Langmuir films of bitumen and its fractions extracted from oil shales (Puertollano, spain)

Interfacial properties of bitumen (extracted from Spanish oil shales), asphaltene, and maltene monolayers at the air-water interface are studied by means of the Langmuir technique. The results obtained in this work reveal the formation of aggregation structures of asphaltenes and maltenes at the air-water interface previous to compression. Upon compression, asphaltenes form condensed monolayers while maltenes show an expanded state at low specific areas due to the formation of an overfilm. The presence of maltenes in bitumen hampers the formation of large aggregates of asphaltenes, allowing for the existence of a liquid expanded phase in bitumen films. The maltenes present the highest compressibility of the three compounds favoring the coalescence of the emulsion droplets, while asphaltene films, displaying the lowest compressibility, form rigid films that avoid coalescence. Bitumen, asphaltene, and maltene films are lost when compressed at 20 mN/m initially by rearrangement and/or formation of association structures and later by dissolution into the subphase.