The interfacial behavior of asphaltene samples, obtained from two different sources, was studied by means
of Langmuir balance and Brewster angle microscopy (BAM) at the air/water interface. Transferred films from
the air/water interface on mica were studied by atomic force microscopy (AFM). Isotherms obtained from the
Langmuir balance experiments for all samples are qualitatively similar and indicate that their interfacial behavior
may be correlated to the molecular weight of the asphaltene samples. At mesoscopic scales, BAM images of
asphaltene films deposited on the water surface reveal that asphaltene samples do not form a monomolecular
film, as proposed in the literature, but rather a mixture of 2D and 3D domains. This behavior is confirmed
when, on a hydrophilic surface such as mica, the film is transferred from the Langmuir trough and is found
to be not homogeneous or monomolecular. AFM images revealed the formation of an irregular and meandering
layer of 10.2−12.5 nm thickness. Initially, the films exhibit some mesostructures graphically identified as
small and large disklike structures; these disks coalesce or fuse into more complex mesostructures: drumsticklike
and ribbonlike structures. A closer look revealed that these mesostructures are formed by small colloidal-like
particles or small micelles (<100 nm). The spreading capacity of asphaltene on the mica surface seems to be
related to the separation methods and the amount of resins associated with the asphaltenes. The complete
coverage of the surface and the formation of an irregular 3D film occur as a function of aging time or when
the transference pressure of the asphaltene film from water to mica is increased.
Undesired material adhered to the internal surface of the tubing wall of some petroleum wells is critical for crude oil production. Field samples of steel with petroleum solid adherence were characterized by means of x-ray photoelectron spectroscopy, x-ray diffraction and atomic absorption spectroscopy. The deposit naturally adhered on the steel surface is structurally formed by a thin, black and hard corrosion product layer (inner layer) ∼15 µm thick under a thick, black and brittle organic deposit layer (outer layer) ∼0.01 m thick composed mainly of hydrocarbons. This outer layer contains small amounts of barium sulphate (BaSO 4 ) co-precipitated with organic compounds, which may contribute to the deposit's lack of cohesion. On the contrary, the inner layer of the deposit is firmly adhered to the steel substrate and contains clay minerals and iron compounds embedded in the hydrocarbon layer.
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