Small Angle Neutron Scattering Studies of Asphaltic Materials

ABSTRACTAsphaltic materials are used as binders for road asphalts. Such materials have been found to contain a dispersed phase of colloidal particles in the size range of 50-100 Å, according to small angle X-ray scattering(SAXS) techniques. The presence of this dispersed phase has a significant influence on the rheological properties of these materials. These colloidal particles can be isolated by precipitation with heptane, and so they are associated with the well-known asphaltene solubility class in some manner. In this work we review previously published results that suggest that at least part of the asphaltenes are surface active agents in certain solvents such as toluene, or pyridine, and can form micelles in these solvents. Small angle neutron scattering (SANS) indicates the micelles are spherical with average radii in the 50-100 Å range. There is a polydispersity of sizes. The micelles do not grow in these solvents with increasing concentration in the range of 1-10 wt.%, nor do they dissociate on heating to ~ 170 °C. At higher concentrations, however, a more complicated structure develops. The micelles aggregate to form a large cluster composed of micelles. The fractal dimension of the clusters is found to be 1.8.