INVESTIGATION OF STRESS DISTRIBUTIONS IN FILLED POLYSILOXANE BY NMR IMAGING

NMR imaging is applied to industrial poly(dimethylsiloxane). Samples were investigated in the strained and unstrained state with and without a cut, and compared with two model compounds. Inhomogeneous filler distributions cause variations in the magnetic susceptibility and lead to contrast in gradient-echo images. T2-parameter images revealed distributions in segmental mobility associated with the filler inhomogeneities as well as with the cut. The images were recalibrated to give strain and stress images by use of integral stress and T2 values determined for macroscopic uniaxial strain. The effects of filler inhomogeneities appear larger in the NMR images than in polarization micrographs because of magnification by magnetic field distortions from susceptibility differences in gradient-echo images, and because changes in segmental mobility of surrounding polymer chains are detected rather than the filler itself. The methods can also be applied to 3D imaging of nontransparent rubbers.