Asphaltene Monolayers at a Toluene/Water Interface

Asphaltene films at a toluene/water interface were characterized using a Langmuir interfacial trough. An asphaltene monolayer was determined to remain at the toluene/water interface, and asphaltenes do not migrate from the monolayer to the bulk toluene or water phase. When the hydrocarbon phase is removed and replaced with a fresh toluene phase (dilution experiment), the pressure−area isotherm obtained was almost identical to that from the original asphaltene monolayer at the interface. Addition of 2-propanol into the oil phase (toluene) caused the interfacial asphaltene monolayer to become more flexible. However, 2-propanol molecules did not displace asphaltene molecules. Atomic force microscopy (AFM) images of the transferred Langmuir−Blodgett (LB) asphaltene films from toluene−water and a mixture of toluene and 2-propanol/water interface show similar aggregated structures. Fourier transform infrared (FTIR) spectra of the deposited LB asphaltene films show the presence of bonded water in asphaltene films.