LIGHT SCATTERING IN HAIR CUTICLES 355 INSTRUMENTATION Scanning electron microscope (SEM) observations were performed on the hair surface and sections. SEM observations were carried out using a Hitachi S-4000 scanning electron microscope. For the observations of transverse and longitudinal sections, the hair fibers were embedded in an epoxy resin (Epon802) and cut using an ultramicrotome (Nova Ultratome) equipped with a glass knife. All samples were coated with a layer of Pd/Pt in a sputter-coating unit (Jeol JFC-1100). Transmission electron microscope (TEM) observations were performed in order to ob- serve the fine structure of the cuticle cells. The hair samples were embedded in an Epon802 resin after blow-drying in a combing process. Ultrathin sections (100 nm) were prepared using the ultramicrotome for longitudinal sections of the hair fiber. TEM observations were conducted using a Jeol JEM-2000FX transmission electron micro- scope. The secondary structure of the cuticle keratin was examined by Fourier transform infrared attenuated total reflectance (FT-IR/ATR) spectroscopy. The spectra were col- lected on a Bio-Rad FTS-60A spectrometer with the use of a zinc selenide crystal designed at a 45-degree angle of incidence. The fibers were immersed in de-ionized water followed by 30 seconds of blow-drying at 70øC, and the number of applied cycles was 5 or 30 times each. Measurements of the moisture content at the fiber surface were performed using near- infrared photoacoustic spectroscopy (NIR-PAS). The NIR-PAS instrument is an origi- nally constructed in vivo NIR-PAS spectrometer equipped with a hand-made measure- ment cell and a laser diode as a thermal source. A total of 30 fibers per sample were used for PAS analysis, and the variation in moisture in the cuticle cell was examined after blow-drying. In order to maintain uniformity in the humidifying conditions, all the PAS measurements were performed in an environmental control room (23øC/75% RH). RESULTS AND DISCUSSION STRUCTURAL CHANGES IN THE HAIR CUTICLE Many consumers perceive some changes in their hair such as disentangling, feel, bounce, shine, etc., after using a hair dryer. The half-head test was carried out in order to elucidate the effect of blow-drying applied to hair in a wet condition (Figure 1). The left half-head was dried by applied hot air drying, and the right half-head was air-dried. It was confirmed that the left half-head showed a whitish and powdery appearance, and consequently hair gloss was suppressed. Optical microscope observations of the hair fiber revealed that several glittering speckles appeared after heat drying (Figure 2). Several colored glittering speckles, sometimes red, blue, green, etc., were shown in the high- magnification optical microscopic image (Figure 3), suggesting light reflection due to interference of light at the cuticle layer. SEM analysis results of fiber surfaces before and after blow-drying are shown in Figure 4. The existence of concave-shaped scale edges owing to cuticle layer splitting are shown (circled in Figure 4) in blow-dried fibers. Through SEM observations of transverse and longitudinal sections, it was confirmed that structural changes caused by blow-drying also occurred between inner cuticle layers (Figure 5).

356 JOURNAL OF COSMETIC SCIENCE Hot dry Ardry R. Figure 1. Half-head trial. Left half-head after applied hot-air drying (70øC/30 sec). The other half was air-dried with a whitish appearance. a) b) , O0 rn Figure 2. Optical microscope observations of hair tresses (a) before and (b) after hot-air blow-drying at 70øC for 30 sec. The hair damage caused by blow-drying has been reported in the literature (5-8). Thermal treatment of hair operating in the temperature range above 100øC caused irreversible structural changes of hair fiber due to the transformation of the keratin secondary structure (5-7). Additionally, it was reported that blow-drying cycles at 75øC caused crack formation at the edges of the cuticle cell as a result of swelling and deswelling of the hair fiber (8). Compared to these phenomena, however, the generation