Friction and Surface Temperature of Wet Hair Containing Water, Oil, or Oil-in-Water Emulsion

Journal of Oleo Science Copyright 2016 by Japan Oil Chemists Society doi : 10.5650/jos.ess15250 Friction and Surface Temperature of Wet Hair Containing Water, Oil, or Oil-in-Water Emulsion Yuuki Aita and Yoshimune Nonomura * Department of Biochemical Engineering, Graduate School of Science and Engineering, Yamagata University (4-3-16 Jonan, Yonezawa 992-8510, JAPAN) Abstract: The surface properties and the tactile texture of human hair are important in designing hair-care products. In this study, we evaluated the temporal changes of friction and temperature during the drying process of wet human hair containing water, silicone oil, or oil-in-water (O/W) emulsion. The wet human hair including water or O/W emulsion have a moist feel, which was caused by the temperature reduction of approximately 3-4. When human hair is treated with silicone oil, more than 60% of the subjects felt their hair to be slippery and smooth like untreated hair. Treating hair with O/W emulsion after drying made the subject perceive a slippery feeling because the surfactant reduced friction on the hair surface. These results indicated that both friction and thermal properties of the hair surface are important to control the tactile texture of the human hair. Key words: human hair, friction, temperature, tactile feel, emulsion 1 INTRODUCTION The tactile texture of the human hair is one of the most important factors in designing shampoos, hair conditioners, and hair styling agents. Human hair with soft and breezy texture is desirable for many customers 1. Therefore, the hair s tactile texture and frictional properties were evaluated after treatment with hair-care products 2, 3. Previous studies have shown that the morphology and mechanical properties of human hair change by contact with water. Bhushan and Speakman et al. indicated that an increase in moisture increases the elasticity and frictional resistance of human hair 3, 4. In addition, Wolfram found a deformation of the cuticle layer on the hair s surface due to swelling 5. Furthermore, the surface properties of human hair are changed by adsorption of oil or surfactant molecules. Adsorption of the silicone oil and anionic surfactant 2, 6 decreased the frictional resistance of human hair whereas that of the cationic surfactant made the hair hydrophilic 7. The forces between the hair fibers in the cationic surfactant solution can be well explained by a Derjagin Landau Verwey Overbeek interaction. On the other hand, the cationic surfactant modifies these interactions in a manner entirely consistent with the adsorption behavior 8. Lee et al. characterized the adsorption and lubricating properties of the polycation PEG graft copolymer poly l-lysine -graft-poly ethylene glycol on human hair sur- faces and found that the adsorbed graft copolymers act as a boundary lubricant 9. Sadaie et al. employed a cantilever modified with a self-assembled monolayer as a hair-model-probe for friction force microscopy to measure the friction between hair fibers and hair-like surfaces. They concluded that the lack of a fat layer is a major cause of strong friction detected at the hair tip and at the striations of the hair root 10. These physical phenomena affect the tactile texture of human hair. For example, silicone oil, which is adsorbed on the hair surface, induced a smooth feeling 11 whereas the frictional resistance increase was caused by bleaching and led to hindrance while combing 2, 12. In addition, the surface condition of human hair was improved by the adsorption of the stearoxypropyldimethylamine and 18-methyleicosanoic acid 13. However, the previous analytical methods, which focused only on the frictional properties of human hair, are not suitable because the tactile texture is governed several factors, including hardness, warmness, friction, and surface shape 14. Therefore, to understand the cognitive mechanism of the tactile texture of human hair, it is necessary to consider multiple physical properties. In this study, we evaluate temporal changes in frictional force during the drying process of wet human hair containing water, silicone oil, or oil-in-water O/W emulsion, by using a friction meter * Correspondence to: Yoshimune Nonomura, Department of Biochemical Engineering, Graduate School of Science and Engineering, Yamagata University, 4-3-16 Jonan, Yonezawa 992-8510, JAPAN E-mail: nonoy@yz.yamagata-u.ac.jp Accepted January 22, 2016 (received for review October 31, 2015) Journal of Oleo Science ISSN 1345-8957 print / ISSN 1347-3352 online http://www.jstage.jst.go.jp/browse/jos/ http://mc.manusriptcentral.com/jjocs 493

Y. Aita and Y. Nonomura with a human finger-like contact probe. In addition, we measure the hair surface temperature through infrared thermography. 2 EXPERIMENTAL PROCEDURES 2.1 Materials Human hair bundles black hair, 30 cm length, 10 g weight were purchased from Beaulax Co., Ltd Saitama, Japan. The water was purified with a Demiace DX-15 Series cartridge-type Deionizer Kurita Water Industries Ltd., Tokyo, Japan. Silicone oil octamethyltrisiloxane, KF- 96L-1cs and silicone surfactant polyethylene glycol methyl ether dimethicone 11 EO, KF-6011 were obtained from Shin-Etsu Chemical Co., Ltd Tokyo, Japan. Nonionic surfactant polyethyleneglycol monolaurate 12 EO, Emanon 1112 and anionic surfactants sodium lauryl sulfate, Emal 10PT, sodium polyoxyethylene lauryl ether sulfate, Emal 270J were provided by Kao Corporation Tokyo, Japan. The composition of the applied O/W emulsion was surfactant:water phase:oil phase 10:45:45 wt:wt:wt. The surfactant was a mixture of polyethyleneglycol methyl ether dimethicone 11 EO, polyethyleneglycol monolaurate 12 EO, and sodium lauryl sulfate 1:1:0.005, wt:wt:wt. First, water 4.5 g and the surfactant 1.0 g were mixed with a vortex mixer Vortex-genie 2, Scientific Industries Co., New York, America for 1 min. Then, the silicone oil 4.5 g was added and stirred for 5 min to prepare O/W emulsion. The obtained mixture was still a fluid when the grain size of the oil droplets reached several tens of μm. The emulsion state was maintained for more than 30 days; however, the separation of a water phase was observed within a day after the preparation. 2.2 Treatment and tactile evaluation of human hair The hair bundles were washed with 5 wt aqueous solution of sodium polyoxyethylene lauryl ether sulfate and were rinsed under running water. The wet hair bundles were compressed between paper towels under 1.2 10 3 Pa for 10 s to remove the excess water. After combing, the bundles were dried with a hair dryer EH790, Panasonic Corporation, Osaka, Japan. The hair bundles were moisturized with water, silicone oil, or the O/W emulsion as follows. The pretreated hair bundles were immersed in 150 ml water, silicone oil, or the O/W emulsion for 20 min. The hair bundles were compressed between paper towels under 1.2 10 3 Pa for 10 s to remove the excess liquids. The tactile evaluations were achieved for the wet hair before and after drying. When six subjects rubbed the hair bundles with their thumb, index finger, and middle finger of their dominant hand, they described the hair texture using from 62 different Japanese words. During the evaluation, the hair bundles were hung on a holder. These descriptions were classified into 10 tactile dimensions including soft, hard, dry, moist, slippery, sticky, smooth, rough, cold, and hot feels 15. Then, the typical dimensions were those selected by more than 60 of the subjects. All evaluations were conducted according to the principles expressed in the Declaration of Helsinki. The responsible party at Yamagata University confirmed that the ethics and safety of the present test were acceptable. 2.3 Physical evaluation We evaluated the temporal change in the amount of water, silicone oil, or O/W emulsion in the hair bundles every 30 min during their drying process. Simultaneously, the temperature of the hair surfaces was monitored using an infrared thermometer FLIR i3 FLIR Systems Japan K.K., Tokyo, Japan. The friction measurements were performed using a Tribo master TL201Ts friction evaluation meter Trinity Lab Inc., Tokyo, Japan as shown in Fig. 1. The specifications of the apparatus were as follows: measurement range 0.098 19.6 N, vertical force 0.098 4.9 N, sliding speed 0.1 100 mm s 1, and sliding distance 1 100 mm; the apparatus possessed an AC servomotor. We evaluated the frictional force when the hair bundles on a pedestal were rubbed with a polyurethane contact probe. The contact probe reflected the geometry and mechanical properties of real human fingers, and the probe surface Fig. 1 Images of a a human finger on human hair, b a finger model and c a friction evaluation system. 494

Friction and surface temperature of wet hair contained 29 grooves depth: 0.15 mm carved at 0.5 mm intervals 16. This geometry is similar to the human epidermal ridges, which have depths and widths of 0.11 0.03 mm and 0.46 0.15 mm, respectively 17. The Young s modulus of the contact probe, which was measured using a ZTA20 N force gauge with an EMX-1000 N test stand Imada, Aichi, Japan, was 0.64 0.02 MPa 18. We tightly fixed the hair bundles on a low-profile X-axis steel stage TSDT-601S Sigmakoki Co., Ltd., Tokyo, Japan. The friction conditions were as follows: sliding width 30 mm, sliding speed 30 mm s 1, vertical force 0.294 N, and sampling speed 3 ms. These physical evaluations were performed under room temperature of 26 1 and relative humidity of 51 5. Table 1 Tactile dimension of tactile feel of human hair. Liquid Condition Tactile dimension Water Wet Moist, Sticky, Slippery Dry Slippery, Dry, Smooth, Soft Silicone Oil Wet Slippery, Dry, Smooth Dry Slippery, Dry, Smooth, Soft O/W emulsion Wet Moist, Slippery Dry Slippery, Moist Dry Slippery, Dry, Smooth 3 RESULTS 3.1 Tactile texture of wet human hair Table 1 shows the tactile characteristics of wet hair. Here, the elapsed time after removal of excess liquids with paper towels is defined as t, and the wet hair condition corresponds to t 0 whereas the dry hair condition means t 300, 120, and 360 min for water, silicone oil and O/W emulsion, respectively. The tactile texture of the wet human hair including water was described as moist, sticky, and slippery ; however, when silicone oil was included, the subjects indicated slippery, dry, and smooth textures. When the O/W emulsion was applied, many subjects selected only moist and slippery and did not choose sticky. After drying, the hair treated with water or silicone oil was described instead as slippery, dry, smooth, and soft ; their texture was similar to that of untreated human hair. However, human hair treated with the O/W emulsion was described as slippery and Fig. 2 Temporal changes in the friction coefficient for dry human hair. moist. These results indicate that the texture of the wet human hair varies with the moisturizing medium. 3.2 Friction and surface temperature of dry human hair Figure 2 shows the profile of the friction coefficient μ of dry human hair. Here, we defined the static friction coefficient as the maximum value just after starting the experiment, and the kinetic friction coefficient as the average value of the friction coefficient in the steady state. The Fig. 3 Thermographic images of human hair treated with liquids: a dry condition b wet hair including water, c silicone oil, and d O/W emulsion. 495

Y. Aita and Y. Nonomura friction coefficient increased to 1.56 after 0.11 s after starting the finger model, and decreased to 0.34 at steady state. Thereafter, the friction coefficient remained constant. A similar friction profile was observed for all friction conditions. Figure 3 a shows the thermographic image of dry human hair. The temperature at the central area of the dry hair bundle was 25, which was almost equal to the room temperature. 3.3 Friction and surface temperature of wet human hair including water Figure 4 a shows the friction coefficient and temperature temporal changes for the hair bundle treated with water. After soaking the hair bundle in water and removing the excess water with paper towels, the weight of water in 1.0 g of hair W W was 0.51 g. Then, the weight W W decreased to 0.01 g after drying for 300 min. Although the water composition decreased, the frictional force on the hair was almost constant; the frictional coefficient was 0.3 at 5 and 300 min after the beginning of the evaluation. Previous studies showed that the friction coefficient of the wet hair is higher than that of dry hair, because the hair surface structure changes by the contact with water 19. However, in the present study, the friction coefficient for the wet hair including water is equivalent to that of the dry hair. We guess that the difference is caused by the friction conditions such as the material of probe, the amount of water on the hair surface, and the swelling condition of the human hair. On the other hand, a significant change was observed in the temperature; it increased from 21.8 to 25.0 during the same interval. In other words, human hair temperature is reduced by the heat of vaporization when human hair contains a large amount of water. 3.4 Friction and surface temperature of wet human hair including silicone oil The frictional and thermal behavior of wet human hair including silicone oil was quite different from that of water Fig. 4 b. After soaking the hair bundle in silicone oil and removing the excess with paper towels, the weight of the silicone oil in the hair Wo was 0.34 g in 1.0 g of hair. Then, the weight decreased during the drying process to 0.01 g, 90 min into the experiment. Wet human hair including silicone oil requires less time to dry than hair with water because the vapor pressure of the silicone oil is less than that of water due to smaller intermolecular interactions 20. Temperature of the human hair was nearly unchanged at 25 during the drying process. On the other hand, the friction coefficient decreases from 0.35 to 0.21 during these 90 min. Just after removal of silicone oil with paper towels, the excess amount of silicone oil exists on the hair surface. The excess silicone oil can increase the friction coefficient and negate the lubricant effect of the silicone oil, because the excess silicone oil binds the hair Fig. 4 Temporal change of the liquid amount in 1.0 g of human hair, kinetic frictional coefficient and temperature : a Wet hair including water, b silicone oil, and c O/W emulsion. fibers with the liquid bridges. 3.5 Friction and surface temperature of wet human hair including O/W emulsion Although the thermal behavior of the wet human hair including O/W emulsion is similar to that including only water, the friction behavior differs from that including 496

Friction and surface temperature of wet hair water or silicone oil Fig. 4 c. After soaking the hair bundle in the O/W emulsion and removing the excess with paper towels, the weight of the O/W emulsion in the hair W O/W was 0.62 g in 1.0 g of hair. Then, the weight decreased to 0.04 g after drying for 360 min. During the drying process, the hair s thermal behavior is similar to that of wet human hair including water; the hair temperature increases from 20.9 to 27.3. In addition, friction changed significantly; the friction coefficient is 0.37 just after the beginning of the experiment, and it is 0.20 at 360 min. These results indicate that the dried emulsion film decreases the friction resistance. 4 DISCUSSION We concluded that the moist feel of wet hair is caused by the reduction of temperature due to water evaporation. In the present study, the moist feel was recognized only for wet human hair including water and the O/W emulsion. In both cases, the reduction in the surface temperature was observed; the temperature decreased approximately 3-4 by using water and the O/W emulsion. On the other hand, the temperature reduction was not observed for wet human hair including silicone oil. The significant temperature decrease of wet human hair including water and the O/W emulsion was caused by the heat produced during water vaporization 44.3 kj/ mol 21, which is 15 times greater than that of silicone oil 22. After drying, the tactile texture of hair, which was treated with water and the silicone oil, was similar with that of the untreated hair. Many subjects cited the words slippery, dry and smooth. On the other hand, the tactile texture of the human hair treated with the O/W emulsion was slippery and moist after drying. This texture was caused by the surfactant layer on the hair surface after drying. The slippery and moist feelings can be induced by the lubricant layer of these surfactant molecules on the hair surfaces 2, 23. 5 CONCLUSION We have developed a tactile evaluation system for human hair to analyze the tactile texture of wet hair including water, silicone oil, or O/W emulsion. The obtained data indicated that the tactile texture depends on the friction and the temperature after drying. The tactile texture is associated with the hair s viscosity affected by the O/W emulsion or the surfactant. These findings are useful for the prescription and design of high-quality hair-care cosmetics. References 1 Nagamachi, M. Kansei engineering as a powerful consumer-oriented technology for product development. Appl. Erg. 33, 289-294 2002. 2 Scott, G. V.; Robbins, C. R. Effects of surfactant solutions on hair fiber friction. J. Soc. Cosmet. Chem. 31, 179-200 1980. 3 Bhushan, B.; Wei, G.; Haddad, P. Friction and wear studies of human hair and skin. Wear 259, 1012-1021 2005. 4 Speakman, J. B. The Plasticity of Wool. Proc. Roy. Soc. B 103, 377-396 1928. 5 Wolfram, L. J. Human hair: A unique physicochemical composite. J. Am. Acad. Dermatol. 48, S106-S114 2003. 6 Yahagi, K. Silicones as conditioning agents in shampoos. J. Soc. Cosmet. Chem. 43, 275-284 1992. 7 Ran, G.; Zhang, Y.; Song, Q.; Wang, Y.; Cao, D. The adsorption behavior of cationic surfactant onto human hair fibers. Colloids Surf. B 68, 106-110 2009. 8 Mizuno, H.; Luengo, G. S.; Rutland, M. W. Interactions between Crossed Hair Fibers at the Nanoscale. Langmuir 26, 18909-18915 2010. 9 Lee, S.; Zürcher, S.; Dorcier, A.; Luengo, G. S.; Spencer, N. D. Adsorption and Lubricating Properties of Poly l-lysine -graft-poly ethylene glycol on Human- Hair Surfaces. ACS Appl. Mater. Interfaces 1, 1938-1945 2009. 10 Sadaie, M.; Nishikawa, N.; Ohnishi, S.; Tamada, K.; Yase, K.; Hara, M. Studies of human hair by friction force microscopy with the hair-model-probe. Colloids Surf. B 51, 120-129 2006. 11 Lim, J. M.; Chang, M. Y.; Park, M. E.; Kwak, T. J.; Kim, J. J.; Lee, C. K. A study correlating between instrumental and consumers subjective luster values in oriental hair tresses. J. Cosmet. Sci. 57, 475-485 2006. 12 Robbins, C. R.; Reich, C. Prediction of hair assembly characteristics from single-fiber properties. Part II. The relationship of fiber curvature, friction, stiffness, and diameter to combing behavior. J. Soc. Cosmet. Chem. 37, 141-158 1986. 13 Tanamachi, H.; Inoue, S.; Tanji, N.; Tsujimura, H.; Oguri, M.; Ishita, M.; Tokunaga, S.; Sazanami, F. Deposition of 18-MEA onto alkaline-color-treated weathered hair to form a persistent hydrophobicity. J. Cosmet. Sci. 32, 31-44 2009. 14 Okamoto, S.; Nagano, H.; Yamada, Y. Psychophysical dimensions of tactile perception of textures. IEEE Trans. Haptics 6, 81-93 2013. 15 Kuramitsu, K.; Aita, Y.; Nonomura, Y. Categorization of sensory words based on tactile dimensions. J. Soc. Cosmet. Chem. 49, 319-327 2015. 16 Kuramitsu, K.; Nomura, T.; Nomura, S.; Maeno, T.; Nonomura, Y. Friction evaluation system with a human 497

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