Rheology of Hydrophobically Midified Polyacrylamide in Water
Shu Hui, Robert A.
RMIT
Australia
Keywords: rheology , Solution, Polyacrylamide
Hydrophobically modified hydrophilic polymers are used as thickeners for aqueous solutions. The hydrophobes can associate to form a transient network, and this kind of network is easily broken by applying shear. Due to their unique rheological properties, hydrophobically modified polymers have been applied to paints and oil recovery. Commercialised thickeners include HEUR (hydrophobic ethoxylate urethane) and HASE (hydrophobic alkali-soluble emulsion). Polyacrylamide (PAM) is a water-soluble polymer that has unique solution properties after N-alkylation, for example the N-isopropyl derivative exhibits a lower critical solution temperature.
In this study, PAM has been hydrophobically modified by N-alkylation to provide varying hydrophobicity. The rheological properties of modified PAM, in water solutions, has been studied using steady shear and dynamic conditions. Increasing the hydrophobic chain length increased the steady shear viscosity of semi-concentrated solutions and increased the ratio of the elastic to viscous component of the dynamic viscoelastic properties. Analysis of the rheological data has been performed to measure the storage and loss shear modulus crossover frequency, and the data has been tested for deviation from the Cox-Merz rule. The results are interpreted in terms of polymer concentration, conformation and hydrophobic interactions.