The glass transition of human hair and its dependence on water content were determined by means of differential scanning calorimetry (DSC). The relationship between the data is suitably described by the Fox equation, yielding for human hair a glass transition temperature of T(g) = 144 degrees C, which is substantially lower than that for wool (174 degrees C). This effect is attributed to a higher fraction of hydrophobic proteins in the matrix of human hair, which acts as an internal plasticizer. The applicability of the Fox equation for hair as well as for wool implies that water is homogeneously distributed in alpha-keratins, despite their complex morphological, semicrystalline structure. To investigate this aspect, hair was rendered amorphous by thermal denaturation. For the amorphous hair neither the water content nor T(g) were changed compared to the native state. These results provide strong support for the theory of a quasi-homogeneous distribution of water within alpha-keratins.

The time-dependent bending recovery of human hair fibers was investigated for a variety of relative humidities and aging times. The data were analyzed on the basis of a viscoelastic filament/matrix model and the Denby-equation, containing the parameter K as the ratio of the elastic bending rigidities of the matrix and the filaments and the Kohlrausch-Williams-Watts (KWW) function as relaxation function. The first stage of the analysis ascertained that the recovery curves shift with aging time on the time scale with the expected aging rate of l % 1. The second stage showed that the shape factor of the KWW function exhibits a mean value across the aging and humidity range of m ¼ 0.28, which is close to the "universal" value of 1/3. On this basis, it was found that virtually no change occurs for the modulus ratio for low water contents up to about 10%, being constant at K 0 ¼ 6 .1, while linearly decreasing beyond this threshold. The reduced, characteristic relaxation time drops on the log-time scale from logs r (0) ¼ 0.47 for the dry fiber linearly with water content, covering about two thirds of a decade for 0-20% water content. With the pronounced humidity dependence of the parameters, hair shows what is termed hydro-rheologically complex (HRC) in analogy to thermo-rheologically complex behavior. Using the HRC approach, the dynamical mechanical performance of hair (1 Hz) was calculated for a range of water contents and aging times and found to be in good general agreement with experimental data.

by microfluorometric scanning that the negative charges generated in the cuticle surface can be used to bind low-molecularweight quaternary conditioners. This process can be considered as 'relipidation' or 'refatting of the scale faces. We have shown in earlier studies (1) that this entire process of oxidation-induced 'delipidation' and subsequent 'relipidation' of the acidic scale faces with a cationic conditioning molecule can also be reliably quantified by X-ray photoelectron spectroscopy (XPS). Furthermore, single-fiber wettability scanning using the Wilhelmy technique, which is highly sensitive to any changes in surface chemistry, is well-suited to detect and characterize treatmentinduced changes in the chemical nature of the hair surface from hydrophobic to hydrophilic.pp. 13-22 Natural moisturizing factors in the stratum corneum I. Effects of lipid extraction and soaking (M.V., A.L.R) Natural moisturizing factor (NMF) is essential for appropriate stratum corneum hydration, barrier homeostasis, desquamation, and plasticity. It is formed from filaggrin proteolysis to small, hygroscopic molecules including amino acids. We hypothesized that common lipid extraction and soaking in water would alter the level of NMF in the upper stratum corneum (SC) and its biophysical properties. A novel method of measuring and quantifying the amino acid components of NMF is presented. Adhesive tapes were used to collect samples of the SC and were extracted with 6 mM perchloric acid for analysis by reverse-phase highperformance liquid chromatography (HPLC).The HPLC results were standardized to the amount of protein removed by the tapes. An increase in NMF was found with increased SC depth. Also, the combination of extraction and soaking was found to increase NMF loss relative to control or to extraction or soaking alone. Our results indicate that common skin care practices significantly influence the water binding materials in the upper SC. The findings have implications for the evaluation and formulation of skin care products.pp. 23-29 Natural moisturizing factors in the stratum corneum II. Regeneration of NMF over time after soaking (M.V., A.L.R) The detrimental effects of prolonged water exposure on skin are well known. Information on the effects of short-term exposure, e.g. during bathing, showering, and hand washing, on Natural moisturizing factors (NMF) levels is limited. In an attempt to isolate the effects of soaking on the NMF, a time course for skin sample collection was devised in which adhesive tapes were applied 0.5 and 4 h after soaking of the treated arm. Significant decreases in NMF levels, quantified by high-performance liquid chromatography analysis of serial tape strips, were observed 0.5 h after soaking, with a replacement of NMF occurring by the four-hour mark. This replacement corresponds to a parallel rebound in skin pH also observed at these times. Stratum corneum (SC) hydration values, measured instrumentally as the rate of moisture accumulation (MAT), however, were depressed 0.5 h post-soaking and remai...