472 JOURNAL OF COSMETIC SCIENCE Figure 18. Ionic dye reaction to damaged hair. Structure-property relationships are important factors to consider in the process of either choosing or designing ingredients to test for hair repair. One has to theorize how the ingredient will interact with the fine structure and chemistry of hair in order to deter- mine if it is a candidate for experimentation. A few experiments have been shown in this paper that provides evidence that there are changes in the morphology and chemistry of hair during the damage process. One thing that is essential therefore in the repair process is that the ingredient has to have a cationic nature in order to bind to the anionic hair surface of the split fibers. Also, adhesive effects are necessary that are able to glue the split subassemblies of the fibers together. Lastly and most importantly the composition needs to be able to close the split ends and smooth the lifted cuticle scales so as to ensure a durable mend especially after combing or other stress factors during for example hair styling. Considering the chemistry and morphology of the microgel structure and its interaction with the chemistry and morphology of damaged hair, it seems reasonable that the polyelectrolyte complex is able to meet all of these criteria for the hair repair process. Based on this thinking a mechanism of action for the semi-permanent split end mending effect is proposed. Proposed mechanism of split end mending with PEC microgel. It has been shown that maxi- mum mending was achieved from microgels that were formed from polyelectrolyte complexes made from combinations of oppositely charged polymers close to a one to one stoichiometric charge ratio. This charge ratio was shown through viscosity measure- ments to be the point of maximum complexation. It is believed that although this charge ratio is balanced there exists in the microgel residual anionic and cationic charges that

2006 TRI/PRINCETON CONFERENCE 473 have not associated together. This is because of the steric hindrance that prevents the two macromolecules to completely associate all of their unlike charges together for complete neutralization. There are various aspects to the proposed mechanism of action of the hair repair process with the polyelectrolyte complex. First, the residual cationic charges on the microgel would tend to bind to the anionic sites of the damaged cortex through electrostatic association. To show the cationicity of the complex the anionic dye, Direct Red 80, was used as an indicator. Figure 19 shows a split end before treatment with the complex, after treatment showing mending, and after treatment with Red 80 showing a positive response to the dye. The higher level of red towards the tip indicates the predominance of complex. The red mark just prior to the split end again is the mark made with a permanent marker. During the drying stage the microgel complex is able to form a crosslinking structure which bridges the subassemblies of the fiber together. The microgel structure and its interaction with hair are illustrated in Figure 20A. The crosslinking adhesive structure of the microgel serves to glue the damaged parts of the fiber together. Since the complex is in the form of microgels in the size range of 5-10 microns they are small enough to infiltrate the fissures of the split cortex especially those as can be seen macroscopically as a split end. The smaller particles can to a certain extent permeate the lifted cuticle which is also present in damaged hair. After drying the microgels form a clear durable film which tends to bind these damaged parts of the hair together as is illustrated in A) Before treatment B) After treatment _1 ..... ..-.-.....-iiiiiiiici,iiidliiilr - C) After treatment plus Red 80 Figure 19. Anionic Direct Red 80 dye test indicates more microgel deposition on tip end.