n‑C7 Asphaltenes Characterization as Surfactants and Polar Oil from the HLDN Model Perspective

There is no consensus regarding the role of asphaltenes at the oil–water interface. In trying to solve this uncertainty, this work shows for the first time the n-C7 asphaltenes characterization as surfactants and polar oil based on the normalized hydrophilic–lipophilic deviation model (HLDN). Interfacial tension (IFT) and interfacial rheological properties of asphaltene/solvent/brine systems at equilibrium were determined. Additionally, stability and electrical conductivity measurements of emulsions obtained from those systems were performed. The results seem to indicate that when the asphaltenes concentration C A in the oil is equal to the critical nanoaggregate concentration (CNAC), the optimum formulation (HLDN = 0) of the system is reached. When C A < CNAC (HLDN < 0), the asphaltenes molecules behave similarly to a slightly hydrophilic nonionic surfactants, while when C A ≫ CNAC (HLDN > 0), asphaltenic clusters have a dual behavior as interfacially active lipophilic aggregates and polar oil.