Solution behavior of hydrophobically associating water-soluble block copolymers of acrylamide and N-benzylacrylamide

Hydrophobically modified water-soluble block copolymers have been prepared by an aqueous micellar copolymerization technique from acrylamide and small amounts of N-benzylacrylamide (2 and 3 mol%) with the objective of investigating the copolymers' rheological behavior and surface and interfacial activities under various conditions such as polymer concentration, shear rate, temperature and salinity. As expected, the block copolymers exhibit improved thickening properties due to intermolecular hydrophobic associations as the solution viscosity of the copolymers increases sharply with increasing polymer concentration. Additional evidence for intermolecular association is provided by the effect of NaCl salt on the solution viscosity, and as expected, the addition of NaCl to the polymer solution gives rise to copolymers with enhanced thickening properties. An almost shear rate independent viscosity (Newtonian plateau) is also exhibited at high shear rate and a typical non-Newtonian shear thinning behavior appears at low shear rates and high temperatures. Furthermore, the block copolymers exhibit high air-liquid surface and liquid-liquid interfacial activities as the surface and interfacial tensions (IFTs) decrease with increasing polymer concentration. This behavior is yet another evidence of polymolecular micelles formation of the copolymers in aqueous solution, and thus the high tendency to adsorb at an interface. The surface and IFTs exhibited by the copolymers were found to be relatively insensitive to the concentration of salt (NaCl).