Studying Structure-Nanoaggregation Relations of Polyaromatic Molecules in the Bulk Oil Phase and at the Oil-Water Interface Using Molecular Dynamics Simulation Open Access

[摘要] The detection, identification and characterization of early stage molecular association of polyaromatic molecules into nanoaggregates, where these nanoaggregates represent the first level of molecular clusters or building blocks are critical in areas such as design and fabrication of advanced 3-D materials, drug carriers, petroleum and crude bitumen processing, etc. Molecular association of polyaromatic molecules (e.g., asphaltenes) in petroleum and crude bitumen processing, for example, leads to precipitation and deposition, which results in blocking of reservoir rocks and transport pipes. The deposition of these polyaromatic molecules has been linked to the solubility, aggregation and colloidal interactions in the system. To probe the aggregation and adsorption mechanism of the polyaromatic molecules in an organic medium and at the oil-water interface, various well-designed and custom-synthesized perylene bisimide-based polyaromatic molecules with only a subtle structural difference in their attached hydrophilic/hydrophobic side chains were used and systematically investigated by molecular dynamics simulations. The results showed that variation in the structure of hydrophilic/hydrophobic side chains and polarity of functional groups leads to significant variations in molecular association, dynamics of molecular nanoaggregation and network formation of nanoaggregates. The aggregates of polyaromatic molecules grow to larger sizes in aliphatic than aromatic solvents. The aromatic solvent was shown to hinder molecular association by weakening pi-pi stacking, demonstrating the control of molecular aggregation by tuning solvent properties. Larger size aromatic rings in polyaromatic molecules lower the interfacial activity of the polyaromatic molecules due to stronger intermolecular pi–pi interactions and molecular aggregation in the bulk oil phase. The protonated polyaromatic molecules are found to preferentially adsorb at the oil-water interface in a head-on (or side-on) orientation with the aromatic core staying in the nonaqueous phase. The major findings from this work provide scientific insights in polyaromatic molecular associations in nonaqueous systems and in the design of proper chemical demulsifiers for polyaromatic mediated emulsions formed under specific process conditions of temperature, pressure and pH of heavy oil production.

[发布机构] University of Alberta

[效力级别] GROMOS96