IMAGING OF PETROLEUM ASPHALTENES USING SCANNING-TUNNELING-MICROSCOPY

Scanning tunneling microscopy (STM) was used to image Ratawi (neutral zone) asphaltenes deposited on highly oriented pyrolytic graphite (HOP G). STM images revealed the formation of ordered arrays covering hundr eds of angstroms of the surface. Samples deposited from pyridine solut ions above and below the critical micelle concentration were quite sim ilar. The individual features imaged in these arrays were attributed t o the termini of the pendant aliphatic chains known to be a part of th e asphaltene molecular structure. The ordered arrays imaged were extre mely 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 as phaltenes to self-associate.