2008 TRI/PRINCETON CONFERENCE 139 during the deformation process. This factor would be important in the cases of curly hair. In this work, however, since we are working with essentially straight hair, the parameter is omitted for simplicity. Equation 2 describes the work of pulling in the stationary mode. The resistance to defor- mation in rotational mode is expected to be present in the stationary test as well. Thus, the work measured in the stationary experiment is the sum of the work of pulling in ro- tational mode and the work of friction of the hair tress on immobilized pins. Equation 3 describes the calculated work of friction on pins and defi nes this parameter as apparent hair lubricity. Wrotational = Wfi ber−fi ber friction + Wfi ber stiffness ≡ Apparent stiffness (1) Wstationary = Wrotational + Wfriction on pins (2) Wfriction on pins = Wstationary − Wrotational ≡ Apparent lubricity (3) Finally, in the light of proportionality between forces in stationary and rotational modes we defi ne an apparent friction coeffi cient as the ratio of apparent lubricity or friction on the pins to apparent stiffness as shown in equation 4. Effective friction coefficient Apparent lubricity Apparent stiffness ≡ W W W stationary rotational rotational = − (4) VALIDATION We offer a brief validation to the relevance of the measured parameters next. Table I shows the apparent stiffness, lubricity and the apparent friction coeffi cient of virgin and bleached Caucasian hair tresses. Bleached hair produces substantially less lubricity (i.e. larger work of friction on the pins), 2200 vs. 870 g-force mm than its virgin counterpart. The larger friction of bleached hair is an expected outcome attributed to the damage re- sulting from the bleaching process. Bleached hair also produces higher apparent stiffness, 1340 vs. 1050 g-force mm than virgin. Since the apparent stiffness includes a contribu- tion from hair-hair friction it can not be conclusively stated if the difference is due to the changes in fl exural stiffness or to the friction. Future communication will address the deconvolution between these two parameters. The confl uence of these parameters, how- ever, does not detract from the relevance of the apparent stiffness, as hair-to-hair friction is undoubtedly an important part to the perception of stiffness. Table I also shows signifi cantly different apparent friction coeffi cients. The coeffi cient is predictably lower on virgin hair then on bleached. To ascertain if the apparent friction Table I Comparison between Bleached and Virgin Hair Tress Attributes Stiffness (g-force mm) Friction on pins (g-force mm) Friction coeffi cient Virgin 1050 ± 60 870 ± 70 0.8 ± 0.1 Bleached 1340 ± 100 2230 ± 200 1.7 ± 0.2 2 Bleached combined 3540 ± 270 5390 ± 380 1.5 ± 0.2 Bleached, thinned 1090 ± 40 1650 ± 80 1.5 ± 0.1

JOURNAL OF COSMETIC SCIENCE 140 coeffi cient calculated by equation 4 is an intrinsic hair surface property devoid of particu- lar hair confi guration or mass we carried out the following two experiments. In the fi rst experiment two hair tresses were combined and properties measured. In the second, a bleached hair tress was thinned by about ~15% of its original mass and tested. Table I shows that the described manipulations have not altered the value of the apparent friction coeffi cient. The latter observation has an important implication—the apparent friction coeffi cient is an intrinsic hair surface property that can serve as a basis for comparison of dissimilar hair tresses. Next, we explore the effect of conditioner (Pantene PRO-V Daily Moisture Renewal) on bleached hair. Table II shows the changes to friction and stiffness in response to the treat- ment. As expected, we observe dramatic decrease to the work of friction on pins (i.e. in- crease in lubricity) that becomes comparable to the work of friction of virgin hair (see Table I). The apparent stiffness has decreased along with the apparent friction coeffi cient. Similar to the exercise described in Table I, we pair two conditioned bleached hair tresses to illustrate once again that the apparent friction coeffi cient described is indeed indepen- dent of the hair amount in the tress. Finally, we illustrate the ability of the Aqualon SLT to detect changes in hair stiffness. In this experiment, washed hair tresses were treated with 0.25 gram of texturizing gel (DEP) followed by either air drying or blow drying while combing. Note that the amount and the mode of application of the gel was judicious in producing a realistic stiffening effect. Figure 5 shows images of both air and blow dried tresses. In the case of the air dried sample (Figure 5A), the treatment ‘glues’ hair fi bers together and repetitive deformation is expected to disrupt the fi ber-to-fi ber attachment points there- fore decreasing the apparent stiffness of the hair tress. Table III illustrates how these changes can be quantifi ed by the Aqualon SLT. Note that the measurements were Table II Impact of Conditioner Treatment on Bleached Hair Stiffness (g-force mm) Friction on pins (g-force mm) Friction coeffi cient No conditioner 1340 ± 100 2230 ± 200 1.7 ± 0.2 Conditioner 1140 ± 110 960 ± 140 0.8 ± 0.1 2 Conditioned combined 2760 ± 170 2390 ± 170 0.9 ± 0.1 Figure 5. Virgin tress treated with texturizing gel. (A) air dried. (B) blow dried tresses.