Bulk and interfacial structures of reline deep eutectic solvent: A molecular dynamics study

Insights on (C, BN, Si, Ge, MoS2) Nanotubes in Reline Deep Eutectic Solvent

The properties of carbon, boron nitride, silicon, germanium, and molybdenum disulfide nanotubes in reline (cholinium chloride + urea) deep eutectic solvents were studied by using classical molecular dynamics simulations. These nanotubes + reline nanofluids provide a suitable platform for the development of sustainable thermal engineering applications. The reported results lead to the characterization of nanotube solvation and reline layering around the nanotube surfaces as well as the behavior of reline upon confinement inside the considered nanotube cavities. Changes in reline hydrogen bonding in the presence of the nanotubes are also analyzed and related with the development of stable nanotube dispersions, thus showing reline as a suitable vehicle for nanotubes.

Deep Eutectic Solvent Reline at 2D Nanomaterial Interfaces

The behavior of reline (choline chloride mixed with urea at a 1-to-2 mole ratio) deep eutectic solvent at the interfaces of 2D nanomaterials was studied by using molecular simulation methods. Graphene, boron nitride, silicene, germanene, and molybdenum disulfide were studied for considering the most relevant features of available 2D nanomaterials. The reline-nanomaterial interactions were analyzed, and the mechanism of reline adsorption with the properties at the interfaces was studied. Likewise, the behavior of the deep eutectic solvent upon confinement between parallel nanosheets was considered as a model of properties when placed in slit nanopores. The results provide a nanoscopic vision of the adsorption and confinement of reline regarding 2D nanomaterials, thus advancing the development of new materials based on deep eutectics.

Insight into Speciation and Electrochemistry of Uranyl Ions in Deep Eutectic Solvents

Understanding the speciation of metal ions in heterogeneous hydrogen-bonded deep eutectic solvents (DES) has immense importance for their wide range of applications in green technology, environmental remediation, and nuclear industry. Unfortunately, the fundamental nature of the interaction between DES and actinide ions is almost completely unknown. In the present work, we outline the speciation, solvation mechanism, and redox chemistry of uranyl ion (UO₂²⁺) in DES consisting of choline chloride (ChCl) and urea as the hydrogen-bond donor. Electrochemical and spectroscopic techniques along with molecular dynamics (MD) simulations have provided a microscopic insight into the solvation and speciation of the UO₂²⁺ ion in DES and also on associated changes in physical composition of the DES. The hydrogen-bonded structure of DES plays an important role in the redox behavior of the UO₂²⁺ ion because of its strong complexation with DES components. X-ray absorption spectroscopy and MD simulations showed strong covalent interactions of uranyl ions with the constituents of DES, which led to rearrangement of the hydrogen-bonding network in it without formation of any clusters or aggregations. This, in turn, stabilizes the most unstable pentavalent uranium (UO₂⁺) in the DES. MD analysis also highlights the fact that the number of H-bonds is reduced in the presence of uranyl nitrate irrespective of the presence of water with respect to pristine reline, which suggests high stability of the formed complexed species. The effect of added water up to 20 v/v % on speciation is insignificant for DES, but the presence of water influences the redox chemistry of UO₂²⁺ ions considerably. The fundamental findings of the present work would have far reaching consequences on understanding DES, particularly for application in the field of nuclear fuel reprocessing.

Heterogeneity in the microstructure and dynamics of tetraalkylammonium hydroxide ionic liquids: insight from classical molecular dynamics simulations and Voronoi tessellation analysis

Microscopic structural and dynamic heterogeneities were investigated for three ionic liquids (ILs), tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide employing classical molecular dynamics (MD) simulations.

Dielectric relaxation of deep eutectic solvent + water mixtures: structural implications and application to microwave heating

All dipolar species at their full individual strengths but synchronized in motion: structural implications of cooperative dynamics in glyceline/water and reline/water mixtures.

Nanostructure of the deep eutectic solvent/platinum electrode interface as a function of potential and water content

The interfacial nanostructure of the three most widely-studied Deep Eutectic Solvents (DESs), choline chloride:urea (ChCl:Urea), choline chloride:ethylene glycol (ChCl:EG), and choline chloride:glycerol (ChCl:Gly) at a Pt(111) electrode has been studied as a function of applied potential and water content up to 50 wt%. Contact mode atomic force microscope (AFM) force-distance curves reveal that for all three DESs, addition of water increases the interfacial nanostructure up to ∼40 wt%, after which it decreases. This differs starkly from ionic liquids, where addition of small amounts of water rapidly decreases the interfacial nanostructure. For the pure DESs, only one interfacial layer is measured at OCP at 0.5 nm, which increases to 3 to 6 layers extending ∼5 nm from the surface at 40 or 50 wt% water. Application of a potential of ±0.25 V to the Pt electrode for the pure DESs increases the number of near surface layers to 3. However, when water is present the applied potential attenuates the steps in the force curve, which are replaced by a short-range exponential decay. This change was most pronounced for ChCl:EG with 30 wt% or 50 wt% water, so this system was probed using cyclic voltammetry, which confirms the interfacial nanostructure is akin to a salt solution.

What a difference a methyl group makes - probing choline-urea molecular interactions through urea structure modification

There is a lack of fundamental knowledge on deep eutectic solvents, even for the most extensively studied mixtures, such as the mixture of cholinium chloride and urea, which prevents a judicious choice of components to prepare new solvents. The objective of this work is to study and understand the fundamental interactions between cholinium chloride and urea that lead to the experimentally observed melting temperature depression. To do so, the structure of urea was strategically and progressively modified, in order to block certain interaction centres, and the solid-liquid equilibrium data of each new binary system was experimentally measured. Using this approach, it was concluded that the most important interaction between cholinium chloride and urea occurs through hydrogen bonding between the chloride anion and the amine groups. Any blockage of these groups severely hampers the melting point depression effect. Raman spectroscopy and DFT calculations were utilized to study in more detail this hydrogen bonding and its nuances.

Influence of Hydration on the Structure of Reline Deep Eutectic Solvent: A Molecular Dynamics Study

In this article, we have performed an all-atom molecular dynamics simulation study to investigate the influence of water on the molecular level arrangement of reline deep eutectic solvent for different hydration levels ranging from 3.4 to 58.1 wt % of water and complemented the observations of recently measured neutron scattering experimental data. This study is particularly important because water is being introduced as a second hydrogen bond donor/acceptor in reline, wherein the structure is primarily governed by hydrogen bonding and electrostatic interactions. We have analyzed the simulated X-ray scattering structure functions, their partial components, and hydrogen bonding interactions to understand the effects of water on various intermolecular interactions in reline-water mixtures. It is observed that at lower hydration level, reline structure is qualitatively retained. At higher hydration level, most water molecules preferentially solvate chloride anions and ammonium group of choline cations mostly impacting choline-choline, choline-chloride, and chloride-chloride interactions. The present study reveals that at and above 41 wt % of water, the molecular arrangement of reline drastically changes and set to transition from reline to an aqueous solution of reline components with further increase in the hydration level. Hydrogen bond analysis reveals the presence of strong chloride-water H-bonding interaction, which gradually replaces choline-chloride and urea-chloride hydrogen bondings as the hydration level in the mixture increases.

Atomistic Insight into the Electrochemical Double Layer of Choline Chloride-Urea Deep Eutectic Solvents: Clustered Interfacial Structuring

Green, stable, and wide electrochemical window deep eutectic solvents (DESs) are ideal candidates for electrochemical systems. However, despite several studies of their bulk properties, their structure and properties under electrified confinement have barely been investigated, which has hindered widespread use of these solvents in electrochemical applications. In this Letter, we explore the electrical double layer structure of 1:2 choline chloride-urea (Reline), with a particular focus on the electrosorption of the hydrogen bond donor on a graphene electrode using atomistic molecular dynamics simulations. We discovered that the interface is composed of a mixed layer of urea and counterions followed by a mixed charged clustered structure of all of the Reline components. This interfacial structuring is strongly dependent on the balance between intermolecular interactions and surface polarization. These results provide new insights into the electrical double layer structure of a new generation of electrolytes whose interfacial structure can be tuned at the molecular level.