j. Soc. Cosmet. Chem., 45, 135-148 (May/June 1994) A preliminary investigation of the interaction of a quat with silicones and its conditioning benefits on hair SHRENIK NANAVATI and ANNETTE HAMI, Dow Corning Corporation, 2200 W. Salzburg Road, Midland, MI 48686-0994. Received January 28, 1994. Synopsis Silicones, especially dimethicone and dimethiconol of higher molecular weights, have gained acceptance as conditioning agents and are used in several commercial products, frequently in conjunction with quats. In this work, the conditioning benefits of the silicones, as assessed by improvement in wet and dry combing, were investigated as a function of molecular weight as well as amount deposited on bleached hair. In addition, the combing performance of a quat was evaluated for the purpose of comparison, and its influence on the silicones, as pertaining to deposition and combing performance, was assessed. All the silicones improved wet and dry combing performance substantially over untreated hair. Their performance was greater than that of the quat for wet combing but was comparable for dry combing. The higher molecular weight gums showed slightly improved dry combing performance over the lower molec- ular weight fluids, but there was no significant difference between them for wet combing. Presence of the quat increased the amount of silicone depositing on the hair. A synergistic effect of the two was seen in that a significantly greater wet combing performance was displayed than was observed for the silicone or the quat alone. This phenomenon occurred for all of the silicones tested and was not observed for dry combing performance. INTRODUCTION Hair conditioning products (along with hair cleansing products) are increasingly being used on a daily basis. Whereas a shampoo is simply used to clean hair, a conditioner is used with a variety of expectations. These expectations encompass a large number of attributes, most of which are closely related to Robbins et al.'s definition of the term "hair manageability" (1). An attribute that is closely associated with conditioning is ease of combing, and an instrumental technique has been established to obtain a quantitative measure of this parameter (2). The isoelectric point of untreated hair is at pH 3.7 (3). This indicates that the hair surface attains a cationic charge at a pH under 3.7 while assuming an anionic character above that pH. Traditionally, quaternary ammonium salts (or quats) have been used as the main addititive responsible for conditioning effects. Their structure can be repre- sented as [N + (R)a(CH3) 4_ a]X-, where R is a long chain alkyl group, X is the counter anion, and a is the number of alkyl groups attached to the quaternary nitrogen atom. 135

136 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Quats have been found to be efficient at depositing on hair as well as improving its combability. The adsorption has been attributed to an electrostatic attraction between the anionic character of the hair fiber and the positively charged quat molecule (4-6). Hair has been described as being a "strong-acid ion exchanger," and one can expect some desorption of the quat upon rinsing with detergents (6). In addition to electrostatic forces, attraction owing to Van der Waals forces has also been shown to play a part in the adsorption process (7). Increasing the number of alkyl groups, as well as increasing the length of the carbon chains on the quat, has been shown to be beneficial for the conditioning of hair (8,9). If the cationic charge character is responsible for bringing the quat to the hair surface, it is the long-chain alkyl groups that are believed to be responsible for lubricity and combing performance (9). Though quats occupy a prominent position in the list of conditioning additives, other materials have been investigated for a variety of reasons. Out of these, polydimethyl- siloxanes (PDMS, silicones, siloxanes) have been identified as effective hair conditioning aids and are currently being used, frequently in conjunction with quats, in many commercial products. Because of their ease of spreading and thin film formation, along with their lubricity and emollient properties, silicones impart unique "feel" character- istics to personal care products and have gained industry-wide acceptance (10, ! 1). Silicones are also finding favor in conditioning shampoos (12). Silicones are homopolymers consisting of repeating units of dimethylsilicon bonded to oxygen, and their structure can be written as Y-O-{Si(CH3)20}x-Y. Depending on the end group, they are known as dimethicone (Y - Si[CH3]3) or dimethiconol (Y = H). As discussed above, both quats and silicones are known to condition hair. However, the influence of one on the other, as pertaining to conditioning, has not been well docu- mented. In this work, the combing benefits of silicones are assessed as a function of the amount of silicone deposited (as delivered from a solvent) as well as of the molecular weight of the silicone used. In addition, the interaction of a quat with the silicones and the resulting effect on deposition and combing performance is investigated. It should be noted that the results discussed below represent performances obtained from a solution. The deposition levels and other characteristics obtained from aqueous hair conditioning products may differ from these findings. EXPERIMENTAL MATERIALS AND GENERAL PROCEDURES Hair samples. All tresses were prepared with 2 grams of slightly bleached human virgin European hair, purchased from DeMeo Brothers, New York. The tresses were prewashed with a 15 wt% aqueous solution of ammonium lauryl sulfate (Henkel Corporation), rinsed, and dried. The tresses were then dipped individually into chloroform for a period of 40 seconds, and the resulting tresses were considered "untreated tresses." Treatment samples. Tricetylmonium chloride (Varisoft TC-90 ©, named quat for the pur- pose of this paper) was kindly supplied by Sherex Corporation, whereas all the polydi- methylsiloxanes {three dimethicone fluids--molecular weights of 10,000, 40,000, and 64,000, named fluids 1, 2 and 3, respectively two dimethiconol gums--molecular