## 3 Results and Discussion
### Absorption Mechanism through Enthalpy and Sigma Analysis  
Figure 2 contains the sigma profiles for the studied DES components following the primary \(y\)-axis. The \(x\)-axis is the sigma segment charge while the primary \(y\)-axis is the frequency of the segment on the molecule. The secondary \(Y\)-axis is the chemical potential of difluoromethane when interacting with specific charged surfaces represented on the \(x\)-axis, which are represented as a dotted line. Negative chemical potential values correspond to energetically favorable interactions between difluoromethane and a given surface charge. It is evident that the difluoromethane prefers to interact with van der Waals and hydrogen bond accepting surfaces. The parabolic nature indicates repulsion from sufficiently negative or positively charged surfaces with a hydrophobic attribute [23]. The sigma profiles of the HBA and HBD all show large peaks in the non-polar region, with varying peak tail areas in the polarized segments (\(<\!-0.0078\) e/A\({}^{2}\), \(>\!0.0078\) e/A\({}^{2}\)) [36]. This is expected due to the hydrophobic nature of type 5 DES which these components comprise. This compliments the difluoromethane interaction preferences, which explains the relatively low In activity coefficient values witnessed for all solvent combinations as discussed earlier. However, the defining property for why N4 Br, N8 Br, BTACI, and MTOA outperformed the other HBA lies in the surface charge distributions. The four studied HBD (eucalyptrol, polyethylene glycol, camphor, and lidocaine) are also included in Figure 2 and are represented as having remarkably similar sigma profiles to each other. \begin{table}
\begin{tabular}{l c c c c} \hline  & **N4 Br** & **BTACI** & **N8 Br** & **N81 Br** \\ \hline PEG & \(-1.39\) & \(-1.28\) & \(-1.11\) & \(-1.04\) \\ Camphor & \(-1.34\) & \(-1.20\) & \(-1.07\) & \(-1.01\) \\ Lidocaine & \(-1.27\) & \(-1.16\) & \(-1.06\) & \(-1.00\) \\ Eucalyptrol & \(-1.27\) & \(-1.11\) & \(-1.02\) & \(-0.94\) \\ \hline \end{tabular}
\end{table} 
Table 1: In activity coefficients for 1:1 ratio of top performing type 5 DES HBA (columns) and HBD (rows). All computed activity coefficients are available in Figure S1. Table S2 contains surface area charge distribution as a percentage of the total surface area in terms of hydrogen bond donating, accepting, and van der Waals interacting surfaces. This was achieved through the integration of the sigma profile for each respective molecule with limits representing the charge regions of \(<\)\(-\)0.0078 e/A\({}^{2}\) (hydrogen bond donating region), \(>\)0.0078 e/A\({}^{2}\) (hydrogen bond accepting region), and \(-\)0.0078 to 0.0078 e/A\({}^{2}\) (van der Waals interactions region). Following the discovery from the sigma potential plot of difluoromethane, [TETA]Cl and TOPO were the worst performing of the HBA and contained the highest surface area percentage in the hydrogen bond donating region, which supplies a repulsive charge to difluoromethane. However, N4 Br, N8 Br, BTACI, MTOA, camphor, PEG, lidocaine, and eucalypt all lack significant area in the hydrogen bond donating region (\(<\)6%), have the majority of their area in the non-polar region (\(>\)80%), and some area in the favorable hydrogen bond accepting region (6% \(<\) x \(<\) 15%). Table 2 contains the excess enthalpy of interaction computations for 16 combinations of solvents reflecting the results of Section 3.2. This table contains H\({}_{\rm int}\), H\({}_{\rm mf}\), H\({}_{\rm hb}\), and H\({}_{\rm vdw}\) values. As expected from the sigma analysis, the most energy is released through van der Waals interactions, with up to ten times the energetic release from favorable hydrogen bonding. The H\({}_{\rm vdw}\) values are all approximately \(-\)3 and the H\({}_{\rm HB}\) values are all between \(-\)0.3 and \(-\)0.5.