## 3 Results and Discussion
### Sorption Behaviour
Though the results for the desorption run in **P\({}_{9}\)IL\({}_{6}\)Zn\({}_{0}\)** and the adsorption run in **P\({}_{9}\)IL\({}_{6}\)Zn\({}_{1}\)** align well with the calculated values of DMM. These anomalies give an impression that some measurement points at lower pressure range might have had insufficient time to equilibrate, affecting their accuracy. However, the reason for this unusual curve shape is not completely clear, and is most likely related to a low measurement sensitivity or a low signal-to-noise ratio of the sorption instrument at low pressures and at very low amounts of sorption. There is no likely physical mechanism to explain such a curve shape, and calculations of the characteristic times based on the particle size and diffusion coefficient indicate that the total measurement time is sufficient to reach equilibrium. Nevertheless, the desorption curves should give a reliable range of the sorption behavior. Overall, the solubility selectivity decreases with increasing gas pressure and reaches steady state at the maximum sorption capacity of the material (Figure 4). The CO\({}_{2}\) and N\({}_{2}\) adsorption in the FFV positively affect the CO\({}_{2}\)/N\({}_{2}\) solubility selectivity of **P\({}_{9}\)IL\({}_{6}\)Zn\({}_{9}\)** in the low pressure region (\(<2\) bar). Additionally, [PERSON]'s sorption contribution enhances the solubility selectivity for **P\({}_{9}\)IL\({}_{6}\)Zn\({}_{9}\)** by at least 40 % at a higher pressure range (\(>\)2 bar) in the region controlled by [PERSON] sorption model (Table 2). Similar behavior is observed for the pure PIL **P\({}_{9}\)IL\({}_{0}\)Zn\({}_{0}\)** which reveals a smaller contribution of Langmuir's sorption. The likely diminishing of the FFV content in the **P\({}_{9}\)IL\({}_{6}\)Zn\({}_{0}\)** and **P\({}_{9}\)IL\({}_{6}\)Zn\({}_{1}\)** leads to approximately 30 % and 50 % lower \(S_{\text{CO}_{2}}\)/\(S_{\text{N}_{2}}\) for **P\({}_{9}\)IL\({}_{6}\)Zn\({}_{0}\)** and **P\({}_{9}\)IL\({}_{6}\)Zn\({}_{1}\)**, respectively. Additionally, their performances in terms of \(\alpha_{S}\), \(\alpha_{D}\) and \(\alpha_{P}\) remained nearly constant over the whole range of pressures investigated. The diffusivity selectivity remains nearly constant with increasing gas pressure for all membranes. **P\({}_{9}\)IL\({}_{6}\)Zn\({}_{0}\)** and **P\({}_{9}\)IL\({}_{6}\)Zn\({}_{1}\)** show almost no \(D_{\text{CO}_{2}}\)/\(D_{\text{N}_{2}}\), as the composite material contains more than 37.5 wt % of IL liquid (Table 1). The plasticization of the polymer by the IL favors the diffusivity of both gases through the membrane. Although the **P\({}_{9}\)IL\({}_{6}\)Zn\({}_{9}\)** contains about 25 wt % of IL (Table 1), it has similar diffusion selectivity to the pure PIL (**P\({}_{9}\)IL\({}_{0}\)Zn\({}_{0}\)**). This phenomenon indicates the excess amount of Zn[Tf\({}_{2}\)N]\({}_{2}\) within the composite disrupts the IL domains and hinders the diffusion. Normally, N\({}_{2}\) diffusion is somewhat slower than CO\({}_{2}\) diffusion, as a result of its slightly larger effective diameter. Only in rubbers or soft materials is CO\({}_{2}\) diffusion much closer to that of N\({}_{2}\) or even up to ca. 30 % slower than N\({}_{2}\). Based on the DSC results and the glassy state of **P\({}_{9}\)IL\({}_{0}\)Zn\({}_{0}\)**, the low CO\({}_{2}\)/N\({}_{2}\) diffusion  
Figure 4: CO\({}_{2}\)/N\({}_{2}\) ideal solubility (**a**) and diffusivity (**b**) selectivities derived from single gas sorption experiments at 20 \({}^{\circ}\)C. The solid curves provide guides for eyes. selectivity is opposed to what one would expect [74] and further strengthens the hypothesis of CO2 chemisorption in the PIL, or otherwise shows interaction, which may restrict diffusion of CO2[75]. Figure 5 depicts permeability selectivity (\(P_{\text{CO2}}/\text{N}_{\text{2}}\)) as the product of ideal solubility and diffusivity selectivities (ESI Equation (8)). The permeability selectivity predicts considerably higher values for the composites containing Zn2 salt in comparison to PIL and PIL/IL materials.