Molecular dynamics study on TOTO-based ionic liquids with different cations

Abstract

Ionic liquids (ILs) have good designability and promising prospect of application. By changing different cations or anions, ILs possessing better and specific properties can be synthesized. In this paper, molecular dynamics (MD) simulation is applied to study ILs with the anion of 2,5,8,11-tetraoxatridecan-13-oate (TOTO), which are named as TOTO-based ILs. Attention is mainly paid to the effect of five different types of cations, including organic choline (Ch), tetraethylammonium (TEA), tetrapropylammonium(TPA), and tetrabutylammonium (TBA) and inorganic sodium (Na) ions, on the structure and properties of TOTO-based ILs. Results about conformation and length distribution of TOTO chain, distance between cations and TOTO anions, distribution of coordination number for cation-anion, and dynamic coordination are analysed, showing that changing cations makes no considerable influence on gauche probability along TOTO chain. All organic cation-TOTO ILs have similar TOTO chain length distribution, and similar radical function distributions between cations and anions. No matter inorganic cations and organic cations, these cations prefer to interact with carboxyl oxygen atoms. For organic cation-TOTO systems, interionic coordination interactions are weakened with the increase of cation size. Due to the hydroxyl group in one Ch alkyl chain, Ch-TOTO system exhibits some particular properties. The introduce of functional group can tune ILs properties and promote the design of task-specific ILs.