New insights into bulk and interface properties of [Bmim][Ac]/[Bmim][BF4] ionic liquid/CO2 systems — Molecular dynamics simulation approach

Correlation-Based Predictions of Gas Solute Diffusivity in Ionic Liquid Solvents Based on Solvent-Accessible Surface Area

In our prior study [Olowookere, F. V.; Turner, C. H. J. Phys. Chem. B 2023, 127(42), 9144-9154], we introduced a new scaling relationship to predict gas solute diffusion at challenging conditions, focusing on CO2 and SO2 diffusion in multivalent ionic liquid (IL) solvents. This work extends our initial exploratory study into a much broader array of systems, encompassing additional solutes (N2, CH4, C2H6, C3H8, C3H8O, and H2O) and a variety of different ionic liquid species ([Bzmim3]3+, [Bzmim4]4+, [BMIM]+, [EMIM]+, [HMIM]+, [NapO2]2-, [BzO3]3-, [BF4]-, [Tf2N]-, and [PF6]-). Our study demonstrates a remarkably robust logarithmic correlation between solute diffusion and solvent accessible surface area (SA) across 20 different additional systems. We perform comprehensive analyses of the underlying molecular phenomena responsible for this correlation, including solute lifetime distributions, void space dynamics, and Voronoi tessellation, in order to elucidate a stronger mechanistic understanding of this behavior. Our findings highlight a direct link between the solvent accessible SA and the size of the void domains. Overall, our scaling approach provides an efficient and reliable approach for predicting diffusion from analyses of short simulations at higher temperatures.

Predicting Gaseous Solute Diffusion in Viscous Multivalent Ionic Liquid Solvents

Calculating solute diffusion in dense, viscous solvents can be particularly challenging in molecular dynamics simulations due to the long time scales involved. Here, a new scaling approach is developed for predicting solute diffusion based on analyses of CO2 and SO2 diffusion in two different multivalent ionic liquid solvents. Various scaling approaches are initially evaluated, including single and separate thermostats for the solute and solvent, as well as the application of the Arrhenius relationship and the Speedy-Angell power law. A very strong logarithmic correlation is established between the solvent-accessible surface area and solute diffusion. This relationship, reflecting Danckwerts' surface renewal theory and the Vrentas-Duda free volume model, presents a valuable method for estimating diffusion behavior from short simulation trajectories at elevated temperatures. The approach may be beneficial for enhancing predictive modeling in similar challenging systems and should be more broadly evaluated.

The effect of anion on aggregation of amino acid ionic liquid: Atomistic simulation

Aggregation behavior of dodecyl betaine chloride [DB][Cl], as an amino acid ionic liquid, and dodecyl betaine N-acetyl glycinate [DB][AG], as a bio ionic liquid, in aqueous media was studied through molecular dynamics simulation. The aggregating was investigated by radial distribution function, coordination numbers, and hydrogen bond numbers. The results demonstrated the hydrogen bond between [DB]⁺ and [AG]^- that leads to aggregation. The number of hydrogen bonds of [DB][AG] is greater than [DB][Cl] and causes a decrease in the gradient of the mean square displacement, thereby the diffusion coefficient of cation, anion, and water in [DB][AG]. The results point to a stable aggregation of [DB][AG] which is in agreement with the results of root mean square deviations. The aggregation number for [DB][AG] is 50 and 44 for [DB][Cl]. Computing the radius of gyration and geometrical radius shows that the aggregation size is 23.0 Å and 26.4 Å for [DB][AG] and [DB][Cl], respectively. It was also observed that the shape of the aggregates is quasi-spherical that points to a sub-diffusive regime.