Ionic Pairing and Selective Solvation of Butylmethylimidazolium Chloride Ion Pairs in DMSO–Water Mixtures: A Comprehensive Examination via Molecular Dynamics Simulations and Potentials of Mean Force Analysis

Abstract

Ionic liquids (ILs) with dimethyl sulfoxide (DMSO) and water act as a promising solvent medium for the dissolution of cellulose in an efficient manner. To develop a proper solvent system, it is really important to understand the thermodynamics of the molecular solutions consisting of ILs, DMSO, and water. The ion-pairing propensity of the ILs in the presence of DMSO and water plays a crucial role in governing the property of the solvent mixtures. Employing all-atom molecular dynamics simulations, we estimate the potentials of mean force between BMIM + and Cl − ions in DMSO−water mixtures. Analysis reveals a significant increase in the thermodynamic stability of both contact ion pair (CIP) and solvent-assisted ion pair (SAIP) states with a rising DMSO mole fraction. Thermodynamic assessments highlight the entropic stabilization of CIP states and SAIP states in pure water, in DMSO−water mixtures, and in pure DMSO. The structural analysis reveals that in comparison to the DMSO local density, the local water density is relatively very high around ion pairs, more specifically in the solvation shell of a chloride ion. Preferential binding coefficients also consistently indicate exclusion of DMSO from the ion pair in DMSO−water mixtures. To enhance our understanding regarding the solvent molecules kinetics around the ion pairs, the survival probabilities of DMSO and water are computed. The calculations reveal that the water molecules prefer a prolonged stay in the solvation shell of Cl − ions.

Exploring the Role of Hydroxy- and Phosphate-Terminated cis-1,4-Polyisoprene Chains in the Formation of Physical Junction Points in Natural Rubber: Insights from Molecular Dynamics Simulations

“…The observation indicates that the end-groups encounter each other with a certain fraction; however, their stability as branch points or stable clusters remains undetermined. To address this, potentials of mean force (PMFs) have emerged as a widely used approach for assessing the stability of clusters in various research studies. ,,− In this study, we compute the PMFs between the terminal groups using the following equation W ( r ) = prefix− k B T .25em log ( g false( r false) ) where T is the temperature of the system, k B is the Boltzmann constant in kJ mol –1 /K, and g ( r ) represents the radial distribution function between the terminal groups. This equation allows us to derive the PMFs, which provide essential insights into the thermodynamic stability and interactions of the terminal groups in the system.…”