Micellization of Anionic Sulfonate Gemini Surfactants and Their Interactions With Anionic Polyacrylamide

Anionic sulfonate gemini surfactants 8‐s‐8(SO₃)₂ and 12‐s‐12(SO₃)₂ (s = 3, 6) were synthesized, and their micellization in aqueous solution at 25.0 °C and pH 9 was investigated. The results show that the critical micelle concentrations (CMC) of 8‐s‐8(SO₃)₂ are more than 2 orders of magnitude larger than those of 12‐s‐12(SO₃)₂, but the spacer length has a relatively small impact on the CMC. Moreover, the interactions of n‐s‐n(SO₃)₂ (n = 8, 12; s = 3, 6) with anionic polyacrylamide (PAM) at 25.0 °C and pH 9 were investigated using surface tensiometry, rheolgy, and scanning electron microscopy (SEM). The results indicate that the surface tension and rheological properties of PAM depend on the concentration of n‐s‐n(SO₃)₂. Below the critical aggregation concentration of C₁, surface tension is sharply reduced, the surface tension of n‐s‐n(SO₃)₂/PAM is lower than n‐s‐n(SO₃)₂ alone, but viscosity is almost unchanged with increasing C_{n‐s‐n(SO3)2}. Above C₁, surface tension reduces very slowly until the saturated concentration of C₂ is reached. Above C₂, surface tension rapidly reduces until C_M is attained, suggesting free n‐s‐n(SO₃)₂ micelles begin to form. In the region of C₁–C_M, the viscosity significantly increases. Above C_M, surface tension is basically unchanged and these curves coincide with those of the single surfactant system. Moreover, the viscosity is almost constant. The SEM images indicate that fibrous aggregates are formed below C₁, then transformed into multilayer fibrous aggregates above C₁, and further into fiber‐braided‐structured and spider‐web‐structured aggregates above C_M. The variation of viscosity is closely associated with the transformation of aggregates.