(447g) Adsorption Of Asphaltenic Aggregates On Monolayers Of Alkyl And Phenyl Silanes

We report preparation of pure and mixed monolayers of alkyl and phenyl tricholorosilanes on silicon substrates which we have characterized by their wetting behavior with contact angle goniometry, by ellipsometry to judge the thickness of the organic thin films, and by near-edge x-ray absorption fine structure spectroscopy (NEXAFS) to assess the ordering of the chains and the relative concentration of phenyl and alkyl moities. These substrates then served as adsorption templates for nanoscale molecular aggregates of petroleum asphaltenes, which are known to contain fused ring aromatic cores and aliphatic pendant groups. The adsorption of the asphaltenes was characterized by ellipsometry and NEXAFS. We have determined that, with sufficiently long alkyl chains, the asphaltenes do not adsorb onto the substrate to any appreciable degree. We have also explored the role of polar functional groups in the pure and mixed monolayers as well as the role of alkyl chain length. The results have implications for surface modification in sub-sea pipelines as preventive measures to avoid asphaltene deposition. The results can also be used to design chromatographic substrates for fractionating asphaltenes chemically.