NMR FLOW IMAGING OF AQUEOUS POLYSACCHARIDE SOLUTIONS

Nuclear-magnetic-resonance (NMR) flow imaging with spatial resolution of the order of 200 mu m is used to measure the velocity fields in aqu eous solutions of 0.2% and 1% xanthan gum and 1% guar gum for steady f low in a 1.2 cm internal diameter cylindrical polymethylmethacrylate p ipe. The velocity fields show little evidence of apparent wall slip an d are differentiated to obtain relationships between shear stress and shear rate which span over four decades in shear rate for the xanthan solutions and approximately three decades for the guar solution; these data agree well with those obtained by cone-and-plate viscometry. The behavior of the xanthan solutions is well described by a power-law de pendence of shear stress on shear rate, and the guar solution is bette r described by a Cross-type relationship. The implications of these st udies for future NMR flow imaging studies of more complex systems are discussed.