Overhauser Effect in Asphalt Solutions

Abstract

We have discovered that solutions of asphalt in a suitable solvent will show an Overhauser effect. The effect is qualitatively similar to that in crude oil. It arises from a dipolar interaction between the unpaired spins in the asphaltic free radicals, and the protons of the solvent molecules. The contribution to proton relaxation from the asphalt is a linear function of asphalt concentration. The function relating proton signal enhancement to electron saturating rf field strength is found to vary with asphalt concentration. A plot of enhancement versus electron‐stimulating frequency at constant H 0 yields a curve similar to the EPR absorption line. The large size of the asphalt radicals does not appear to have any direct significance with respect to the Overhauser interaction.