JOURNAL OF COSMETIC SCIENCE 262 (i) The contact materials are hair. (ii) The technique operates in a force range, which is relevant to the hair assembly. (iii) In spite of the fact that the technique involves very low load (10 μN) and a very small contact area, multiple slides along the hair length allow probing the distribution of interaction forces along the hair fi ber length (cm). In this work, the objective was to exploit the incline plane fi ber loop method to deter- mine hair fi ber–fi ber interactions induced by silicones, focusing in particular on under- standing the properties of block copolymer silicones versus the traditional straight PDMS polymer. PDMS polymers are known to be very fl exible and mobile, whereas the hydro- philic polar blocks of copolymer silicones interact with the hair substrate, restraining the mobility of the silicone segments. An additional objective was the identifi cation of links between the hair fi ber–fi ber interaction measurements and the macroscopic behavior of hair assembly. The changes of volume and shape of curly hair tresses at high humidity were observed to determine whether the presence of silicones increased fi ber-fi ber interac- tions, reducing the frizziness of curly hair at high humidity. EXPERIMENTAL INCLINE PLANE FIBER LOOP APPARATUS AND PROCEDURE An incline plane fi ber loop method apparatus, adapted from Robbins and Howell and Mazur, was created for the quantifi cation of the hair fi ber–fi ber interactions. A schematic of the apparatus is shown in Figure 1. The apparatus was enclosed in an environmental chamber at 25°C and 50% RH. A single hair loop, of diameter 3.8 cm, slid on two paral- lel hair fi bers (L = 10 cm). The two parallel fi bers were mounted on an aluminum plate that was attached to a preci- sion motorized rotary stage. The rotary stage (CZ7) from Thorlabs was controlled by a DC servo controller that was interfaced with a PC. Each parallel fi ber was mounted at each end by a brass fl at clamp from Diastron, A nylon thread with a closed loop connected to the hair fi ber allowed the tension of the hair fi ber to be adjusted, using standard Figure 1. Incline plane hair loop apparatus.

2008 TRI/PRINCETON CONFERENCE 263 weight. In all experiments, the tension was adjusted with a 10 g weight, unless indicated otherwise. There was a directional effect of the fi ber on this hair loop friction measure- ment sliding was consistently performed from root to tip of the hair fi ber. The parallel fi ber plane was tilted at a constant rotation speed of 2°/s, until it slid, or fell. The operator stopped the rotary stage when the loop started sliding or falling, and the angle was re- corded by the motor driver software. The hair loops were formed on a cylinder of 3.8 cm diameter, using very thin tape strip to close the loop. Additional thin tape strips were mounted on the loop to act as counter- weight. Using that procedure, the total hair loop weight was approximately 2 mg. For each treatment, 15 fi bers were chosen randomly from a hair tress, to make 5 loops and 5 pairs of parallel fi bers. The fi bers were kept in the environmental chamber overnight prior to measurement. For a given loop and parallel fi ber pair, 10 “slides” were performed, to probe the hair fi ber–fi ber interactions at different positions along the fi bers. 50 slides were performed by treatment. SILICONE MATERIALS Four of Momentive’s silicone polymers were used for the hair treatments. Silsoft* 1215 dimethiconol gum is a very-high-molecular-weight linear PDMS terminated by hydroxyl groups. The quat silicone, INCI name silicone polyquaternium 18, is a very high molecular weight block copolymers containing polyether group, amino quat group and silicone chain as described in (4). Silsoft A-843 copolymer, INCI name Bisamino PEG/PPG-41/3 aminoethyl PG-propyl dimethicone, is a block copolymer with an (AB)n structure, alternat- ing polyether segments and silicone chain. The SME 253 aminosilicone is a linear silicone with pendant amigo groups. For simplifi cation, in the following sections, silicone poly- quaternium 18, Silsoft A-843 copolymer, SME 253, and dimethiconol gum will be called respectively silicone quat, amino ABn, aminosilicone and silicone gum. The neat poly- mers of amino Abn and aminosilicone were dissolved in isopropanol. The silicone quat and the dimethiconol gum were dissolved in cyclodimethicone (D4). HAIR TREATMENT PROTOCOL Virgin brown hair and brown curly hair were purchased from Hair International Hair Importers. Some curly tresses were relaxed using a commercial relaxer to make the loops. Bleaching was performed using a aqueous solution of 1.35% ammonium hydroxide and 3% hydrogen peroxide at pH = 10. The hair tress was dipped for 30 minutes in a fresh bath and then rinsed for 2 minutes in tap water. Four successive bleaching treatments were performed in this study. To apply a controlled amount of silicone to the hair, 1.4 g of solvent was applied to each 2-g tress, which was dried fl at overnight at 50°C. HAIR SURFACE DAMAGE ASSESSMENT The hair surface damage level achieved by the processes described in the previous section was assessed using a wicking test. The hair tress was held taut by two paper clamps on a glass slide. A droplet of DI water was deposited on the fl at taut hair tress and the time for *Silsoft is a trademark of Momentive Performance Materials Inc. Copyright 2008 Momentive Performance Materials Inc. All rights reserved.