Molecular dynamics simulation of electrolyte solutions confined by calcite mesopores

The tuning of the electrolyte content in water reinjected during the water flooding process has shown to contribute greatly to increase oil and gas recovery. This is directly related to the fact that different salts and conditions affect differently the electrical double layer formed on the mineral walls of the hydrocarbon reservoirs. Even though there has been a large number of experimental investigations on this topic, the understanding of the phenomena involved in water flooding at the molecular level still needs improvement. Here, we have used molecular dynamics simulations to describe at the atomistic level the formation of the electrical double layer close to the walls of a calcite mesopore. Aqueous electrolyte solutions that are representative of systems observed in the oil and gas industry are considered. Furthermore, the effect of confinement on the ionic conductivity is investigated. The insights obtained are expected to contribute to the specification of the properties of the water being reinjected during water flooding processes, aiming at a higher oil recovery depending on the characteristics of the reservoir

Quantifying pore width effects on diffusivity via a novel 3D stochastic approach with input from atomistic molecular dynamics simulations

The increased production of unconventional hydrocarbons emphasizes the need of understanding the transport of fluids through narrow pores. Although it is well known that confinement affects fluids structure and transport, it is not yet possible to quantitatively predict properties such as diffusivity as a function of pore width in the range of 1-50 nm. Such pores are commonly found in shale rocks, but also in a wide range of engineering materials, including catalysts. We propose here a novel and computationally efficient methodology to obtain accurate diffusion coefficient predictions as a function of pore width for pores carved out of common materials, such as silica, alumina, magnesium oxide, calcite and muscovite. We implement atomistic molecular dynamics (MD) simulations to quantify fluid structure and transport within 5 nm-wide pores, with particular focus on the diffusion coefficient within different pore regions. We then use these data as input to a bespoke stochastic kinetic Monte Carlo (KMC) model, developed to predict fluid transport in mesopores. The KMC model is used to extrapolate the fluid diffusivity for pores of increasing width. We validate the approach against atomistic MD simulation results obtained for wider pores. When applied to supercritical methane in slit-shaped pores, our methodology yields data within 10% of the atomistic simulation results, with significant savings in computational time. The proposed methodology, which combines the advantages of MD and KMC simulations, is used to generate a digital library for the diffusivity of gases as a function of pore chemistry and pore width and could be relevant for a number of applications, from the prediction of hydrocarbon transport in shale rocks to the optimization of catalysts, when surface-fluid interactions impact transport

Effect of surface chemistry on the electrical double layer in a long-chain ionic liquid

International audienceRoom temperature ionic liquids (ILs) can create a strong accumulation of charges at solid interfaces by forming a very thin and dense electrical double layer (EDL). The structure of this EDL has important consequences in numerous applications involving ILs, for example in supercapacitors, sensors and lubricants, by impacting the interfacial capacitance, the charge carrier density of semiconductors , as well as the frictional properties of the interfaces. We have studied the interfacial structure of a long chain imidazolium-based IL (1-octyl-3-methylimidazolium dicyanamide) on several substrates: mica, silica, silicon and molybdenum disulfide (MoS 2), using atomic force microscopy (AFM) experiments and molecular dynamics (MD) simulations. We have observed 3 types of interfacial structures for the same IL, depending on the chemistry of the substrate and the water content, showing that the EDL structure is not an intrinsic property of the IL. We evidenced that at a low water content, neutral and apolar (thus hydrophobic) substrates promote a thin layer structure, where the ions are oriented parallel to the substrate and cations and anions are mixed in each layer. In contrast, a strongly charged (thus hydrophilic) substrate yield an extended structuration into several bilayers, while a heterogeneous layering with loose bilayer regions was observed on an intermediate polar and weakly charged substrate and on an apolar one at a high bulk water content. In the latter case, water contamination favors the formation of bilayer patches by promoting the segregation of the long chain IL into polar and apolar domains

A modified Poisson-Boltzmann equation applied to protein adsorption

Ion-exchange chromatography has been widely used as a standard process in purification and analysis of protein, based on the electrostatic interaction between the protein and the stationary phase. Through the years, several approaches are used to improve the thermodynamic description of colloidal particle surface interaction systems, however there are still a lot of gaps specifically when describing the behavior of protein adsorption. Here, we present an improved methodology for predicting the adsorption equilibrium constant by solving the modified Poisson-Boltzmann (PB) equation in bispherical coordinates. By including dispersion interactions between ions and protein, and between ions and surface, the modified PB equation used can describe the Hofmeister effects. We solve the modified Poisson-Boltzmann equation to calculate the protein-surface potential of mean force, treated as spherical colloid-plate system, as a function of process variables. From the potential of mean force, the Henry constants of adsorption, for different proteins and surfaces, are calculated as a function of pH, salt concentration, salt type, and temperature. The obtained Henry constants are compared with experimental data for several isotherms showing excellent agreement. We have also performed a sensitivity analysis to verify the behavior of different kind of salts and the Hofmeister effects

Thermotropic Ionic Liquid Crystals: Structure/ion transport correlation within stimuli-responsive electrolytes for energy

International audienceThermotropic Ionic Liquid Crystals (TILCs) have recently emerged as a smart class of organic electrolytes encoding the unique hierarchical self-assembling properties and stimuli-responsive mosaicity of mesophases featured by thermotropic liquid crystals with the efficient ion transport of ionic liquids. As a result, TILCs stand out as a promising electrolytic platform for energy storage (batteries/supercapacitors) and conversion (fuel cells/DSSCs) as they use industry-compatible and simple-to-implement manufacturing processes. The multi-scale correlation relating their structures and (an/cat)ionic transport properties is crucial to pave understanding of their ionic transport. A fundamental question of interest is here the influence of the dynamical mosaicity related to the average size of their self-assembled domains, with or without (w vs. w/o) dynamic grain boundaries. Remarkably, stimuli such as electric or magnetic field can be leveraged to sample (dis)order till ultimately reaching monodomains (eradication of mosaicity) to reveal inherent (i.e. defect-free) features of their ionic transport.Exploring this research endeavour, in this communication, the case study of an anionic conductive TILC (A-TILC) composed of an imidazolium-based cation with symmetrical n-alkyl chains (C18C18Im+) and a N(CN)2- anion featuring a Smectic A (SmA) mesophase (lamellar organization) will be deciphered by combining state-of-the-art (SoA) theoretical and experimental approaches. First, coarse-grained simulations derived from Martinelli will be presented to unravel its set of structural and dynamic descriptive parameters. Second, an unique operando experiment combining (synchrotron-based) SoA structural studies (SAXS+WAXS) with ionic transport measurements (probed by EIS) w vs. w/o a tuneable (0 up to 1T) magnetic field (Fig. 1) will be introduced, allowing in-depth study of the interplay linking its structure with its ion transport properties. In closing and beyond the case study of an A-TILC encoding a nanoconfined 2D transport within a SmA mesophase, we will illustrate the potential offered by TILCs to impart next generation (conversion/storage) energy devices with self-healing functionalities

Thermotropic Ionic Liquid Crystals: Structure/ion transport correlation within stimuli-responsive electrolytes for energy

International audienceThermotropic Ionic Liquid Crystals (TILCs) have recently emerged as a smart class of organic electrolytes encoding the unique hierarchical self-assembling properties and stimuli-responsive mosaicity of mesophases featured by thermotropic liquid crystals with the efficient ion transport of ionic liquids. As a result, TILCs stand out as a promising electrolytic platform for energy storage (batteries/supercapacitors) and conversion (fuel cells/DSSCs) as they use industry-compatible and simple-to-implement manufacturing processes. The multi-scale correlation relating their structures and (an/cat)ionic transport properties is crucial to pave understanding of their ionic transport. A fundamental question of interest is here the influence of the dynamical mosaicity related to the average size of their self-assembled domains, with or without (w vs. w/o) dynamic grain boundaries. Remarkably, stimuli such as electric or magnetic field can be leveraged to sample (dis)order till ultimately reaching monodomains (eradication of mosaicity) to reveal inherent (i.e. defect-free) features of their ionic transport.Exploring this research endeavour, in this communication, the case study of an anionic conductive TILC (A-TILC) composed of an imidazolium-based cation with symmetrical n-alkyl chains (C18C18Im+) and a N(CN)2- anion featuring a Smectic A (SmA) mesophase (lamellar organization) will be deciphered by combining state-of-the-art (SoA) theoretical and experimental approaches. First, coarse-grained simulations derived from Martinelli will be presented to unravel its set of structural and dynamic descriptive parameters. Second, an unique operando experiment combining (synchrotron-based) SoA structural studies (SAXS+WAXS) with ionic transport measurements (probed by EIS) w vs. w/o a tuneable (0 up to 1T) magnetic field (Fig. 1) will be introduced, allowing in-depth study of the interplay linking its structure with its ion transport properties. In closing and beyond the case study of an A-TILC encoding a nanoconfined 2D transport within a SmA mesophase, we will illustrate the potential offered by TILCs to impart next generation (conversion/storage) energy devices with self-healing functionalities

Thermotropic Ionic Liquid Crystals: Structure/ion transport correlation within stimuli-responsive electrolytes for energy

International audienceThermotropic Ionic Liquid Crystals (TILCs) have recently emerged as a smart class of organic electrolytes encoding the unique hierarchical self-assembling properties and stimuli-responsive mosaicity of mesophases featured by thermotropic liquid crystals with the efficient ion transport of ionic liquids. As a result, TILCs stand out as a promising electrolytic platform for energy storage (batteries/supercapacitors) and conversion (fuel cells/DSSCs) as they use industry-compatible and simple-to-implement manufacturing processes. The multi-scale correlation relating their structures and (an/cat)ionic transport properties is crucial to pave understanding of their ionic transport. A fundamental question of interest is here the influence of the dynamical mosaicity related to the average size of their self-assembled domains, with or without (w vs. w/o) dynamic grain boundaries. Remarkably, stimuli such as electric or magnetic field can be leveraged to sample (dis)order till ultimately reaching monodomains (eradication of mosaicity) to reveal inherent (i.e. defect-free) features of their ionic transport.Exploring this research endeavour, in this communication, the case study of an anionic conductive TILC (A-TILC) composed of an imidazolium-based cation with symmetrical n-alkyl chains (C18C18Im+) and a N(CN)2- anion featuring a Smectic A (SmA) mesophase (lamellar organization) will be deciphered by combining state-of-the-art (SoA) theoretical and experimental approaches. First, coarse-grained simulations derived from Martinelli will be presented to unravel its set of structural and dynamic descriptive parameters. Second, an unique operando experiment combining (synchrotron-based) SoA structural studies (SAXS+WAXS) with ionic transport measurements (probed by EIS) w vs. w/o a tuneable (0 up to 1T) magnetic field (Fig. 1) will be introduced, allowing in-depth study of the interplay linking its structure with its ion transport properties. In closing and beyond the case study of an A-TILC encoding a nanoconfined 2D transport within a SmA mesophase, we will illustrate the potential offered by TILCs to impart next generation (conversion/storage) energy devices with self-healing functionalities