<SUP>2</SUP>H-NMR Imaging of Stress in Strained Elastomers

²H NMR was used to image stress in strained elastomer bands made from natural rubber. Deuterated poly(butadiene) oligomers were incorporated into the rubber network by swelling. They act as spy molecules for probing the local chain orientation. Under uniaxially applied stress, the chain motion becomes anisotropic and the deuterium resonance is split into a doublet. The quadrupole splitting was spatially detected in two ways. Spectroscopic 2D imaging was used to acquire a spectrum for each spatial position. From each spectrum the line splitting was extracted and recalibrated to stress. A similar result could be achieved by the analysis of double-quantum (DQ) filtered images. Here, the image contrast is determined by the amplitude of the DQ signal, the spin density, and relaxation effects. The influence of the last two can be removed to yield images in which the contrast is determined only by the strength of the DQ coherence which passes the DQ filter. The quadrupole splitting can be extracted from a set of such images, and subsequent recalibration also leads to stress images. The first method can easily be implemented and is experimentally robust, but it suffers from low sensitivity to small strains while strong signals from isotropic regions restrict the dynamic range of the measurement. The second method is very sensitive to small strains, but only qualitative information is obtained unless a whole set of differently filtered DQ images is evaluated.