J. Cosmet. Sci., 62, 259–264 (March/April 2011) 259 From conditioning shampoo to nanomechanics and haptics of human hair CLAUDIA WOOD, ALBERT BUDIMAN SUGIHARTO, EVA MAX, and ANDREAS FERY, BASF SE (C.W., A.B.S.), and University of Bayreuth, Physical Chemistry II (E.M., A.F.), Germany. Synopsis Shampoo treatment and hair conditioning have a direct impact on our wellbeing via properties like combabil- ity and haptic perception of hair. Therefore, systematic investigations leading to quality improvement of hair care products are of major interest. The aim of our work is a better understanding of complex testing and the correlation with quantitative parameters. The motivation for the development of physical testing methods for hair feel relates to the fact that an ingredient supplier like BASF can only fi nd new, so far not yet toxico- logically approved chemistries for hair cosmetics, if an in-vitro method exists. In this work, the effects of different shampoo treatments with conditioning polymers are investigated. The employed physical test method, dry friction measurements and AFM observe friction phenomena on a mac- roscopic as well as on a nanoscale directly on hair. They are an approach to complement sensoric evaluation with an objective in-vitro method. INTRODUCTION Haptics refer to the tactile sense: External objects or forces are noticed at contact with the body, esp. with hands and fi ngertips. In the skin, there are cutaneous sensual organs with tactile receptors. Their density is highest at the tip of the tounge and of the fi n- gers, which enables to differentiate fi ne structures. The skin on the back has the lowest density of tactile receptors. Tactile quality is noticed and evaluated in sensory assess- ments, where it can be distinguished with expressions like “luxury of touching soft, fl owing hair”. Many hair cosmetic products such as shampoos, conditioning rinses and even hair sprays claim haptic attributes on their packaging like the suppleness of silk, cashmere, and vel- vet or claim attributes like smooth, sleek, silky, and soft. METHODS AND RESULTS In BASF’s application lab, the sensoric or subjective evaluation of hair after various treat- ments is according to a ranking system: “hand mark” of 1=very good to 3=weak, bad. Different attributes of wet and dry hair are ranked as follows:
JOURNAL OF COSMETIC SCIENCE 260 detangling after shampoo application (complemented by physical test method), • combability (complemented by physical test method), • feel of wet and dry hair • positive: well conditioned, silky, soft, smooth ... negative: coated (build-up), oily / greasy, rough / damaged, frizzy ... Additionally, internal und external panel testing as well as external salon testing are ac- cessable for sensoric evaluation. The motivation to develop physical test methods for hair feel is for a raw material sup- plier like BASF to fi nd new, toxicologically not yet approved chemistries for hair cos- metics without touching, so an in-vitro method is mandatory. The physics behind hair feel are an interplay of different forces: Mechanical forces of friction and lubrication during the movement along the hair • surface with a fi nger or a comb, which refl ects smoothness (Figure 1) Mechanical forces during hair bending which refl ects softness and suppleness • Capillary forces only for wet hair, esp. at combing • Mechanical forces of friction and lubrication can be addressed with the Universal Surface Tester (UST), the atomic force microscope (AFM), and dry friction measurements, and they correlate with surface morphology on a certain scale. This paper’s focus is on these phenomena. The phenomena, which lead to quality differences of hair cosmetic treatments, become visible to the observer on different scales: Macroscopically, hair feel and combability can be distinguished on hair bundles, whereas these properties on a micro- or even nanoscale are based on interactions between single fi bers or hair–fi nger or hair–comb. Important for friction is the hair surface morphology, e.g. roughness on a certain scale, as it is known from microscopic images of the cuticula: Virgin hair has fl at cuticula scales, whereas damaged hair shows lifted scales and broken scale edges. Conditioning polymers (Figure 2) have different options to infl uence the hair surface and also haptics of hair. Surface friction coeffi cients of hair with various cosmetic treatments were investigated with a Universal Surface Tester (UST, innowep). The system can be used for wet and dry hair. Caucasian, bleached hair was treated with concept shampoos based on SLES / CAPB, which contained different conditioning systems that are well known on the market: Figure 1. Friction and lubrication during the movement along the hair surface with a fi nger or a comb, which refl ects smoothness.
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