POLYMER- SURFACTANT INTERACTIONS 221 7O 6O 5O 72 62 52 i i I 0.01 0.1 I % Polymer 4O 3O 5 4 3 2 1 -Log [SDS] Figure 5. Surface tension of the systems SDS/AADD at pH 9.5. O, SDS alone. AADD concentration: O, 0.01%. U1, 0.1%. A, 1%. Inset: O, surface tension of AADD alone in water. different from those obtained with other nonionic polymers such as polyethelene oxides (13,15) and polyvinyl alcohol (11). In these cases, at a fixed polymer concentration and with an increasing amount of SDS, two breaks in the surface tension curve are observed. The first break occurs at a concentration of SDS that is below its cmc, while the second break occurs at the surfactant concentration that is above the cmc. The surface tension of the second break is lower than that of the first one, with a value equal to that at the cmc of SDS. The first break represents the concentration of SDS at which the polymer/

222 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 7O 6O 5O o 62 52 0.01 0,1 1 % Polymer 4O I I I I 30 5 4 3 2 1 -Log [SDS] Figure 6. Surface tension of the systems SDS/AADD at pH 11.5. O, SDS alone. AADD concentration: (,.•, 0.01%. [q, 0.1%. Inset: O, surface tension of AADD alone in water. surfactant association begins, and the second break represents the concentration at which the polymer becomes saturated with surfactant. Here the associations are basi- cally driven by hydrophobic group interactions. However, in the AADD/SDS case the observed decrease in surface tension may be considered to be due to both hydrophobic interaction and a significant dipole-ion type of association between the dipole of the amine in the polymer and the ionic head in the SDS. All the mixed systems investigated at this pH were found to be clear. Viscosity measurements ideally would yield information on the association and confor- mation of the polymer-surfactant complex. But, because of the type of precipitate