Effect of additives on the structural organization of asphaltene aggregates in bitumen

Bitumens are composite materials whose complex organization hinders the rational understanding of their relationships between composition, structure and performances. So, research attempting to shed more light in this field is required. In this work Wide Angle X ray Scattering (WAXS) has been used to explore the influence of six opportunely chosen additives on the bitumen structure with the aim to ultimately correlate the findings with the bitumen performances. Diagnostic fingerprints have been observed in the WAXS profile: asphaltenes form stuck of about 18 Å and constituted by about 6 asphaltene units on average. Such stucks are, in turn, organized at higher levels of complexity forming anisotropic aggregates of about 200 Å × 28 Å which, again, are assembled to form micrometer-size elongated aggregates characterized by the so-called bee-structure. The structural effects of the six opportunely chosen additives (Organosilane, Polyphosphoric, Phospholipids, Acetamidophenol, Oleic Acid, octadecylamine) have been pointed out and, corroborated by AFM images, have been correlated with the rheological behavior and justified at the microscopic level: additive with an apolar nature are preferentially located in the maltene phase weakening asphaltene inter-clusters interactions and softening the bitumen, whereas, on the contrary more polar additives act in opposite directions. Peculiar behavior have been unveiled in the case of amphiphilic additive due to the simultaneous presence, within their molecular architecture, of both polar and apolar moieties. The knowledge of the detailed effect of appropriately chosen additives on the nanoscopic and mesoscopic structure and their correlation with the rheological properties constitute the first step for opening the door to the piloted design of new bitumens with desired properties for ad-hoc uses.