Interfacial Thermodynamic Properties of Films Containing Crude Oil Amphiphiles

This work describes the interfacial behavior of films containing petroleum amphiphiles by evaluating their surface thermodynamic properties. It aims to contribute to studies of petroleum stability by describing the thermodynamics and rheological behavior. The experimental methodology includes extraction and characterization of the oil fractions (SARA fractions) and analysis of the rheological properties of the surface films through hysteresis tests using the Langmuir Trough. A thermodynamic approach was applied to determine the Gibbs surface energy of mixtures containing asphaltene and resin over a full concentration range. Experimental results obtained from surface compression–expansion isotherms show that asphaltene films display the most substantial effect on the air–water surface properties. The behavior of the resin film in the hysteresis process indicates a high interaction between the molecules, leading to a sharp surface pressure drop during expansion, so that the film cannot return to its initial state. In addition, the saturated film dissipated less energy in the hysteresis cycle than the other films, which is related to its weaker molecular interaction. The maximum elasticity modulus was obtained for the asphaltene–resin mixtures for the asphaltene composition x = 0.4. The excess areas obtained for the asphaltene–resin mixtures indicate that the molecular interactions are most repulsive in the compression process and that the molecular interactions are strongly attractive during the expansion process. The Gibbs energy of the mixture is reduced by increasing the asphaltene content, especially for films formed under high pressure. Gibbs energy for expanding films remains approximately constant with the changes in asphaltene concentration. It is worth noting that the results point out the occurrence of intense interaction between asphaltene molecules during film formation under compression.