NMR measurement of the alignment tensor for a polymer melt under strong shearing flow

H-2 NMR quadrupole interaction spectroscopy has been used to measure the deformation of a 610 kD PDMS melt under shear in a Couette cell. The signals were acquired from a perdeuterated benzene probe molecule, which provides a motionally averaged sampling of the entire segmental ensemble. Our Rheo-NMR method involves the use of a selective storage precursor pulse, which enables one to observe NMR spectra from preselected regions within the flow. We have measured the dependence on the shear rate of the S-XX (velocity) and S-YY (velocity gradient) elements of the segmental alignment tensor as well as the angular dependence of the deuterium quadrupole splitting at a fixed shear rate. The results agree well with Doi-Edwards theory and return a value for the tube disengagement; time of 310 ms.