Surface wettability of human hair. III. Role of surfactants in the surface deposition of cationic polymers

Abstract

The effects of low molecular weight surfactants of different ionic characteristics on the deposition of a quaternized cellulosic polymer onto the surface of hair from solution have been studied. The uniformity of deposition and the substantivity of the deposited material has been assessed from measurements of the surface wettability of treated hair fibers with water. The results show that anionic surfactants at low-to-moderate concentrations bind with the cationic polymer so that the substantive layer deposited on the fiber surface tends to be hydrophobic due to orientation of lipid chains away from the surface. At high concentration, additional anionic surfactant molecules interact with the cationic polymer molecule by hydrophobic bonding, reducing the polymer–surfactant complex to an anionic polyelectrolyte which has little substantivity to the fiber surface. Cationic surfactants, on the other hand, do not interact with the polymer because of charge repulsion but compete with the polymer for negatively charged sorption sites on the surface, greatly reducing surface coverage by the polymer. The interaction of amphoteric surfactants with the polymer depends on the pH of the solution. Studies on experimental shampoos containing anionic and amphoteric surfactants confirmed these observations, and indicated, in addition, that dilution of the shampoo in the presence of hair plays a significant role in the deposition of the polymer on the hair surface.