Interaction of Lauryl Diethanolamide and Its Sodium Dodecylbenzene Sulfonate Composite With Hydrophobic Modified Polyacrylamide at Different Concentrations

ABSTRACT The rheology of hydrophobically modified polyacrylamide (HMHPAM) with lauryl diethanolamide (LDEA) and sodium dodecylbenzene sulfonate (SDBS)/LDEA surfactants was examined via steady shear and creep recovery, focusing on the plateau modulus ( G 0 ), relaxation time ( T R ), and zero‐shear viscosity ( η 0 ). For a 2000 mg/L HMHPAM solution (concentration between the critical association concentration, CAC, and critical entanglement concentration, CEC), the addition of LDEA enhanced and stabilized η 0 , G 0 , and T R , with a moderate increase in G 0 . In contrast, for a 4000 mg/L solution (above CEC), these parameters initially peaked and then decreased with increasing LDEA. A higher hydrophobicity of HMHPAM resulted in greater sensitivity of η 0 , G 0 , and T R to surfactant concentration. In the composite surfactant system at a fixed SDBS level, η 0 was predominantly governed by T R . The incorporation of SDBS markedly boosted η 0 , G 0 , and T R at low LDEA concentrations. While the SDBS concentration had a negligible effect on viscoelastic parameters in the 2000 mg/L system, it significantly enhanced η 0 and T R in the 4000 mg/L system, with a comparatively weaker impact on G 0 . These findings are interpreted within the framework of the transient network theory, elucidating dynamic changes in the solution's microstructure.