Solution and interfacial behavior of hydrophobically modified water-soluble block copolymers of acrylamide and N-phenethylacrylamide

Hydrophobically modified water-soluble block copolymers were prepared by aq ueous micellar copolymerization of acrylamide and small amounts (2 and 3 mo l %) of a hydrophobe (N-phenethylacrylamide) that is characterized by a lon g spacer that places the aromatic ring far away from the backbone, with the objective of investigating the copolymers' rheological behavior and surfac e and interfacial activities under various conditions such as polymer conce ntration, shear rate, temperature, and salinity. As expected, the block cop olymers exhibit improved thickening properties attributed to intermolecular hydrophobic associations as the solution viscosity of the copolymers incre ases sharply with increasing polymer concentration. Additional evidence for intermolecular association is provided by the effect of NaCl, the presence of which substantially enhances the viscosity. An almost shear rate-indepe ndent viscosity (Newtonian plateau) is also exhibited at high shear rate an d a typical non-Newtonian shear thinning behavior appears at low shear rate s and high temperatures. Furthermore, the block copolymers exhibit high air -liquid surface and liquid-liquid interfacial activities as the surface and interfacial tensions decrease with increasing polymer concentration, indic ating strong adsorption of the copolymer at the interface. The surface and interfacial tensions exhibited by the copolymers were found to be relativel y insensitive to the concentration of salt (NaCl). (C) 2001 John Wiley & So ns, Inc.