Comparison of two protic ionic liquid behaviors in the presence of an electric field using molecular dynamics

Mehta, Neil A.; Levin, Deborah A.

doi:10.1063/1.5001827

Cited by 14 publications

(8 citation statements)

References 40 publications

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“…Addition of hydroxyl groups to terminal methyl groups in EA cations leads to a disruption of solvophobic associations between alkyl chains in EtAN, resulting in small ion aggregates, rather than a spongelike liquid morphology with extended networks. , EtAN has a less ordered liquid arrangement than that of EAN since [NO 3 ] anions are competitively coordinated with both ammonium and hydroxyl groups in EtA cations via strong HB interactions. , Generally, inclusion of additional HBs represents a source of defects in polar networks, leading to more disordered microstructures in ILs. ,,, In addition, both translational and rotational dynamics of constituent ions slow down due to the formation of HB networks in IL matrixes. When an external electric field is applied, EtAN requires a lower electric field strength than that for EAN to emit ion pairs . The applied electric field can effectively reduce the number of hydroxyl–[NO 3 ] HBs but is less effective in disrupting HBs between N–H head groups and [NO 3 ] anions.…”

Section: Pure Ionic Liquidsmentioning

confidence: 99%

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Microstructural and Dynamical Heterogeneities in Ionic Liquids

et al. 2020

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Ionic liquids (ILs) are a special category of molten salts solely composed of ions with varied molecular symmetry and charge delocalization. The versatility in combining varied cation−anion moieties and in functionalizing ions with different atoms and molecular groups contributes to their peculiar interactions ranging from weak isotropic associations to strong, specific, and anisotropic forces. A delicate interplay among intra-and intermolecular interactions facilitates the formation of heterogeneous microstructures and liquid morphologies, which further contributes to their striking dynamical properties. Microstructural and dynamical heterogeneities of ILs lead to their multifaceted properties described by an inherent designer feature, which makes ILs important candidates for novel solvents, electrolytes, and functional materials in academia and industrial applications. Due to a massive number of combinations of ion pairs with ion species having distinct molecular structures and IL mixtures containing varied molecular solvents, a comprehensive understanding of their hierarchical structural and dynamical quantities is of great significance for a rational selection of ILs with appropriate properties and thereafter advancing their macroscopic functionalities in applications. In this review, we comprehensively trace recent advances in understanding delicate interplay of strong and weak interactions that underpin their complex phase behaviors with a particular emphasis on understanding heterogeneous microstructures and dynamics of ILs in bulk liquids, in mixtures with cosolvents, and in interfacial regions.

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Section: Pure Ionic Liquidsmentioning

confidence: 99%

“…When an external electric field is applied, EtAN requires a lower electric field strength than that for EAN to emit ion pairs. 331 The applied electric field can effectively reduce the number of hydroxyl−[NO 3 ] HBs but is less effective in disrupting HBs between N−H head groups and [NO 3 ] anions.…”

Section: Free Ions Ion Pairs and Ion Clustersmentioning

confidence: 99%

Microstructural and Dynamical Heterogeneities in Ionic Liquids

et al. 2020

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“…The average number of anions surrounding a cation, also known as the coordination number of EAN, was observed to be 1.9, and that of EMIM-BF 4 was 1.5, suggesting that the bulk structure of EAN is more closely packed than of EMIM-BF 4 . In other previous work [35], it was observed that EAN contains an extensive network of hydrogen bonds, which is not present in EMIM-BF 4 , possibly making the emission of ion-pairs from the EAN bulk more difficult to achieve than EMIM-BF 4 for the same extraction voltage.…”

Section: Comparison Of the Cation-anion Separation Energy Of Ean Vs mentioning

confidence: 85%

“…This explains the fundamental differences that exist in the emission characteristics of EAN and EMIM-BF 4 ILs. The extensive network of hydrogen bonds existing in EAN provides resistance to the separation of cations and anions [35]. However, it should be noted that only the normal electric field was used in these bulk simulations to separate the cation-anion pair, and the presence of both the normal and radial fields will make the emission of ions easier.…”

Section: Comparison Of the Cation-anion Separation Energy Of Ean Vs mentioning

confidence: 99%

Molecular Dynamics Electrospray Simulations of Coarse-Grained Ethylammonium Nitrate (EAN) and 1-Ethyl-3-Methylimidazolium Tetrafluoroborate (EMIM-BF4)

Mehta

Levin

2017

Aerospace

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In this work, the use of molecular dynamics as a predictive tool for modeling the atomistic behavior of electrospray propulsion is discussed. 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM-BF 4 ) and ethylammonium nitrate (EAN) were considered as two limits of ionic liquid (IL) propellants that tend to operate in an ion versus a droplet mode. The emission modes were found to depend on the electro-chemical properties of the IL propellant. The aprotic EMIM-BF 4 -based electrospray emitted primarily monomers and trimers as the dominant species and only small quantities of droplets. In contrast, trimers were the dominant emitted species in the protic EAN emissions with a significantly large contribution from droplets towards the total emission current, suggesting that EMIM-BF 4 -based colloid thrusters operate in ion mode and EAN-based devices operate in the droplet mode. Furthermore, the formation of the Taylor cone was found to depend on the mass flow rate and the external electric field strength. This paper provides a framework that can be extended for use to simulate any other ILs or their combinations.Aerospace 2018, 5, 1 2 of 18 mode [10]. On the other hand, ethylammonium nitrate (EAN) is classified as a protic IL, which are known to be environmentally more benign than other organic solvents [11] and easier to synthesize compared to aprotic ILs [12]. EAN has been reported to emit in the droplet mode, producing a jet of nanodroplets [13]. The electro-chemical properties of the ILs used as propellants and their mass flow rates determine the mode of operation of the colloid thruster. Extensive research has been performed to determine the emission modes of the colloid thrusters. Since future propellants may use mixtures of protic and aprotic types of ILs, molecular dynamics (MD) electrospray simulations can be used to analyze the differences in the emission behavior specific to these two types of ILs.A large number of ILs can be used as propellants for electrosprays [14,15], and the availability of a large number of inter-atomic potentials also makes it possible to model virtually any of the ILs. However, MD simulations scale on the order of O(N 2 ), where, N is the number of atoms, making MD very expensive to model large simulations (>10,000 atoms) typically used to study electrosprays. In this work, effective field coarse graining method [16,17] was used to derive coarse-grained potential of EAN, and its efficacy for the electrospray processes was verified by successfully performing MD simulations of Taylor cone formation and subsequent emission of ion-species. Previous works [16][17][18] have derived coarse-grained (CG) potentials to verify bulk IL physical properties or have used approximations to modify the CG potential to perform electrospray simulations [19,20].Prior to designing colloid thrusters, it is necessary to have a simulation-based ability to predict thrust, required voltages and the mode of operation. MD is a particle-based method that allows one to understand the nature of electrosprays at ...

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“…1. The electrochemical properties of EAN have been analyzed in detail using both, experiments [33] and MD simulations [31,34,35]. Lenguito, et al [36] and Alonso-Matilla, et al [37] have experimentally shown that…”

Section: Figmentioning

confidence: 99%

Electrospray molecular dynamics simulations using an octree-based Coulomb interaction method

Mehta

Levin

2019

Phys. Rev. E

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A new octree-based Coulomb interaction model is developed to model the electrospray of ionic liquids (ILs) in molecular dynamics (MD). Using an octree-based method, Coulomb interactions are categorized as intra-and inter-leaf Coulomb interactions based on a criterion related to the Bjerrum length of the IL. The octree-based method is found capable of reproducing Coulomb energy in agreement with established and computationally more expensive models, such as the direct Coulomb and the Damped Shifted Force (DSF) method in the absence of an external electric field. In the presence of an external electric field, the octree-based method produces distinctly different results compared to that obtained by the direct Coulomb method. The time required to form Taylor's cone was shorter for the octree method compared to the direct Coulomb approach. While no emission larger than monomers was observed from the direct Coulomb simulation, emission of larger species such as dimers and trimers was observed when the octree-based Coulomb interaction model was used. Furthermore, the octree-based model forms a smaller ion emission cone compared to that from the direct Coulomb method.

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Comparison of two protic ionic liquid behaviors in the presence of an electric field using molecular dynamics

Cited by 14 publications

References 40 publications

Microstructural and Dynamical Heterogeneities in Ionic Liquids

Microstructural and Dynamical Heterogeneities in Ionic Liquids

Molecular Dynamics Electrospray Simulations of Coarse-Grained Ethylammonium Nitrate (EAN) and 1-Ethyl-3-Methylimidazolium Tetrafluoroborate (EMIM-BF4)

Electrospray molecular dynamics simulations using an octree-based Coulomb interaction method

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