The diffusion coefficient of Li+ ions decreases with increase in LiCl concentration which depends on the size of coordination structure of ions formed in solutions.

Asphaltenes are the heaviest component of crude oil, causing the formation of a stable oil−water emulsion. Even though asphaltenes are known to behave as an emulsifying agent for emulsion formation, their arrangement at the oil−water interface is poorly understood. We investigated the effect of asphaltene structure (island type vs archipelago type) and heteroatom type (Oxygen-O, Nitrogen-N, and Sulfur-S) on their structural behavior in the oil−water system. Out of six asphaltenes studied here, only three asphaltenes remain at the oil−water interface while others are soluble in the oil phase. Molecular orientation of asphaltene at the interface, position, and angle of asphaltene with the interface has also been determined. We observed that the N-based island type asphaltene is parallel, while the O-based island type asphaltene and Nbased archipelago type are perpendicular to the interface. These asphaltene molecules are anchored at the interface by the heteroatom. The S-based asphaltenes (both island and archipelago type) and O-based archipelago type asphaltenes are soluble in the oil phase due to their inability to form a hydrogen bond with water and steric crowding near the heteroatom. This study will help in understanding the role of asphaltenes in oil−water emulsion formation based on its structure and how to avoid it.

The deposition of high asphaltene-containing crude oil on mineral surfaces and pipelines is a technical as well as an economic problem in the oil industry. In enhanced oil recovery techniques, additives and emulsifiers are used to detach oil from the mineral surface. It requires detailed knowledge of the type of interaction taking place at the molecular level between the rock surface and the crude oil to target the most dominant interacting part for site-specific design of emulsifiers. In this work, we have studied energetics of saturate and asphaltene molecules of crude oil with mica mineral surfaces in the presence of dodecane solvent using molecular dynamics simulations. Five different types of asphaltene molecules (three island type and two archipelago type) containing one heteroatom (oxygen, nitrogen, and sulfur) were considered in this study. We have calculated the potential of mean force using an umbrella sampling technique. The adsorption free energy of saturate molecules is significantly lower compared to asphaltene molecules because of the presence of the heteroatom. Asphaltene molecules with a polar heteroatom (oxygen and nitrogen) interact with mica surface strongly as compared to asphaltene molecules with a nonpolar heteroatom (sulfur). The structural behavior of asphaltene molecules at the mica–oil interface is governed by the balance of enthalpic interactions between aromatic core atoms and the steric hindrance of aliphatic chain atoms with the mica surface. Asphaltene molecules with smaller aliphatic chains are arranged parallel to the mica surface. In contrast, those molecules which have more and bigger aliphatic chains were found to have their aromatic core tilted to the mica surface. This detailed information would be useful for designing better additives to displace heavy and residual oil from the rock surface.

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Preorganized ligands with imidazolium arms have been found to be highly selective in extracting Am­(III) into ionic liquids (ILs), but the detailed structure and mechanism of the complexation process in the ionic solvation environment are unclear. Here, we carry out molecular dynamics simulation of the complexation of Am­(III) with a preorganized 1,10-phenanthroline-2,9-dicarboxamide complexant (L) functionalized with alkyl chains and imidazolium cations in the butylmethylimidazolium bistriflimide ([BMIM]­[NTf2]) IL. Both Am:L (1:1) and Am:L2 (1:2) complexes are examined. In the absence of the ligand, Am­(III) is found to be coordinated by six NTf2 anions via nine O donors in the first solvation shell. In the Am:L complex, Am­(III) is coordinated to the ligand via two O donors and four NTf2 anions via seven O donors in the first coordination shell. In the Am:L2 complex, Am­(III) is coordinated to the two ligands via four O donors and four NTf2 anions via five O donors. The imidazolium arms of the ligands play an important role in the secondary solvation environment by attracting NTf2 anions closer to the metal center. As a result, we find that the binding free energy for the second L2+ ligand is twice that for the first L2+ ligand, making the Am:L2 complex significantly more stable than the Am:L complex. This work highlights the multiple factors and tunability in using preorganized ligands with charged functional groups in an ionic solvation environment, which could hold the key to achieving desired selectivity in ion extraction efficiency.

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