Interfacial behaviour of asphaltenes in oil/water systems

In this work, the hanging drop tensiometry technique was used to better describe the interfacial rheological properties of asphaltenes, extracted from two Brazilian oils, at the toluene/water and heptol (heptane+toluene)/water interfaces, varying the proportions of organic solvents in 1:1 and 1.5:1 and the concentration of asphaltenes. Adsorption isotherms and Gibbs and Langmuir equations of state were investigated. For systems containing toluene as solvent, the attraction between solvent molecules and asphaltene molecules is strong due to its high solubility, thus reducing the interfacial activity of asphaltene molecules. For systems containing heptol as a solvent, the interaction between the asphaltene molecule and the solvent molecules is weak, resulting in an increase in the interfacial activity of the asphaltene molecules. The dilatational rheological interfacial properties of the systems studied (IFT, surface pressure and modulus of elasticity) depend exclusively on the interfacial coverage. These results are useful for understanding how asphaltene adsorption processes occur at fluid/fluid interfaces at the microscopic level.