The Fast Relaxation Process between Hydrophobically Modified Associating Polyacrylamide and Different Surfactants at the Water‐Octane Interface

Abstract

In our previous work (Macromolecules 2004, 37:2930), we found that the hydrophobic blocks of polyacrylamide modified with 2‐phenoxylethyl acrylate (POEA) and anionic surfactant sodium dodecyl sulfate (SDS) may form mixed associations at octane/water interface. However, the process involving the exchange of surfactant molecules between monomers and mixed associations in interface is so fast that we cannot obtain its characteristic time. In this article, the interfacial dilational viscoelastic properties of another hydrophobically associating block copolymer composed of acrylamide (AM) and a low amount of 2‐ethylhexyl acrylate (EHA) (<1.0 mol%) at the octane‐water interfaces were investigated by means of oscillating barriers method and interfacial tension relaxation method respectively. The influences of anionic surfactant SDS and nonionic surfactant Triton X‐100 on the dilational viscoelastic properties of 7000 ppm polymer solutions were studied. The results showed that the interaction between P(AM/2‐EHA) and SDS was similar to that of P(AM/POEA) and SDS. Moreover, we got the relaxation characteristic time of the fast process involving the exchange of s Triton X‐100 molecules between monomers and mixed associations. We also found that the interfacial tension response of hydrophobically associating water‐soluble copolymers to the sinusoidal oscillation of interfacial area at low bulk concentration is as same as that of the typical surfactants: the interfacial tension decreases with the decrease of interfacial area because of the increase of interfacial active components. However, the interfacial tension increases with the decrease of interfacial area at 7000 ppm P(AM/2‐EHA), which is believed to be correlative with the structure of absorbed film. The results of another hydrophobically associating polymer P(AM/POEA) and polyelectrolyte polystyrene sulfonate (PSS) enhanced our supposition. The phase difference between area oscillation and tension oscillation has also been discussed considering the apparent negative value.