Large amplitude oscillatory shear rheology for nonlinear viscoelasticity in hectorite suspensions containing poly(ethylene glycol)

The effect of poly(ethylene glycol) (PEG) on the nonlinear viscoelasticity of Laponite suspensions containing NaCl was investigated with large amplitude oscillatory shear rheology. The molecular weight (M_w) of PEG was 4k, 10k and 35k, and the concentration of PEG was varied from 0.063 wt% to 2.4 wt%. The dynamic strain sweep showed that the nonlinearity appeared at γ₀ > 30% with a stress overshoot at γ₀ = 50-70%. The intensity ratio I_3/1 from Fourier-transform increased with γ₀ when entering the nonlinear regime and leveled off at γ₀ ≥ 100% with higher slope and constant value for the PEG of higher M_w or lower concentration. I_3/1 revealed the structure difference in the suspensions induced by adsorbing PEG in the nonlinear regime. The minimum- and large-strain rate viscosities η_M and η_L from the Lissajous curve were found to be sensitive to the nonlinear viscoelasticity and the peak of η_M and η_L appeared at lower γ₀ with higher maximum following the same dependency as I_3/1 on PEG M_w and concentration. The overall nonlinearity parameters N_E and N_V were proposed in this paper and demonstrated to reflect the difference in the Laponite suspensions with PEG more clearly and more effectively.