Noura Dawass

5.3. R ESULTS AND DISCUSSION 5 101 rected using the method proposed by Gaungly and van der Vegt [167] . The RDFs were numerically integrated to obtain KBIs of small subvolumes G V αβ (Eq. (1.25) ). To estimate KBIs in the thermodynamic limit, the linear range of the scaling of LG V αβ with L was used. For more details on the computations of the KBIs, the reader is referred to chapter 5. Using KBIs, thermodynamic factors, and partial molar volumes were computed. All simulations were carried out at 343.15 K and 1 atm. For NPT and NV T ensembles, temperature and pressure were maintained using the Nosé-Hoover thermostat and barostat with coupling constants of 0.1 ps and 1 ps, respec- tively [22] . Long range electrostatic interactions between charged species were calculated based on the particle-particle, particle-mesh (pppm) solver with a rel- ative precision of 10 − 6 . The cut-off radius was set to 12 Å, for both the Lennard- Jones (LJ) and the real-space part of Coulombic potentials. LJ parameters be- tween the dissimilar species were determined based on the Lorentz-Berthelot mixing rules [23] . Equations of motions were integrated using the Verlet algo- rithmwith a time step of 1 fs. Standard deviations in the transport properties and KBIs were computed based on 10 and 25 independent simulations, respectively. Each independent simulation started from a different initial configuration. 5.3. R ESULTS AND DISCUSSION 5.3.1. K IRKWOOD –B UFF I NTEGRALS OF UREA – CHOLINE CHLORIDE BSBSB MIXTURES Figure 5.1 presents the RDFs of urea–urea, urea–ChCl and ChCl–ChCl interac- tions at various molar rations of ChCl to urea. In Figure 5.1, it is shown that the position of the first peak of all RDFs remains unchanged with composition. How- ever, the addition of urea to the system has an effect on the height of the first peak, especially for urea–ChCl and ChCl–ChCl distances. Figure 5.1 (a) shows that urea–urea distances remain relatively unchanged with increasing the molar ratio of urea to ChCl. Figures 5.1 (b) and 5.1 (c) show that the height of the first peak of the g ( r ) of urea–ChCl and ChCl–ChCl decreases with increasing molar ratios of urea to ChCl. This indicates weakening of interactions between pairs of urea–ChCl and ChCl–ChCl. The RDFs shown in Figure 5.1 are used to compute KBIs of urea and ChCl at various molar compositions. In Figure 5.2, KBIs in the thermodynamic limit for pairs of urea–urea, ChCl–urea, and ChCl–ChCl at 343.15 K and 1 atm are shown as a function of the mole fraction of urea. The reader should note that in Fig- ure 5.2 as well as in the following figures we report properties as a function of the mole fraction defined in Eq. (5.1) . KBIs of urea–urea pairs are affected the most by the increase of the urea content. Figure 5.2 shows that the values of G urea − urea