Physiochemical Properties and Molecular Dynamics Simulations of Phosphonium and Ammonium Based Deep Eutectic Solvents

Deep eutectic solvents (DES) are considered as second-generation ionic liquids and are used in many applications such as separation, extraction and electrochemistry. In the current work, a set of four DES is synthesized by mixing a hydrogen bond donor (HBD) (ethylene glycol/glycerol) with a quaternary ammonium or phosphonium salt or the hydrogen bond acceptor (HBA). Here the HBA, namely methyltriphenylphosphonium bromide and tetrabutylammonium bromide (TBAB), were mixed with the HBD in a molar ratio of 1:4. Fourier transform infrared and thermogravimetric analysis analysis were then carried out to understand the functional groups along with their thermal stability. NMR analysis was also used to validate the molar ratio of 1:4 in solution. Thereafter, the four DESs were simulated with molecular dynamics simulations to evaluate and measure the pure component properties of these solvents at room temperature. Thermodynamics insights such as non-bonded interaction energies, hydrogen bonds, coordination number and radial distribution functions were also discussed to understand their atomistic interactions involved in the eutectic mixtures.