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submitted on 23.10.2018 and posted on 24.10.2018by Yunlong Zhang, Bruno Schuler, Shadi Fatayer, Leo Gross, Michael R. Harper, J. Douglas Kushnerick
This study addresses the effect of sample preparation
conditions on the structural integrity and composition of heavy hydrocarbon
mixtures imaged by non-contact atomic force microscopy (nc-AFM). We designed
and prepared a set of organic molecules mimicking well-accepted key
characteristics of heavy oil asphaltenes including molecular architecture, molecular
weight, boiling point, atomic H/C ratio and bond strength. We deliberately
focused on multi-core molecule structures with long aliphatic linkers as this
architecture was largely absent in previous nc-AFM studies of petroleum
samples. The results confirm that all these molecules can be successfully imaged
and remain intact under the same preparation conditions. Moreover, comparison
with ultra-high resolution FT ICR-MS of a steam-cracked tar asphaltene sample
suggests that the single molecules identified by nc-AFM span the entire
molecule spectrum of the bulk sample. Overall, these results suggest that
petroleum molecules within the scope of chosen molecules studied herein can be
prepared intact and without bias and the imaged data can be representative.