Polyelectrolyte‐micelle coacervation: effect of coacervate on the properties of shampoo

Abstract

A typical formula for shampoo containing cationic polymers and anionic/amphoteric surfactants exhibits liquid–liquid phase separation under certain conditions when the shampoo is diluted with water upon the actual use in bathroom. The lower dense phase is considered to be an insoluble complex formed with the cationic polymer and mixed surfactants. Generally, this associative liquid–liquid phase separation is called ‘coacervation’ and the phase of complex is called ‘coacervate’. Although it is well known that the usage texture of shampoo is influenced by coacervate, there are only a few reports about their relationship. In this work, we studied the properties of coacervate and its effect on the usage texture of shampoo, particularly focusing on the effect of the cationic polymer structure. We prepared five different model shampoos that contain various cationic polymers and studied the effect of the characteristics of the polymers on the condition of the complex formations, the amount of coacervate, the rheological properties and the adhesive behaviour of coacervate on the surface of damaged hair. It was found that both the structure and the degree of substitution of cationic polymer drastically changed the condition of coacervation. Moreover, the cationic polymers showed remarkable effect on the rheological properties and the adhesive behaviour of the coacervate on the damaged hair. These results implied that we could control the usage texture of shampoo by choosing proper cationic polymers to control coacervation.