Effects of concentration and NaCl on rheological behaviors of konjac glucomannan solution under large amplitude oscillatory shear (LAOS)

The linear and nonlinear rheological properties of konjac glucomannan solutions as affected by its concentration and the addition of sodium chloride were investigated by both small and large amplitude oscillatory shear tests (SAOS/LAOS). This study has identified that the apparent viscosity, storage modulus, and loss modulus of konjac glucomannan solutions increased significantly by increasing its concentration but reduced dramatically by adding sodium chloride. Shear thinning was observed in all konjac glucomannan concentrations with or without sodium chloride. Besides, sodium chloride delayed the critical shear rate at which shear thinning appeared and reduced the viscosity dependency. Notably, both the conversion from “soft gel” to “hard gel” and the appearance of secondary loops (Lissajous curves) were captured by increasing konjac glucomannan concentration. Chebyshev coefficients illustrated that all konjac glucomannan solutions transformed from shear thickening to shear thinning behavior. Thick konjac glucomannan solutions (0.8%, 1.0%) exhibited strain stiffening, while thin solutions (<0.8%) experienced strain softening under large deformations. The findings of this research provide insights for the diversified nonlinear rheological behaviors of konjac glucomannan solutions induced by its concentration and sodium chloride, which will prove useful in expanding our understanding of konjac glucomannan for its further application.