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

2H 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 SXX (velocity) and SYY (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.