Chapter 3 93 rinsing. The first two-in-one shampoos depended on a complex coacervate being formed between anionic surfactant and the cationic hydroxyethylcellulose,polyquaternium 10. This complex was solubilized in excess surfactant and it phase-separated as a coacervate liquid phase upon dilution during the rinsing cycle. Later guarhydroxypropyltrimonium chloride was introduced as an alternative cationic polymer that worked on the same principle as polyquaternium-10. These two polymer types continue to dominate the compositions of conditioning shampoos.40 Guar is a galactomannan and it is interesting that, in recent years, recently a new cationic galactomannan hydrocolloid, cationic cassia, has been claimed to confer conditioning shampoo benefits.41,42 Polygalactomannans consist of a polymannan backbone with galactose side groups. In guar gum, there is a pendant galactose side group for every two mannan backbone units. These galactose groups sterically hinder the substitutable C-6 hydroxyl unit and this limits the extent of possible cationic substitution on guar gum. In cassia, however, there is less steric hindrance of the C-6 hydroxyl group and, consequently, higher degrees of cationic substitution are possible with cassia (60% for cassia relative to 30% for guar). Cationic cassia can be used as a conditioning polymer in shampoos and conditioners to impart cleansing, wet-detangling, dry-detangling and manageability. The mechanism of conditioning shampoos depends upon the formation of polymer/surfactant coacervates that phase-separate during rinsing (see Figure 16). Polyions in aqueous solution are surrounded by an electrical double-layer of counterions and the location of the counterions with respect to the polyion is determined by a balance between chemical potential and electrochemical potential, called the Donnan Equilibrium. Surfactant ions contain a large hydrophobic group and this makes them intrinsically less soluble in water than inorganic ions such as chloride or bromide. When surfactant ions interact with an oppositely charged polyion, they bind strongly and displace the water-soluble inorganic ions from the polyion that is, they ion-exchange. Once the surfactant