MORPHOLOGY OF COMPLEX AGGREGATES IN SHAMPOOS 299 Figure 12. Rheologcal parameters, G′, G″, and η∗, of precipitated complexes from ten-times-diluted solu- tions. (a) Model shampoo containing CC at α=0.38 and LES (b) model shampoo containing CC at α=0.21 and LES/LPB=3/1. Figure 13. Touch of hair in the rinsing process of model shampoo solution. formed mesh-like aggregates, showed a smooth touch. This suggested the large contribu- tion of the rheological properties of the precipitated complexes to the touch upon rinsing. Moreover, the complex with lower charges in a dispersed state (CC at α = 0.21 and LES/LPB=5/5) gave a somewhat oily touch. Surfactants adhering to hair with the com- plexes caused an oily touch because the rheological properties of the complexes were lower. In contrast, the touch upon rinsing was smooth for CD at α = 0.38 and LES/LPB=3/1 (Figure 4a), even though the membranous morphology was close to that of CC at α=0.38 and LES (Figure 6a). The rheological properties of the precipitated complexes for CD at α = 0.38 and LES/LPB=3/1 were similar to those in Figure 12b (the data are not shown here). This suggests that the differences in the fl exibility of the polymer chains in coil-like
JOURNAL OF COSMETIC SCIENCE 300 complexes determine the rheological properties and the touch upon rinsing, even though the morphologies of the precipitated complexes are the same. Practically, the touch in the rinsing process corresponds to the wet feel after shampoo- ing. Other conditioning agents in shampoos, like silicon, and in a conditioners have greater effects on the feel after drying. The membranous morphology in the complexes of CC led to a stiff feel after drying when much of the complex adhered to the hair. To realize a good dry feel, the control of morphology in the complexes and the adjustment of synergism between the precipitated complexes and other conditioning agents would be important. CONCLUSIONS The CP region in the phase diagrams that contained cationic cellulose (CC) or dextran (CD) and added anionic surfactant and the relative scattered intensity of solubilized com- plexes have been observed. The relationship between the morphology of the complexes precipitated by dilution of the model shampoo solution and the touch on hair has been studied, and the effects of the charges of the polymer and added surfactant and the struc- ture of the polymer chain have been discussed. CC molecules with rigid chains are favorable for rod-like complex conformation. It is considered that the rod-like complexes cross-linked and coacervated in the dilution pro- cess of the model shampoo solution. The complex aggregates precipitated from the model shampoo solution had a membranous morphology if both the CC and surfactant were highly charged a mesh-like structure with openings was created and the aggregates were loosened when both charges were reduced. This suggested that the cross-links in the complex aggregates were reduced with decreasing charge and showed no precipitation if the charge of the polymer was low (for instance, if α = 0.1). In contrast, CD molecules with fl exible chains are favorable for contracted coil-like complexes. No complex precipitated when the anionic charge on the surfactant was high, and the complexes precipitated if the anionic charge of the surfactant was re- duced. CD led to membranous complex aggregates in the model shampoo solution even when the charges of the polymer and surfactant were lower. This suggested that the rod-like CC molecules and contracted coil-like CD molecules form different mor- phologies of complex aggregates, depending on the charge and structure of the poly- mer chains. The touch of hair in the rinsing of the model shampoo with CC refl ected the rheological properties that corresponded to the morphology of the precipitated complexes. The CC complex aggregates gave a smooth touch when they showed a loose mesh-like morphol- ogy. In contrast, CD complex aggregates gave a smooth touch even though they exhibited a membranous morphology, probably because of the fl exibility of the CD polymer. These results suggested that the control of the charges of both the polymer and surfactant and of the choice of the polymer structure is important for excellent effects in the rinsing of shampoo. Moreover, silicone and other oils are mixed in shampoos nowadays. Thus, the complex aggregates involve these agents when they precipitate from the shampoo solu- tion. The morphology of complex aggregates in this work would closely relate to the deposition of silicone. The control on the morphology of complex aggregates is important for excellent conditioning effects.
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