Recently, we have reported that keratin film consisting of human hair proteins is a useful substitute for hair samples to evaluate the friction and adsorption by processing commercial shampoo and conditioner products. The frictional coefficient of the keratin film whose MIU value was 7–8 fold more than that of a hair strand, was decreased after undergoing shampoo-conditioner treatment. Since the commercial products contained a number of ingredients more than thirty, the compound to affect the friction remained unclear. Thus, we designed and prepared the model shampoo (MS) and conditioner (MC), and examined their effects on the friction of the keratin by a KES system. Like commercial products, the MIU value was significantly decreased when the keratin film was treated with MC and MS+MC. Among the candidate substances, stearyltrimethylammonium chloride (STAC) and stearylalcohol were efficient to decrease the MIU value of the keratin film. The degree of the MIU decrease was dependent on the concentration of STAC. The adsorption of STAC to the keratin film was detected using a fourier-transform infrared spectroscopy (FT-IR). The peak-heights at 2855 and 2930 cm-1 were proportional to the amount of STAC added. These results suggest that the binding of STAC will result in some changes to the film surface and reduce the MIU values in a dose-response. The treatments of the dimethyl silicone and aminopropyl dimethicone also caused the decrease of the MIU values and their adsorption was detected using an energy dispersive X-ray spectrometry (EDS). Taken together, this combination will be an effective procedure to screen the material that affects tactile sensation of hair.
