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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