SMALL-ANGLE NEUTRON-SCATTERING BY PARTIALLY DEUTERATED POLYMERS AND THEIR BLENDS

Partially deuterated polymers, made by saturating the double bonds of polydienes with deuterium, have been found to produce weak but signifi cant coherent patterns in small-angle neutron scattering (SANS) experi ments: The results suggest the presence of slight differences in deute ration levels among the chains. The scattering profiles for such mater ials and for blends containing them were calculated with the multicomp onent random phase approximation (RPA). The coherent intensity for the deuterated component alone is predicted to be proportional to the var iance of its Scattering length distribution and to have a q dependence corresponding to the pure component structure factor. The SANS data f or a variety of partially deuterated polyolefins are shown to be consi stent with these predictions. The theory also predicts that the scatte ring from their blends with an hydrogenous component is enhanced by th is scattering length inhomogeneity, that the enhancement is additive, and that the conventional two component RPA may be used to analyze the data after this contribution is subtracted. Experimentally, we find t hat uncorrected scattering from blends rich in such deuterated compone nts lead to anomalous estimates of chain dimensions and thermodynamic interactions. The anomalies disappear when the proposed correction is applied.