## 3 Results and Discussion
### Effects of Change in Composition of DES  
Table 3 shows the results of the compositional analysis. Due to the nature of the ln activity coefficient procedure being performed at a composition of 1:1, the optimal ratio for affinitive interactions will be studied. The ln activity coefficient of difluoromethane was computed for each solvent combination in six different compositions: 1:0, 3:1, 2:1, 1:1, 1:2, and 1:3 being HBA:HBD. Nearly all DES eutectic compositions are found in the range from 1:1 to 1:3 HBA top HBD [29; 37]. Thus, the studied compositional ranges reflect this commonality. It is evident that the pure form of HBA has the lowest ln activity coefficients, which indicates a most favorable interaction with difluoromethane, and N4 Br (\(-\)1.61) having the best of the four. However, the HBA have relatively high melting points compared to their DES form. To use the quaternary ammonium salts alone would require temperatures of approximately 100 \({}^{\circ}\)C for them to reach their melting points, which is counter conducive to gas solubility compared to room temperature absorption. Thus, the lowest possible concentration of HBD is recommended to create a room temperature solvent for difluoromethane uptake. Furthermore, the ranking of HBD follows PEG (\(-\)1.39), camphor (\(-\)1.34), lidocaine (\(-\)1.27), and eucalypt (\(-\)1.27) for producing the lowest ln activity coefficients when paired with N4 Br. This trend holds for pairings with all four HBA. This trend follows the findings of the sigma analysis where the ranked components follow the favorable charge distributions that induce favorable difluoromethane interaction.  
\begin{table}
\begin{tabular}{l l c c c c} \hline \hline \multirow{2}{*}{**HBD**} & \multirow{2}{*}{**Property**} & **N4 Br** & **BTACI** & **N8 Br** & **MTOA** \\  & & **(k/mol)** & **(k/mol)** & **(kJ/mol)** & **(kJ/mol)** \\ \hline PEG & H\({}_{\rm int}\) & \(-\)1.15158 & \(-\)1.12681 & \(-\)1.15158 & \(-\)1.12756 \\ PEG & H\({}_{\rm mf}\) & 1.4377 & 1.44851 & 1.4377 & 1.42068 \\ PEG & H\({}_{\rm bb}\) & \(-\)0.40207 & \(-\)0.43892 & \(-\)0.40207 & \(-\)0.37627 \\ PEG & H\({}_{\rm vdw}\) & \(-\)3.13471 & \(-\)3.08391 & \(-\)3.13471 & \(-\)3.11947 \\ Camphor & H\({}_{\rm int}\) & \(-\)1.12736 & \(-\)1.10647 & \(-\)1.15158 & \(-\)1.11496 \\ Camphor & H\({}_{\rm mf}\) & 1.45191 & 1.45861 & 1.4377 & 1.40033 \\ Camphor & H\({}_{\rm bb}\) & \(-\)0.39266 & \(-\)0.42837 & \(-\)0.40207 & \(-\)0.33878 \\ Camphor & H\({}_{\rm vdw}\) & \(-\)3.13412 & \(-\)3.0842 & \(-\)3.13471 & \(-\)3.12401 \\ Eucalypt & H\({}_{\rm int}\) & \(-\)1.14948 & \(-\)1.13061 & \(-\)1.12736 & \(-\)1.09226 \\ Eucalypt & H\({}_{\rm mf}\) & 1.46866 & 1.47271 & 1.45191 & 1.41422 \\ Eucalypt & H\({}_{\rm bb}\) & \(-\)0.41278 & \(-\)0.4479 & \(-\)0.39266 & \(-\)0.33038 \\ Eucalypt & H\({}_{\rm vdw}\) & \(-\)3.15286 & \(-\)3.10292 & \(-\)3.13412 & \(-\)3.1236 \\ Lidocaine & H\({}_{\rm int}\) & \(-\)1.12756 & \(-\)1.1175 & \(-\)1.14948 & \(-\)1.11091 \\ Lidocaine & H\({}_{\rm mf}\) & 1.42068 & 1.4228 & 1.46866 & 1.42843 \\ Lidocaine & H\({}_{\rm bb}\) & \(-\)0.37627 & \(-\)0.40817 & \(-\)0.41278 & \(-\)0.3468 \\ Lidocaine & H\({}_{\rm vdw}\) & \(-\)3.11947 & \(-\)3.07964 & \(-\)3.15286 & \(-\)3.14005 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Enthalpy of mixing analysis where H\({}_{\rm int}\) is the excess enthalpy of interaction, H\({}_{\rm mf}\) is the enthalpic contribution due to misfitting of sigma segments, H\({}_{\rm bb}\) is the enthalpic contribution from hydrogen bonding, and H\({}_{\rm vdw}\) is the enthalpic contribution from van der Waals interactions. All the enthalpies are presented as kJ/mol.