Biaxial deformation of a polymer network measured via deuteron quadrupolar interactions

Deuterium quadrupolar interactions have been used to measure chain ordering for poly(dimethylsiloxane) elastomers under planar biaxial extension. The NMR spectral splittings obtained from two different deuterium-labeled probe molecules diffusing within the network were measured as a function of extension ratio and the orientation of the principal axis of deformation with respect to the magnetic field. Theoretical predictions based on a phantom Gaussian chain model are compared with the data and good agreement is found. The implications of axial asymmetry at various levels of the probe molecule motional hierarchy are discussed. For rapidly diffusing probe molecules, only the highest level in the hierarchy influences the observed quadrupole interaction symmetry, and the true distribution of chain segment directors is measured.