reduction in swell volume, thereby limiting the maximum water regain of thermally damaged fi - bers (29). Hence, one possible explanation for differences in the radiative decay rates for virgin and thermally damaged hair is that excessive thermal treatments rework the core fi ber structure and, subsequently, the kinetics of the essential water-binding, hydrogen bonding, and thermal capacity systems of the hair. DYNAMIC SCANNING CALORIMETRY TO MONITOR PROTEIN CHANGES IN THE AMORPHOUS AND CRYSTALLINE REGIONS OF HAIR DSC facilitates an understanding of the physicochemical states of the crystalline interme- diate fi laments (IFs) and the amorphous matrix, or IF-associated proteins (IFAPs). In a DSC experiment, the infl uence of thermal energy on phase transitions, such as melting (Tm) or glass transition (Tg) events, is recorded as a function of applied temperature. Heating or cooling characteristic materials facilitates measurable variations in heat capac- ity (Cp), where ΔCp may be monitored by recording excess, or differential, heat fl ow as a sample undergoes a phase, physical, or chemical transition. Depending on the thermal event, excess heat fl ows to the sample (endothermic), or from the sample (exothermic), relative to the empty sample pan. For example, glass transition (Tg) and melting (Tm) events are endothermic, whereas crystallization processes are exothermic. EFFECT OF THERMAL STYLING ON THE DENATURATION TEMPERATURE OF THE IFS Conveying excessive styling heat to a hair fi ber aggravates the natural organizational structure of the cortex as thermally induced alterations in IFs-IFAPs covalent bonding and/or IFAPs cross-link density decrease the degree of alpha keratin crystallinity (34,35). The denaturation temperature (TD) describes the thermal stability, and the position of TD on the temperature scale is kinetically controlled by the cystine-based cross-link density and viscosity of the non-helical amorphous matrix (36). Further, the thermal energy, or enthalpy (ΔHD), needed to unfold or denature the helix correlates with the structural ri- gidity of the alpha helices bound within the IFs (37). Physically speaking, DSC thermo- grams describe the denaturation of the secondary alpha-helical structure to random coils and beta domains via trends in the magnitudes of the endothermic denaturation tem- perature and enthalpy transitions. HIGH-PRESSURE DSC ANALYSIS OF HAIR In dry DSC methodology, hair is carefully cut into 1–2 mm pieces and then charged into “pinholed” aluminum DSC pans. During the experiment, water is evolved from the pan