JOURNAL OF COSMETIC SCIENCE 136 length and the force measured. “Suppleness” thus combines attributes of the hair friction on the tool, fi ber-fi ber friction and the fl exural stiffness of hair (6). Our own device, con- ceived and developed independently of this work, takes the approach a step further by allowing to separate the contributions of fi ber-fi ber friction and stiffness, referred to as apparent stiffness in this work, from the friction on the surface of the tool, defi ned as appar- ent lubricity. The design of the Aqualon SLT, measurement method, and the utility of stiffness and lubricity are described herein. AQUALON SLT DESIGN AND MATERIALS Figure 1 illustrates a prototype version of the Aqualon SLT* in the assembled state placed on a platform at the base of the Instron Tensile Tester. The plastic screw on the face of the device is used to switch between rotational (pins can freely rotate) and stationary (pins immobilized) modes of operation. The action of the screw is illustrated in Figure 2. The inside of the detached face plate shows attached rubber circles located, when assembled, opposite to the pins. When the face plate is engaged, the rubber circles push on the pins and immobilize them. Alternatively, when the screw is pulled out, the spring (also shown in the fi gure) acts to push the plate away from the pins thus allowing them to rotate freely. Pins are covered by tightly fi tting replaceable Tefl on sleeves. Figure 3 shows how the hair tress is threaded through the tool. Testing was carried out with Caucasian virgin and bleached hair tresses from International Hair Importers weigh- ing 3 grams and measuring 1 × 12 . The Aqualon SLT, however, can be readily adjusted *Patent pending. The Aqualon SLT device in its improved form can be obtained from Ashland Aqualon Performance Materials by contacting Abe Vaynberg at kvaynberg@herc.com Figure 1. The Aqualon SLT placed on platform mounted on Instron Tensile Tester.

2008 TRI/PRINCETON CONFERENCE 137 to accommodate different hair assembly confi gurations. Prior to each set of pulls hair tresses were combed, treated with an anti-static device (Zerostat) and the weight of the tress zeroed on Instron prior to the measurement. The pulling was carried out at the speed of 1000 mm/min and the experiment repeated 3–4 times in both rotational and station- ary modes. Hair tresses were washed by wetting with 40°C running tap water, applying the treat- ment, lathering the tresses for 30 seconds and rinsing in running 40°C tap water for 30 seconds. This was followed by a fi nal rinse with room temperature DI water for 15 sec- onds. All hair tresses were blown dry using hand held hair dryer (Conair 1875) at warm heat and low air fl ow for ~3 minutes while combing, unless noted otherwise. AQUALON SLT MEASURED PARAMETERS The Aqualon SLT measures the rotational and stationary work of pulling. In the case of the rotational mode, the pins mounted on ball bearings are rotating freely. This elimi- nates the friction on the pins and the only contribution to the work of pulling (measured by Instron) is the resistance to deformation of an assembly of individual hair fi bers, hair- to-hair friction and friction in the bearings that is assumed to be negligible. We defi ne the combination of these two parameters as the apparent stiffness. In the stationary mode, the tress is subjected to the same deformation with pins immobi- lized and, in addition to the apparent stiffness, the friction on pins contributes to the work of pulling. Figure 4 shows force profi les produced by a Caucasian virgin hair tress in the two modes. The two profi les follow an identical pattern with the force profi le in stationary mode shifted upward by a proportionality factor related to the hair tress friction on the pins. Figure 2. The Aqualon SLT with the face plate dismantled, illustrating the operation in rotational and sta- tionary modes.