2010 TRI/PRINCETON CONFERENCE 263 The same hair probe setup was also used for a more detailed investigation of the friction properties between single hair fi bers. In this case, we focused on the lateral signal which is detected by the photodiode. The directional friction effect of human hair is well known. As with most animal fi bers, it is less effective to move over the hair in a root to tip direc- tion than in the tip to root direction, because of anisotropic orientation of hair cuticles. A typical friction loop of the approach (upper curve part) and the retraction (lower curve part) is observed (Figure 6). The distance is 1 μm. On average, the spacing between hair cuticle edges is around 5 μm. Consequently, this measurement is done on the cuticle surface between the edges. Increasing the lateral range of measurement from 5 μm to 25 μm, the cuticle edges be- come apparent in the friction loops. This ratchet mechanism at the cuticle edges is also shown by LaTorre and Bhushan (5) during friction loops between a cantilever and a hair surface. A complete in-situ experiment is shown in Figure 7: The black line shows a fric- tion loop after the system was rinsed with 40 ml water with a velocity of 0.20 ml/s. Comparable to the latter friction loop, the cuticle edges cause a higher signal. The appli- cation of 40 ml Polyquaternium-87, a new conditioning polymer for hair care (1), took also 200 s and confi rms the assumption that the cationic polymer smoothes the cuticle edges. After rinse-off with water, the signal of the cuticles appears smoother compared to the untreated hair without PQ-87 treatment. The peaks in the curves are the cuticle edges, in the opposite direction this signifi cant feature is less pronounced. SUMMARY In this work, the effects of different conditioning systems applied in shampoos were in- vestigated. We used physical methods like combing and friction measurements, UST, and AFM to observe friction phenomena on different scales directly on hair. This is an approach to complement sensoric evaluations with an objective in-vitro method to screen new chemistries and to do a structure property mapping. Figure 6. Friction loop on one cuticula scale crossed cylinders scan distance 1 μm.
JOURNAL OF COSMETIC SCIENCE 264 REFERENCES (1) Polyquaternium-87 = Luviquat® Sensation, BASF. (2) E. Max, W. Häfner, F. W. Bartels, A. Sugiharto, C. Wood, and A. Fery, A novel AFM based method for force measurements between individual hair strands, Ultramicroscopy, 110, 320–324 (2010). (3) P.A.L.M. Microbeam System, 355 nm UV-light, gas laser, ZEISS, Germany. (4) Atomic Force F&E GmbH, Germany. (5) C. LaTorre and B. Bhushan, Nanotribological characterization of human hair and skin using atomic force microscopy, Ultramicroscopy, 105, 155–175 (2005). Figure 7. Friction loops after subsequent treatments in a fl uid cell: In situ friction loop in water, followed by application of Luviquat® Sensation (INCI PQ-87) at a concentration of 200 ppm, followed by rinse-off with water.
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