J. Cosmet. Sci., 62, 179–189 (March/April 2011) 179 A study of the distribution of polymer/surfactant coacervate between solution and foam in archetypal shampoo systems LEIGH ANN WILGUS, KATHLEEN DAVIS, LAUREN LaBEAUD, LISA GANDOLFI, and ROBERT Y. LOCHHEAD, School of Polymers and High Performance Materials, University of Southern Mississippi, Hattiesburg, MS 39406. Synopsis The research reported here attempted to answer the question, “is the foam important in delivering coacer- vates from shampoos.” In order to answer this question, we have measured the amount of polymer in the foam and in the liquid phases of several cationic polymer/anionic surfactant systems by gravimetry and by FTIR techniques. In all cases studied, we discovered that the concentration of solids and, especially the polymer, in the liquid phase and in the foam phase were essentially the same. We conclude that the foam is unlikely to be an important factor in the topical delivery of polymer/surfactant coacervates. INTRODUCTION Two-in-one shampoos commonly depend upon triggered complex coacervation to deposit materials on the hair. The general mechanism that underpins these stimuli-responsive sys- tems is known: the coacervate is solubilized at shampoo concentrations but separates as a liquid phase when the shampoo composition is diluted during rinsing. The coacervate de- posits on the hair to confer conditioning benefi ts and it can also act as a delivery system for the deposition of other components such as silicones or anti-dandruff ingredients. To date much of the study of coacervate deposition on hair has been focused on liquid systems. However, in the real application, the shampoo is foamed on hair prior to rinsing. This raises the question of the signifi cance of the surfactant foam on the delivery of co- acervate to the hair surface. This is a reasonable question because, in processes such as mineral froth fl otation, hydrophobic particles are readily separated from hydrophilic par- ticles and concentrated in the froth. In shampoos, lather is believed to give the consumer a perception of cleansing as they use the product. To achieve this rich lather, companies include surfactant concentrations greater than those needed to cleanse even the most soiled hair (1). In 2-in-1 shampoos, cationic polymers form complex coacervates that separate upon dilution and deposit on the hair and scalp surfaces to deliver components that confer attributes such as ease of combing and anti-dandruff properties. The question that we were trying to answer in this
JOURNAL OF COSMETIC SCIENCE 180 research was, “how important is the shampoo foam on the eventual deposition of the co- acervate?” The fi rst stage of this investigation, reported here, was to determine if coacer- vate was concentrated in the foam. CONDITIONING SHAMPOOS Conditioning is a term used in hair shampooing. Conventional Conditioners are usually based on cationic surfactants and alkanol co-surfactants. In the present case, however, conditioning is achieved by the triggered deposition of complex coacervates comprising cationic polymer and anionic surfactant. The conditioning polymer is used at relatively low levels usually less than 1% by weight is incorporated into the shampoo, which con- tains from about 10 to 20% anionic surfactant(s). Upon dilution with water, complex coacervate (formed from the cationic polymer and anionic surfactant) separates from solu- tion as the shampoo is rinsed from the hair (2). The quaternary polymers investigated in this study were Polyquaternium-7, Polyquater- nium-10, Polyquaternium 76, and Polyquaternium-88, the chemical formulae of which Figure 1. Structures of cationic polymers used in this study.
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