AbstractThe effect of treatment temperature on the deposition and substantivity of surfactants and polymers on the surface of human hair has been investigated by measuring the surface wettability of the fiber with water before and after treatment. Advancing wettabilities indicate that the adsorption of low molecular weight cationic surfactants on the negatively charged hair surface goes through a maximum as treatment temperature is increased. This suggests an increase in the extent of chemisorption with increase in temperature, the decrease in wettability beyond the maximum being due, apparently, to orientation of the surfactant lipid chain toward the water making the surface more hydrophobic and less wettable. The adsorption and substantivity of anionic surfactants are low, due to the repulsion of negative charges on the hair surface. As with cationic surfactants, the adsorption of cationic polymers increases with treatment temperature, suggesting an increase in adsorption site activation. Increase in treatment temperature also increases polymer substantivity due to a lower probability of desorption resulting from multiplicity of attachments to sites on the fiber surface. Oxidation of the hair fiber surface, which involves disulfide cleavage to produce charged sites, leads to an increase in the extent of surface coverage and substantivity especially at lower treatment temperatures; reduction, on the other hand, does not result in significant increases. In those cases where desorption of deposited material does not affect the surface tension of the measuring liquid drastically, wettability data can be used to determine an average surface coverage if the contact angle of the liquid on the pure treatment material is known.
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