Abstract
Ionic liquids have gained immense popularity in recent decades due to a combination of unique properties. Despite the widespread use of ionic liquids mixtures with aprotic dipolar solvents in electrochemistry, it remains relevant to predict their macroscopic, primarily transport, properties based on the microscopic picture of the entire set of interparticle interactions in such systems. The method of molecular dynamics simulation (MDS) is one of the most powerful tools for solving problems of this kind. However, one of the unsolved problems of the classical MDS of ion-molecular systems is the correct accounting of polarization effects. Recently it was proposed to use a variation of the effective ion charges in solutions to solve this task. This paper presents the results of the MDS structural and dynamic properties of 1-butyl-3-methylimidazolium (BmimBF4) and lithium (LiBF4) tetrafluoroborates solutions in propylene carbonate (PC) at 298.15 K in NPT ensemble using GROMACS and MDNAES software packages. The possibility of reproducing the experimental dynamic properties (diffusion coefficients of cations and solvent, viscosity, and electrical conductivity) of binary systems based on mixtures of ionic liquids with PC in a wide concentration range was shown. Polarization effects were taken into account by reducing the partial charges of the ion atoms. The structure of the solvation shell of cations was studied within the framework of radial distribution functions, distribution of coordination numbers and the presence of hydrogen bonds between the organic cation and solvent molecules. The results point to stronger and more structured solvation shell of the Li+ cation compared to Bmim+, which is consistent with the conclusions about the mobility of these cations. The reorientation times of propylene carbonate molecules and their lifetimes in the framework of the first solvation shells of the cations are several times higher for the lithium cation.
Highlights
В настоящей работе представлены результаты молекулярнодинамического моделирования (МДМ) структурных и динамических свойств растворов тетрафтороборатов 1-бутил-3-метилимидазолия (BmimBF4) и лития (LiBF4) в пропиленкарбонате (PC) при 298.15 К в NPT ансамбле с использованием программных пакетов GROMACS и MDNAES
Использование смесей ионных жидкостей (ИЖ) с молекулярными жидкостями также позволяет существенно снизить стоимость электролитной части электрохимических устройств [4,5]
The possibility of reproducing the experimental dynamic properties (diffusion coefficients of cations and solvent, viscosity, and electrical conductivity) of binary systems based on mixtures of ionic liquids with PC in a wide concentration range was shown
Summary
Параметры межмолекулярных взаимодействий для катионов и BF4- представлены в таблице 1. Колонки «заряд (±0.79)» и «заряд (±1)» указывают на различные использованные заряды для ионов (первые – из источника [23], вторые – пересчитанные нами согласно методике [28] с целью воспроизведения моделей потенциальных полей с целочисленными зарядами для сравнения). Моделирование проводили с использованием программного пакета GROMACS [26] и MDNAES [27]. Для всех этапов и систем использовался термостат V-rescale с временем релаксации 10 пс и баростат Берендсена с временем релаксации 1000 пс. Были проанализированы следующие системы: бесконечно разбавленные растворы катионов Bmim+, Li+ и аниона BF4 (1 молекула иона + 499 молекул PC), смеси пропиленкарбоната с ионной жидкостью различного мольного состава (таблица 2)
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