Rheological characterization of poly(ethylene oxide) solutions of different molecular weights

The rheological properties of aqueous solutions of poly(ethylene oxide) (PEO) of different molecular weights (1 x 10(5), 4 x 10(5), 1 x 10(6) and 4 x 10(6) g mol(-1)) and concentrations were investigated using shear viscosity and dynamic rheological measurements. It was found that the aqueous solutions of PEO do not exhibit a yield stress and that, above a critical shear rate, all PEO solutions exhibit shear-thinning behavior, well described by the Cross model, except for the solutions made by the lowest molecular weight (1 x 10(5) g mol(-1)) which were almost Newtonian. The parameters of the Cross model, namely the zero-shear rate viscosity and reciprocal of the time constant, allowed the determination of the critical concentrations c* and c** (respectively, the transition to semi-dilute network solution and concentrated solution). At concentrations higher than c** and below a critical shear rate, solutions made of PEO of high molecular weight exhibited a clearly shear-thickening behavior at very low shear rates. In addition, the dynamic tests showed that PEO solutions exhibit concentration-dependent viscoelastic properties, with a dominant viscous behavior at PEO concentrations lower than c** and a dominant elastic behavior at PEO concentrations greater than C**. (C) 2009 Elsevier Inc. All rights reserved.