Langmuir Technique and Brewster Angle Microscope Studies of the Interfacial Behavior of Bitumens, Asphaltenes, and Maltenes at the Air-Water Interface. 2. Variable Spreading Solution Concentration Effect

Efficient breaking of water-in-bitumen emulsions that cause undesirable effects in the petrochemical and oil sands industries requires a complete knowledge of the interfacial properties of bitumen and the surface active materials of which it is composed (asphaltenes and maltenes). In this work, the capability of bitumens, asphaltenes, and maltenes to form monolayers at the air−water interface and the structural conformations formed under different compression stages and constant added volumes taken from different concentration spreading solutions are analyzed using a Langmuir trough and Brewster angle microscopy. The results presented here support the conclusions extracted from previous studies and bring new light regarding the origin of the formed aggregates. In this way, the results confirm that, independent of the amount of added surfactant, the three fractions arrange in association structures, forming true monolayers at the air−water interface at low spreading solution concentrations. Out-of-plane regions were only verified for asphaltenes before compression, for high spreading solution concentrations, or at high surface pressures, for low concentrations. The area per molecule of the different association structures noticeably depends upon the spreading solution concentration. Decreasing concentrations lead to increasing areas per molecule. Therefore, aggregates with different degrees of aggregation can form at both the air−water interface and the bulk spreading solution.