Investigating the viscoelastic behavior of partially hydrolyzed polyacrylamide/polyethylenimine mixtures
Abstract
In this paper, the viscoelastic behavior of a polyethylenimine (PEI) crosslinked polymer gel prepared with a low hydrolysis/high molecular weight hydrolyzed polyacrylamide (PHPA), is investigated through dynamic shear measurements. The gel samples were cured at 80 °C while the rheological measurements were operated in a parallel-plate geometry at 25 °C. The effect of various parameters namely the reactants concentrations, the polymer’s molecular weight, the curing temperature, the presence of inorganic salts and the solution’s initial pH, on the storage (G’) and loss (G”) moduli were systematically investigated through frequency sweep tests. As a result, the final gel strength (G’ = 69.5 Pa) of a typical PHPA/PEI formulation was lower than those of the PAtBA/PEI and PAM/PEI systems reported in literature. Both storage (G’) and loss (G”) moduli varied proportionally and following exponential relationships with polymer concentration, crosslinker concentration, polymer’s molecular weight and temperature but unproportionally with the presence of inorganic salts (NaCl and CaCl2). On the other side, the effect of the gelant solution’s initial pH on the final gel strength was variable, with stronger gels formed around pH≈10, which was related to the asymmetrical effect of the pH on the two reactants (PHPA and PEI).