Nonlinear viscoelastic rheology of sodium alginate and cellulose nanofiber hydrogels under large amplitude oscillatory shear
The single-component and the composite of alginate and cellulose nanofiber hydrogels have been characterized by linear and nonlinear rheology. In this study, large amplitude oscillatory shear tests at varying fixed angular frequencies of 3.14 rad/s, 6.28 rad/s, and 9.42 rad/s were employed to characterize the samples. We found that the hydrogels showed similar linear viscoelastic properties, but differed in nonlinear viscoelastic properties. Hydrogels of the composites, alginate, and 5.0 wt% conc. of cellulose exhibited weak strain overshoot behaviour, while 0.66 wt% conc. of cellulose hydrogel exhibited strain thinning behaviour. At increasing strain amplitudes, the nonlinearity of the elastic G' and viscous G'' moduli of the hydrogels became evident with an increase in the phase angle, reflected by a sinusoidal stress response with time, elliptical Bowditch-Lissajous curves, and the high frequency end of the Fourier harmonics of these moduli. Our results imply that porosity may play an important role in structural stability at high deformation. Thus, dilute nanofiber inclusion might contribute to high strain stability by introducing porosity.