Understanding Adsorption of Violanthrone-79 as a Model Asphaltene Compound on Quartz Surface Using Molecular Dynamics Simulations

A series of molecular dynamics simulations were performed to investigate the adsorption of violanthrone-79 (VO-79) as a model asphaltene compound on quartz surface in different organic solvents (n-heptane, toluene, and heptol with three different n-heptane/toluene volume ratios). Our simulations demonstrated that the type of solvent had a great impact on the kinetics of adsorption, such as the adsorption rate and final adsorption amount. However, the equilibrium modes of adsorption were similar: both monomer heptane and toluene contents. With monomer adsorption, the and aggregate adsorptions were observed regardless of the n-polyaromatic core (PAC) of VO-79 was merely parallel to the surface, whereas the PACs showed two types of orientations in aggregate adsorption-parallel and slant-with the majority of them slant to the surface, maintaining pi-pi stacking between neighboring PACs. Energetic analyses showed that the adsorption was driven primarily by van der Waals forces, accompanied by electrostatic interactions, hydrogen bonding, and free energy of solvation. The results reported here provide valuable insights at the molecular level into the mechanistic understanding of asphaltene adsorption on mineral surfaces in organic media.