Rheological behaviors and molecular motions of semi-diluted Xanthan solutions under shear: Experimental studies

Semi-diluted Xanthan solution has been widely used in various fields, especially in enhancing oil recovery. The oscillatory shear and flow shear behaviors of Xanthan are important to oil flooding. The oscillatory shear relates to molecular motions, while flow shear reflects flowing characterization. In oscillatory shear mode, the storage modulus, loss modulus and tanδ has been measured. Calculating relaxation spectra through storage modulus, we found that the peak of segments’ relaxation heads to smaller relaxation time side. Also, the quantity of relaxation units increases as concentration increases. However, the relaxation time spectra are less affected by salinity. In flow shear mode, the relationship between shear rate and viscosity has been investigated. As concentration or salinity increases, the pseudoplastic of Xanthan solutions becomes more obvious. Furthermore, primary normal stress differences of Xanthan semi-diluted solutions lightly increase at first then sharply decrease as shear rate increases. This abnormal phenomenon may refer to wall slip.