## 2 Results and Discussion
### Characterization
#### 2.3.3 XRD Analysis  
XRD traces of PDMAEMA-CPTCD and SPDMAEMA-8 were shown in Figure 7. The diffraction peaks of PDMAEMA-CPTCD and SPDMAEMA-8 are formed by the amorphous diffuse peak, suggesting that they are completely amorphous polymers.  
Figure 6: IR spectra of PDMAEMA-CPTCD (a) and SPDMAEMA-8 (b).  
CO\({}_{2}\) Separation Performance of the Blending Composite Membranes with Different Cs/SPDMAEMA-8 Volume Ratios under the Wet Condition  
Figure 8 showed the performance of the blending composite membranes with different Cs/SPDMAEMA-8 volume ratios (Cs:SPDMAEMA-8 = 8:0, 7:1, ;6:2, 4:4, 2:6, 1:7) in different pressure: (a) CO\({}_{2}\) permeation rate; (b) N\({}_{2}\) permeation rate; (c) ideal selectivity of CO\({}_{2}\) over N\({}_{2}\). As illustrated in Figure 8, all blending composite membranes with different Cs/SPDMAEMA-8 volume ratios have the same trend as the feed gas pressure changes. With increasing feed gas pressure, CO\({}_{2}\) permeation rate drops rapidly at a relatively low pressure (7.5-22.5 cmHg) and then decreases gently at a higher pressure (22.5-37.5 cmHg). This is due to the increment pressure increasing the concentration of CO\({}_{2}\) in the membrane, which results in facilitated transport reversible reaction the impact of the control. In comparison with CO\({}_{2}\), the N\({}_{2}\) permeation rate decreases slightly and does not change obviously when the feed gas pressure changes. This is because N\({}_{2}\) follows the dissolution diffusion mechanism.  
For the pure Cs membrane (2.0 wt % Cs casting membrane solution), CO\({}_{2}\) permeation rate and ideal selectivity of the blending composite membrane both have a great improvement, but the N\({}_{2}\) permeation rate does not significantly change when increasing the content of SPDMAEMA-8. For instance, at a feed gas pressure of 37.5 cmHg and 30 \({}^{\circ}\)C, the pure Cs membrane had a CO\({}_{2}\) permeation rate of 2.64 \(\times\) 10\({}^{-5}\) cm\({}^{3}\) (STP) cm\({}^{-2}\)-s\({}^{-1}\)-cm\(\cdot\)Hg\({}^{-1}\) and an ideal CO\({}_{2}\)/N\({}_{2}\) selectivity of 2.9, while the blinding composite membrane (Cs:SPDMAEMA-8 = 4:4) had a CO\({}_{2}\) permeation rate of 8.54 \(\times\) 10\({}^{-4}\) cm\({}^{3}\) (STP) cm\({}^{-2}\)-s\({}^{-1}\)-cm\(\cdot\)Hg\({}^{-1}\) and an ideal CO\({}_{2}\)/N\({}_{2}\) selectivity of 35.2. This may be because star PDMAEMA can offer a larger free volume due to its unique properties compared with their linear analogues. Moreover, increasing the content of star polymer will cause increment of the amount of effective CO\({}_{2}\) facilitated carriers in the membrane. However, when Cs:SPDMAEMA-8 equals 1:7, the blinding composite membrane had a bad mechanical strength and was easy to break with the increasing pressure so that the blinding composite lost the separation performance.  
Figure 7: The XRD traces of PDMAEMA-CPTCD and SPDMAEMA-8.  
Figure 8: The permeability of the blinding composite membranes at different Cs/SPDMAEMA-8 volume ratios (**A**) CO\({}_{2}\) permeation rate (**B**) N\({}_{2}\) permeation rate (**C**) Ideal Selectivity of CO\({}_{2}\) over N\({}_{2}\) (Pure humidified gas, 30 \({}^{\circ}\)C).