Characterization of Adsorbed Athabasca Asphaltene Films at Solvent-Water Interfaces Using a Langmuir Interfacial Trough

Characteristics of adsorbed monolayers of fractionated high molecular weight, low molecular weight, and unfractionated whole asphaltenes at a heptol (a mixture of heptane and toluene)-water interface have been studied with a Langmuir interfacial trough. The deposited monolayer Langmuir-Blodgett (LB) asphaltene films were characterized with atomic force microscopy (AFM), contact angle measurements, and Fourier transform infrared spectroscopy (FTIR). Monolayers of the three asphaltene samples behave similarly at a heptol-water interface, as characterized by close resemblance of the corresponding pressure-area, hysteresis, and relaxation isotherms. For pressure-area isotherms, a monolayer of the low molecular weight asphaltene is the most expanded, while a monolayer of the high molecular weight asphaltene is the most condensed. In terms of relaxation characteristics, a monolayer of the high molecular weight asphaltene relaxes most quickly. Similarity among the three asphaltene samples is further evidenced by close resemblance of topographies of AFM images, contact angle values, and FTIR spectra of the deposited LB asphaltene films. In general, an asphaltene monolayer is more flexible at a heptol-water interface than at an air-water interface.