The adsorption of Octadecyltrimemmonuim chloride (C
18 TAC)/Sodium-N-lauroyl-N-metyl-β-alanine (NaLMA) mixed system on keratin powder which was used as substitute for human hair was studied. The adsorption isotherm of C
18 TAC showed irreversible adsorption, resulting in the decrease of the kinetic frictional coefficient compared to other cationic surfactants (C
10TAC, C
12TAC, C
14TAC, C
16TAC). The adsorption istherm of NaLMA was of the Langmuirtype, but those of C
18TAC/MaLMA mixed system showed irreversible adsorption owing to strong interaction with keratin powder. The amount of adsorption was maximum at molar ratio 7/3 of C
18TAC/NaLMA. At the same ratio, the kinetic frictional coefficient and denaturation rate showed minimum values. That the behavior of C
18TAC/NaLMA mixed system is similar to nonionic surfactant aqueous solution and that the monomer concentrations of C
18TAC having the strong interaction decrease by formation of ionic pair between C
18TAC and MaLMA may suffice as explanation for the above results.
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