Rheology of a xanthan broth at low stresses and strains

The structure of a concentrated (4·7 wt %) xanthan broth was probed by dynamic oscillatory, steady shear, and stress-relaxation tests on denatured, renatured, and native xanthan solutions. The range of the shear rates extended down to 10^-5 s^-1 to test for the existence of a yield stress. Though the viscosities at these very low shear rates were extremely high for polymer solutions (10⁵ Pa. s), no evidence of a true yield stress was found. Long range order was indicated by a difference in complex and steady shear viscosity, presumably arising from inter-chain hydrogen bonding and liquid crystal formation. Differences in recoverable strain between the various samples arise from dissimilar structures and long range interactions in the solutions.