Surface Rheological Properties of Hydrophobically Modified Polyacrylamide and Imidazolium Surfactant Systems

The dilational rheological properties of hydrophobically modified polyacrylamide (HMPAM) or hydrolyzed polyacrylamide (HPAM) solutions without and with imidazolium surfactants ([C14-4-C14im]Br2 and [C14mim]Br) at the air/water surface were investigated using oscillating bubble measurements. The results obtained suggest that imidazolium surfactants interact with the polymer on the surface, enhancing the dilational viscoelasticity of surface film. The dilational modulus value of [C14-4-C14im]Br2/HMPAM is higher than that of the [C14mim]Br/HMPAM system at low polymer concentration, confirming that [C14-4-C14im]Br2 with two head groups and two hydrophobic chains can combine with a polymer to form a strong film on the surface. Moreover, imidazolium surfactants have stronger hydrophobic interaction with HMPAM chains than those of HPAM, thus enhancing the surface film strength for a surfactant/HMPAM system. The surface interaction mechanism between polyacrylamide and imidazolium surfactant is proposed to result from the electrostatic interactions and the hydrophobic effect.