Imaging of Petroleum Asphaltenes Using Scanning Tunneling Microscopy

Abstract

Scanning tunneling microscopy (STM) was used to image Ratawi (neutral zone) asphaltenes deposited on highly oriented pyrolytic graphite (HOPG). STM images revealed the formation of ordered arrays covering hundreds of angstroms of the surface. Samples deposited from pyridine solutions above and below the critical micelle concentration were quite similar. The individual features imaged in these arrays were attributed to the termini of the pendant aliphatic chains known to be a part of the asphaltene molecular structure. The ordered arrays imaged were extremely flat and uniform, in contrast to the assumed molecular complexity and the absence of unique structure of asphaltenes. The formation of these ordered surface arrays is further evidence of the tendency of asphaltenes to self-associate.

STM Investigation of Pyridine Interaction with Heteropoly Acid Monolayers

“…Even though the scan sizes of the STM images presented in this report are less than 100 Å (in order to emphasize resolution), the ordered arrays extended well beyond the typical scan range of 300 Å. The periodicity of the arrays of H 3 PMo 12 O 40 in the STM image of Figure 2a is 10.77 ( 0.26 Å and is in excellent agreement with dimensions determined by X-ray crystallography 30-32 and by STM. 16 The periodicity of the arrays of Cs 3 PMo 12 O 40 is 13.68 ( 0.14 Å, somewhat larger than that of H 3 PMo 12 O 40 .…”

Self-Association of Asphaltenes

“…Similarly, the scanning tunneling microscopy is simple and accurate. However, the sample pretreatment is needed to insure good experimental data [82]. (3) the phase separation process as a function of pressure, temperature and solvent quality, as presented in the viscosity section in this chapter.…”

Bituminous emulsions and their characterization by atomic force microscopy

“…The colloidal structure of bitumen has been reported in the literature (Donnet et al, 1973;Loeber et al, 1996Loeber et al, , 1998, and imaging of the asphaltenes of the bitumen by some authors (Dickie et al, 1969;Mercier et al, 1994;Watson et al, 1994;Zajac et al, 1994Zajac et al, , 1997Bardon et al, 1996). Basu & Sharma (1997) measured the interacting forces for the different crude oil compounds with a substrate using AFM.…”

“…Analysis of the molecular and atomic structure of bitumen or its asphaltenes in dilute conditions by atomic force microscopy (AFM) or nuclear magnetic resonance is now possible (Dickie et al, 1969;Watson & Barteau, 1994;Zajac et al, 1994;Zajac et al, 1997). However, it is difficult to relate the basic molecular structure to the colloidal behaviour and threedimensional organization of the bitumen, which can reach more than 100 nm by aggregation of smaller species and by network formation (Donnet et al, 1973;Bardon et al, 1996;Loeber et al, 1998).…”