Viscoelastic properties of poly(ethylene oxide) solution

The viscoelastic properties of poly(ethylene oxide) (PEO) solution were investigated using the dynamic oscillatory testing technique. With this technique, the effect of PEO molecular weight (MW), concentration, composition of mixed solvent systems consisting of propylene glycol, glycerol formal, and water, and the effect of NaCl salt on the viscoelastic properties of PEO solution were determined. Dynamic moduli (G1, G2), magnitude of complex viscosity (magnitude of eta*), and loss tangent (tan delta) were examined over a frequency range of 10(-3)-2.5 Hz at 30 degrees C. The results indicated that low MW PEOs show liquidlike behavior while high elasticity is exhibited by high MW PEOs due to entanglement formation. The complex viscosity, magnitude of eta*, exhibits shear thinning (power-law) characteristics under oscillatory measurements. The relationship between steady shear and complex viscosities follows the Cox-Merz rule over the shear rate and frequency region studied. Both the storage (G1) and loss (G2) modulus increase drastically as the proportion of water in the mixed solvent system increases. Similarly, both G1 and G2 are found to increase while the tan delta decreases with increasing concentration of PEOs. The addition of up to 2% w/w NaCl in an aqueous solution of 10% w/w 2 million MW PEO has no observed detrimental effect on the viscoelastic behavior.