46 JOURNAL OF COSMETIC SCIENCE SOAK TESTS Soak tests were performed on damaged hair, with and without commercial conditioner application. A dry hair fiber was taken from a switch, and a sample was cut from the fiber (approximately 7-mm long) for coefficient of friction measurements. An adjacent sample was also taken from the fiber and placed in a small beaker filled with de-ionized water. The sample was subjected to the aqueous environment for five minutes, which is representative of a typical exposure time when showering/bathing, then immediately analyzed with AFM. It should be noted that hair becomes saturated when wet in about one minute and remains saturated if kept in a humid environment. It was determined from unpublished results that if the wet hair was exposed to the ambient environment for more than 20 minutes while in the AFM, the hair became dry and the coefficient of friction became similar to that of dry hair. Thus, coefficient of friction measurements were made within a 20-minute time frame for each sample. RESULTS AND DISCUSSION SURFACE ROUGHNESS AND FRICTION FORCE MAPS OF VARIOUS HAIR SAMPLES Figure 4 displays the representative surface roughness and friction force maps for dam- aged hair and the seven different treatments. When conditioner is applied to the surface, a pattern of high friction is shown in the area surrounding the bottom edge of the cuticle. Likewise, the application of a BTMAC surfactant (with no silicone deposition) or a BAPDMA surfactant (no silicone deposition) results in similar friction features. This is believed to be an area of conditioner accumulation that causes increased friction due to meniscus effects. Friction maps for the PDMS blend of silicone (at both low and high deposition levels) added to the BTMAC surfactant do not show this increase as readily, suggesting that this type of silicone is not a contributor of high friction force on the nanoscale. This can be due to the fact that a PDMS-type silicone is fairly mobile on the surface and thus does not cause the same meniscus effects as the AFM tip rasters through it. Also, the surface energy of the PDMS silicone is believed to be lower than that of the cationic surfactants. As a result, the meniscus force affecting the friction between the AFM tip and silicones in the conditioner is lower than that of conditioner without silicones. Thus, the overall friction force will be lower. For high deposition levels of amino silicone, however, we see that there is a high variation of friction force and a more distributed layer. The amino group typically is less mobile and harder to move, which accounts for a different slip plane flow than that of PDMS silicone. FORCE VOLUME (ADHESIVE FORCE) MAPS OF VARIO US HAIR SAMPLES Figure 5 displays the adhesive force maps for damaged hair and the seven different treatments. As shown in the legend, a lighter area corresponds to a higher tip pull-off force (adhesive force). We observe that damaged untreated hair has relatively low ad- hesive force, which is more or less consistent over the hair surface. In nearly all cases, addition of a conditioner treatment caused an increase in meniscus forces, which in turn increased the adhesive pull-off force between the AFM tip and the sample. Observing the

NANOTRIBOLOGICAL PROPERTIES OF HAIR 47 Surface roughness Friction force Damaged (untreated) 250-------� (nm) 5 0 5µm Damaged treated (commercial) 5µm 250.------�---� 025--- -- - {nm) (VJ -250L----------' -0,25-- - - - - - 5 5 0 5µm (BTMAC surtactant, no silicone) 0 5µm 250 -- - - - - - O 25 .---------, �� M -250L__________., 5 -0 25 5 5µm 0 5µm (PDMS blend silicone, low deposition) 250--- - - - - o.2s- - -------, (nm) L-- ------ --' (V ) � 5�--------5 5µm 0 (PDMS blend silicone, high deposition) 5µm 250...,..----- - 0.25---------, (nm) L--- -- - - - --' (VJ .l I -250 5 -0.25L--- - - ----' 1µm 0 5µm 0.5V 0 5µm Surface roughness Friction force (Amino silicone, low deposition) 250.----------� (nm) -250---------' 0 5µm 0 5µm (Amino silicone, high deposition) 250---------, 0.25-- - -- - (nm) (VJ -250-- - - - - - -0.25L..__ ________., 5 5 0 5µm (BAPDMA suliactant, no silicone) 0 5µm 250- - - - - - 0.25--��- ---, (nm ) - ------- M � 5 � - -- - - - - 5 1µm 0 5µm 05V 0 5µm Figure 4. Surface roughness and friction force maps of damaged hair with various treatments.