Langmuir technique and Brewster angle microscope studies of the interfacial behavior of bitumen, asphaltenes and maltenes at the air–water interface. I. Effect of different spreading solution volumes

It is believed that surface active materials in bitumen (asphaltenes and maltenes) are responsible for the stabilization of undesirable water-in-bitumen emulsions in several processes in the petrochemical and oil sands industries. In order to find an efficient technique to break these emulsions, complete knowledge of the interfacial properties of bitumen, maltenes and asphaltenes is required. In this work, the capability of these three fractions to form monolayers at the air–water interface and the structural conformations formed under different compression stages and different added volumes, taken from constant concentration spreading solutions, are analyzed using a Langmuir trough and Brewster angle microscopy. According to the results presented here, the three fractions form true monolayers at the air–water interface with bitumen displaying a “sponge-like” structure, asphaltenes arranging in dense islands and maltenes forming very thin flexible layers. Bitumen, asphaltenes and maltenes organize in association structures of added volume depending sizes: increasing volumes lead to increasing sizes. Compression of the monolayers also favors the formation of larger structures that, upon expansion, do not relax to their original state. This fact is responsible for the hysteresis displayed by the three fractions, being asphaltenes the fraction showing the greatest rigidity, maltenes the greatest flexibility and bitumen an intermediate behavior. Out-of-plane regions were only detected for asphaltenes, which at high surface pressures, fold and bulge up, resulting in a loss of surface active material at the air–water interface. These three-dimensional structures persist upon expansion of the film.