Rheology of xanthan solutions as a function of temperature, concentration and ionic strength

摘要

The rheology of renatured xanthan solutions was studied using oscillatory and continuous shear. The effects of temperature, concentration and ionic strength were systematically investigated. These parameters mainly influence the terminal relaxation time of the solutions, while the effect on the high frequency shear modulus is relatively minor. Master curves were obtained by frequency-temperature superposition covering over 10 decades of the frequency. Frequency-concentration superposition of the master curves showed that the shear rheology of xanthan solutions is universal. The relaxation time decreases with increasing temperature and shows a transition between two states that shifts to higher temperatures with increasing ionic strength. The relaxation time increases exponentially with increasing polysaccharide concentration. The shear rate dependence of the viscosity is also described by a universal function with the same shift factors as for the oscillatory shear measurements. The master curves show a Newtonian plateau followed by strong shear thinning that can be described by a power law dependence on the shear rate. The results are interpreted in terms of the formation of a transient network of chains cross-linked by bonds with a finite lifetime.