Insight into the Interaction Between Carbopol^sup ^ 940 and Ionic/Nonionic Surfactant

Mixtures of a cross-linked polyacrylic acid (Carbopol^sup ^ 940) and two types of surfactants, namely anionic sodium dodecylsulfate (SDS) and nonionic Tween^sup ^ 80, were investigated by viscometry, conductometry, tensiometry, spectrophotometry, fluorimetry and scanning electron microscopy (SEM). The addition of nonionic surfactant decreased the reduced viscosity and the transmittance of the Carbopol^sup ^ polymer aqueous solutions. Furthermore, the interaction between Carbopol^sup ^ 940 and SDS was characterized by two significant concentration values: the critical aggregation concentration of SDS was particularly independent of Carbopol^sup ^ polymer concentration while the polymer saturation point of both surfactants increased with the increase in polymer content. The values of critical aggregation concentration and polymer saturation point obtained using various techniques confirmed the occurrence of Carbopol^sup ^ polymer-surfactant associations. The effect of different SDS and Tween^sup ^ 80 concentrations on the conformation of Carbopol^sup ^ 940 in aqueous solution could be explained through hydrophobic association between surfactant micelles and Carbopol^sup ^ polymer tails and through hydrogen bonding in the case of Tween^sup ^ 80. Additionally, the surfactant-induced structural changes were confirmed in Carbopol^sup ^ 940-SDS and Carbopol^sup ^ 940-Tween^sup ^ 80 aqueous solutions by SEM measurements.