Chain Deformation for a Polymer Melt under Shear

We used a Couette cell placed within an NMR microscopy apparatus to examine molecular alignment in polydimethylsiloxane melts under shear. 1H dipolar interactions are used to examine main chain ordering while 2H NMR quadrupole splittings are measured in a deuterated oligomer probe, in each case selectively observing different alignment orientations with respect to the flow field. While the main chain results are consistent with the alignment tensor as measured by birefringence, the oligomer senses a uniaxial environment whose director is normal to the velocity-vorticity plane. In the light of these results we propose supramolecular ordering involving polymer stratification. [S0031-9007(98)07618-2]