Relaxation of Voronoi shells in hydrated molecular ionic liquids

Abstract

The relaxation of solvation shells is studied following a twofold strategy based on a direct analysis of simulated data as well as on a solution of a Markovian master equation. In both cases solvation shells are constructed by Voronoi decomposition or equivalent Delaunay tessellation. The theoretical framework is applied to two types of hydrated molecular ionic liquids, 1-butyl-3-methyl-imidazolium tetrafluoroborate and 1-ethyl-3-methyl-imidazolium trifluoromethylsulfonate, both mixed with water. Molecular dynamics simulations of both systems were performed at various mole fractions of water. A linear relationship between the mean residence time and the system's viscosity is found from the direct analysis independent of the system's type. The complex time behavior of shell relaxation can be modeled by a Kohlrausch-Williams-Watts function with an almost universal stretching parameter of 1/2 indicative of a square root time law. The probabilistic model enables an intuitive interpretation of essential motional parameters otherwise not accessible by direct analysis. Even more, incorporating the square root time law into the probabilistic model enables a quantitative prediction of shell relaxation from very short simulation studies. In particular, the viscosity of the respective systems can be predicted.

Computational analysis of the solvation of coffee ingredients in aqueous ionic liquid mixtures

“…Consequently, we applied a different approach, the so-called Voronoi tessellation, 67,68 which is parameter free. Here, the complete space is decomposed into irregular polyhedra.…”

Domain Analysis in Nanostructured Liquids: A Post‐Molecular Dynamics Study at the Example of Ionic Liquids

“…It is as imple, direct, and automated analysis that does not need evaluation of the structureb eforehand in terms of, for example, first solvents hell minima. [32][33][34][35] Recently, we suggested to use radical Voronoi tessellation to decompose electronic density.T he obtainedd ipole moments were used to calculate the IR spectra of ionic liquids. Althought he fluorouss ide chains are also more or lessc onnected in one or, maximally,two domains, the alkyl phases are dispersed.…”

On the collective network of ionic liquid/water mixtures. IV. Kinetic and rotational depolarization

“…We reported in Ref. 57 mean residence times of cation-anion contacts of 64.0, 147.7, and 454.8 ps for c IL = 1.25, 2.52, and 3.77 M, respectively. If charged or neutral clusters of ions move in one direction for this period of time, the rotation of neighboring water dipoles cannot be correlated with the electric current since cations and anions moving in the same direction prefer different water orientations.…”

“…17 The volume fractions of water, W , and of the ionic liquid, IL , were computed by Voronoi decomposition. 17,57 In a second step, the water volume fraction W is further decomposed into bulk, bulk , and hydration water, hyd , based on a three exponential fit (k = 1. . .…”