LIGHT SCATTERING THEORY TO MEASURE RINSABILITY OF HAIR CONDITIONERS 399 In this experiment, four simple conditioning systems were studied (refer to Table I): one based on a behenyl quat, a second based on di-behenyl quat, a third based on an amine salt as the conditioning active, and the fourth using a non-ionic emulsifi er as the negative control system. The rinsing behaviors of the four conditioners were evaluated using two different hair types, namely European bleached and European virgin hair, enabling us to study the surface interactions between the hair types and the conditioner systems. In this study, three hair tresses were used per hair type for each conditioner treatment. Each tress was individually cleansed with a basic shampoo then rinsed. Following cleans- ing, each tress was treated with 2 g of the respective conditioner treatment, and then subjected to an automated rinsing system. The rinsed water was collected every 5 s, start- ing at 0 s. The Turbiscan was used to measure each sample to obtain a transmittance value. A calibration curve was subsequently established for each conditioner system to determine an equation of the line, which would then be used in later analysis to correlate optical density to concentration. To establish the rinsability curve, each curve was nor- malized and initialized starting at 0 s. Each subsequent point is a percentage decrease in concentration with respect to the initial point to determine how much conditioner is left on the hair with respect to the initial amount of product applied to each hair tress (2 g). Concentration is presented in terms of percentage and is graphed as a function of rinsing time in seconds. RESULTS AND DISCUSSION Figure 1 depicts the calibration curves for the four conditioners. All conditioners exhib- ited a linear correlation between concentration and optical density. The variation in the slopes can be attributed to the solubility of the conditioner products in water. It is ob- served that the absorbance value of the rinsed solution mainly depends on the degree of transparency of the solution, or the turbidity. The more turbid the solution, the higher the absorbance value. Therefore, absorbance can be used as an indicator of the solubility of the tested conditioner in water. As a result, the slope of the calibration line is an indica- tion of changes in solubility of the conditioner with concentration. The calibration curves will serve as a basis for the rinsability of the conditioners. Table I Con ditioning Formulations Ingredients Conditioner A: behenyl quat (%) Conditioner B: di-behenyl quat (%) Conditioner C: amine salt (%) Conditioner D: non-ionic emulsifi er (%) Part A D.I. Water Q.S. Q.S. Q.S. Q.S. Part B Conditioning active 1.50 1.50 1.50 1.50 Fatty alcohol 4.50 4.50 4.50 4.50 Part C Preservative 0.10 0.10 0.10 0.10 All formulations based on 1.5% active conditioning active in the systems and neutralized to pH 4.0–4.5.

JOURNAL OF COSMETIC SCIENCE 400 RINSABILITY PROFILE OF VARIOUS CONDITIONERS The data on the rinsability profi le of the different conditioners on bleached hair is depicted in Figure 2. One can observe that Conditioner A, based on the behenyl quat, washes off the hair quickly initially, but then plateaus the quickest compared with the other condi- tioning systems, indicating that more residual product remains on the hair. This can be attributed to the cationic nature of this material and its long alkyl chain and substantiv- ity to the negatively charged surface of the bleached damaged hair. Contrary to Condi- tioner A, Conditioner B, based on the di-behenyl quat, rinsed out more slowly with much less residual product remaining after 30 s of rinsing. Conditioner C, based on the amine salt, took the longest to rinse out overall of all the conditioners. We can hypothesize that Figur e 1. Calibration curves for Conditioner Systems of with Different Chemistries. Figure 2. The Rinsing Behavior of Conditioner Systems on European Bleached Hair as a Function of Time.