Formation of type III Deep Eutectic Solvents and effect of water on their intermolecular interactions Temirlan Zhekenov a , Nursultan Toksanbayev a , Zhanna Kazakbayeva a , Dhawal Shah a, * , Farouq S. Mjalli b a Department of Chemical Engineering, Nazarbayev University, Kazakhstan b Petroleum and Chemical Engineering Department, Sultan Qaboos University, Oman article info Article history: Received 30 October 2016 Received in revised form 9 January 2017 Accepted 22 January 2017 Available online xxx Keywords: Deep Eutectic Solvents Hydrogen bond Molecular interactions Molecular dynamics simulations Ionic liquids abstract Several novel applications of Deep Eutectic Solvents (DESs) have emerged recently. With a growing in- terest in the field, there is an urge to understand formation and functioning of these solvents at mo- lecular level, which in turn would assist in further designing of DESs. We herein performed molecular dynamics simulations on three of the commonly used type III DES, viz, reline, ethaline, and glyceline, which are mixtures of urea, ethylene glycol, and glycerol with choline chloride at eutectic composition. Our results explain the role of inter-molecular and intra-molecular hydrogen bonding and energies on formation of these DESs. Furthermore, the ability of these DESs to be altered in a desired way through a simple addition of water makes it versatile solution for several other applications. Hence, simulations are also performed on the aqueous DES solutions, which reveal the effect of water on intermolecular network of interaction existing within these DESs. © 2017 Elsevier B.V. All rights reserved. 1. Introduction Deep Eutectic Solvents (DESs) are considered as a new alterna- tive class of Ionic Liquids (ILs), which have attracted a great attention because of their favorable physical and thermodynamic properties [1]. Comparing to conventional ILs, DESs are relatively inexpensive and easy to prepare organic solvents [2,3]. DESs were first introduced by Abbott et al. [4] by combining a quaternary ammonium salt with hydrogen bond donor (HBD), thus forming a mixture, which had a melting point much lower than the individual components. This mixture is now categorized as type III eutectic solvents, where choline is mostly taken as quaternary ammonium cation and typical HBDs are urea, glycerol, ethylene glycol, malonic acid, and others. In comparison, type I is a combination of quater- nary ammonium salt with metal chloride (i.e. Zn, Sn, Fe, Al, Ga, and In), while mixture with hydrated metal halides, such as Cr, Co, Cu, Ni, Fe are type II DESs. Combination of metal chloride hydrates, generally with transition metals, and hydrogen bond donor is classified as type IV DESs [1,5]. In all of these cases, the product, DESs, is non-toxic, non-flammable, less volatile, and most importantly is an environmental friendly solvent [6]. DESs have been widely used in metal processing applications and synthesis/shape-control of metal nanoparticles [3]. In partic- ular, owing to higher metal solubility and conductivity in DESs, as compared to other commonly used solvent, DESs are also commercially used for electroplating [2]. Furthermore, DESs show great potential to be used for gas and liquid adsorption, for selective synthesis of organic compounds, and also for specifics biotrans- formation [2,4,7e11]. Adsorption and sequestering of carbon di- oxide are one of the main topics that is considered in reducing global warming and the importance of deep eutectic solvents in this sphere can be crucial because of its high efficiency and sus- tainability [3,12e14]. Apart from the above-mentioned usage, DESs have also been used for the enhancement of chemical and physical properties of some materials, maintaining their low cost. For example, Fang et al. [15], report an enhancement in thermal con- ductivity of graphene nanofluids synthesized in the DESs (in choline chloride e triethylene glycol & also in methyl triphenyl phosphonium bromide e ethylene glycol based DESs). Although several applications for DESs have been investigated, little, if any, interest has been placed in aqueous DESs solutions. Water in DESs can be regarded as an impurity, when being handled in commercial applications, or intentionally added to modulate the physicochemical properties of the solvent. For example, by * Corresponding author. E-mail address: dhawal.shah@nu.edu.kz (D. Shah). Contents lists available at ScienceDirect Fluid Phase Equilibria journal homepage: www.elsevier.com/locate/fluid http://dx.doi.org/10.1016/j.fluid.2017.01.022 0378-3812/© 2017 Elsevier B.V. All rights reserved. Fluid Phase Equilibria xxx (2017) 1e6 Please cite this article inpress as: T. Zhekenov, et al., Formation of type III Deep Eutectic Solvents and effect of water on their intermolecular interactions, Fluid Phase Equilibria (2017), http://dx.doi.org/10.1016/j.fluid.2017.01.022