Viscoelasticity of poly(ethylene glycol) in aqueous solutions of potassium sulfate: a comparison of quartz crystal microbalance with conventional methods

The viscoelasticity of poly(ethylene glycol) (PEG) in aqueous solutions with different concentrations of potassium sulfate (K 2 SO 4 ) was studied by quartz crystal microbalance with dissipation (QCM-D), after coating a rigid supported lipid bilayer of 1,2-dioleoyl- sn -glycero-3-phosphocholine on the silicon oxide substrate. The obtained viscoelastic properties of PEG in K 2 SO 4 solutions agree well with the Zimm model predictions for linear polymer chains. With increasing K 2 SO 4 concentration, the excluded volume exponent ν of PEG decreased from 0.565 in water to 0.55 in 0.19 mol/L K 2 SO 4 , and 0.50 in 0.43 mol/L K 2 SO 4 . The solvent quality gradually worsened for PEG with increasing K 2 SO 4 concentration, which was verified by decreases in the polymer intrinsic viscosity and the corresponding Mark–Houwink exponent. The high-frequency characteristic of QCM-D makes it possible to directly study the viscoelasticity of polymer solutions in a low-viscosity solvent, which is complementary to conventional rheometers working at low frequency. Viscoelasticity of PEG in aqueous solutions containing different concentrations of K 2 SO 4 was studied by QCM-D, after coating a rigid supported lipid bilayer on the silicon oxide substrate. The obtained viscoelastic properties of PEG in K 2 SO 4 solutions agree well with the Zimm model predictions for linear polymer chains. The gradual worsening of solvent quality by adding K 2 SO 4 to aqueous PEG solutions is demonstrated by the obtained excluded volume exponents via QCM-D and the conventional intrinsic viscosity measurements.