## 3 Results
### Permeations and Selectivity of Membranes  
In the application of CPC, the transmission rate of water vapor should be higher than 2000 g m\({}^{-2}\)-day\({}^{-1}\)[3]. As shown in Table 3, all the synthetic membranes M1-M6 possessed a WVTR value greater than 2000 g m\({}^{-2}\)-day\({}^{-1}\), meeting the CPC requirement. The sodium sulfonate groups within the membrane has satisfactory affinity for water molecules, so it can promote water diffusion and improve the moisture permeability of the membrane by increasing the hydrophilicity.  
The vapor permeation (VP) of DMMP is shown in Figure 10 and Table 3. When the addition ratio of GO-SSS increased from 0% to 2%, the DMMP vapor permeation decreased first and then increased. The selectivity between water vapor and DMMP is displayed in Figure 11. When the addition ratio of GO-SSS is from 0% to 0.5%, the selectivity gradually increases from 118 to 125. The composite membrane shows higher selectivity than the  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Sample** & \begin{tabular}{c} **VTR of Water** \\ **(g m\({}^{-2}\) 24 h\({}^{-1}\))** \\ \end{tabular} & \begin{tabular}{c} **VP of Water** \\ **\(\times\) 10\({}^{-5}\)(mol s\({}^{-1}\) m\({}^{-1}\))** \\ \end{tabular} & \begin{tabular}{c} **VP of DMMP** \\ **(mol s\({}^{-1}\) m\({}^{-1}\))** \\ \end{tabular} & \begin{tabular}{c} **VP of CEPS** \\ **\(\times\) 10\({}^{-9}\) (mol s\({}^{-1}\) m\({}^{-1}\))** \\ \end{tabular} & \
\begin{tabular}{c} **Selectivity** \\ **(Water/DMMP)** \\ \end{tabular} &
\begin{tabular}{c} **Selectivity** \\ **(Water/CEPS)** \\ \end{tabular} \\ \hline M1 & \(3307\pm 75\) & \(255.23\pm 5.76\) & \(2.15\pm 0.18\) & \(0.13\pm 0.01\) & \(118.71\pm 7.26\) & 1963.31 \(\pm\) 106.72 \\ M2 & \(3235\pm 64\) & \(243.36\pm 4.82\) & \(2.03\pm 0.12\) & \(0.12\pm 0.02\) & \(119.88\pm 4.71\) & 2028.00 \(\pm\) 297.83 \\ M3 & \(2902\pm 55\) & \(210.89\pm 4.03\) & \(1.73\pm 0.06\) & \(0.10\pm 0.01\) & \(121.90\pm 1.89\) & 2108.90 \(\pm\) 170.59 \\ M4 & \(2622\pm 52\) & \(183.78\pm 3.63\) & \(1.46\pm 0.08\) & \(0.08\pm 0.01\) & \(125.88\pm 4.41\) & 2297.25 \(\pm\) 241.78 \\ M5 & \(2593\pm 51\) & \(176.74\pm 3.51\) & \(1.67\pm 0.11\) & \(0.12\pm 0.02\) & \(105.83\pm 4.87\) & 1472.83 \(\pm\) 216.22 \\ M6 & \(2652\pm 56\) & \(175.66\pm 3.74\) & \(1.89\pm 0.13\) & \(0.14\pm 0.02\) & \(92.94\pm 4.41\) & 1254.71 \(\pm\) 152.53 \\ \hline \hline \end{tabular}
\end{table}
Table 3: VTR of water; VP of water, DMMP, and CEPS; selectivity between water and DMMP; and selectivity between water and CEPS of M1–M6 membranes.  
Figure 9: Typical stress–strain curves of M1–M6 membranes.  
PSSA membrane (80) and the sulfonated poly(styrene-isobutylene-styrene) membrane (35) reported elsewhere [13; 18], suggesting the role of GO-SSS in the improvement of membrane selectivity of water/DMMP.  
The vapor permeability (VP) of CEPS is shown in Figure 10 and Table 3. CEPS vapor permeability first increased and then decreased with GO-SSS dosage. When the addition ratio of GO-SSS is 0.5%, the selectivity gradually increases from 1967 to 2293. This shows that the addition of GO-SSS can significantly improve the selectivity of water/CEPS, which is much higher than the PSSA membrane (1500) and Nafion membrane (400) [13].