Interactions between hydrophobically modified polymers and surfactants

Abstract

The rheological behavior of mixtures containing hydrophobically modified poly(sodium acrylate) (HMPAA) and surfactants is studied. The hydrophobic groups of the polymer (octadecyl or dodecyl chains) interact with the surfactant molecules to form mixed micellar-type aggregates. In semidilute solution these mixed aggregates act as cross-linkers between the polymer chains, inducing a viscosification or gelation of the system. The strongest effect was observed with a cationic surfactant, because in this case both electrostatic attraction and hydrophobic interactions contribute to the stabilization of the mixed aggregate. However, association occurs even between HMPAA and an anionic surfactant (SDS), despite the unfavorable electrostatic repulsions, indicating that the hydrophobic interactions are the driving force for the formation of the mixed aggregates.