NMR Characterization of Elastomer−Carbon Black Interactions

Abstract

Here we report the application of two-dimensional NMR double quantum filtered correlation spectroscopy to characterize the interactions between components in biphasic, heterogeneous media. The method was applied to model systems of carbon black reinforced rubber. The presence of filler particles induces local susceptibility fields while a local partial ordering of the elastomer at the surface prevents the complete averaging of the dipolar interaction. The separation of susceptibility and dipolar interactions allows for the direct observation of three elastomer components near the surface of filler particles: (1) encapsulated, (2) ordered surface layer, and (3) unordered layer near the surface. The NMR method permits one to quantify the amounts of elastomer in each of these regions and to estimate the thickness of the surface component. The method is applied to study several rubber samples for which the carbon black particle size distributions were determined from scanning electron microscopy measurements. For these samples the length scale of the surface elastomer component is estimated, and it is shown that the encapsulated elastomer is most probably located between the graphitic plates of the filler particles rather than in the space between adjacent particles.