Keratin biological substrates like hair are examples of natural hydrophobic surfaces. In both the membranes of the living cells that were at the origin of these evolved organs developed and structured forming an hydrophobic barrier against the more hydrophilic protein material. The hydrophobic interaction is sustainably prone to disappear after weathering or other hair and skin aggressions. Cosmetic ingredients try to restore these interaction proposing innovative solutions for hair and skin protection and repair.
We will present an updated review of our research on the understanding of the physical parameters affecting the adsorption of charged polymers on this kind of surfaces. By combining different surface science techniques (i.e. Quartz Crystal Mycrobalance or Atomic Force Microscopy) we can advance towards the identification of the properties of the substrates and to understand the way a specific cosmetic treatment (new active or material) alter them.
A particular challenging situation is the adsorption of zwitterionic polymers. Using Surface Plasmon Resonance (SPR) technique, we will present results of the adsorption of a functionalized natural polymer, in the presence or not of surfactants on a model surface for bleached hair. The polymer adsorbs 35-45% less in a neutral ionic state (PZ) than in a cationic state (PC). This slightest adsorption of the neutral polymer is at the origin of the higher fiction of hair and therefore a lack of smoothness and disentangling capacity. The deposition of the neutral polymer PZ in aqueous solution with 2 types of surfactants (simplex formula of a shampoo) is around 60-65% lower than the PC in presence of surfactants. By using two model surfaces, we concluded that the electrostatic interactions between the surface and the deposition are not only the possible interactions playing in this case.