# Novel Janus Fibrous Membranes with Enhanced Directional Water Vapor Transmission
## 3 Results and Discussion
### Chemical Characterization and Wettability of As-Prepared Membranes  
The Fourier transform infrared spectroscopy (FTIR) was used to characterize the chemical compositions of the PU/ CA Janus electrospun nanofibroma membrane, as well as the solvents (DMF, THF, acetone) that dissolve the electrospun polymers. FTIR was carried out in the range of 400 cm\({}^{-1}\)-4000 cm\({}^{-1}\) to analyze and confirm the presence of functional groups [32]. The absorption band of DMF at 1687 cm\({}^{-1}\) corresponded to the stretching vibration of the C=O vibration [33]. The peak at 1071 cm\({}^{-1}\) can be assigned to the THF alicyclic ether (C-O-C) stretching vibration [34]. The band  
Figure 3: SEM images and statistic average diameters of PU and CA fibrous membrane. The concentrations of both PU and CA electrospun solution are 12.5 wt %, respectively. (**a–d**) SEM images of PU-6G, PU-8G, PU-10G, and PU-12G electrospun fibrous membranes. The statistic average fiber diameters (AD) are 380 nm, 669 nm, 1090 nm, and 1110 nm, respectively (Bar: 2 \(\mu\)m). (**e–h**) SEM images of CA-6G, CA-8G, CA-10G, and CA-12G electrospun fibrous membranes. The AD are 225 nm, 228 nm, 340 nm, and 354 nm, respectively. around 1715 cm\({}^{-1}\) was the characteristic peak of acetone, which can be attributed to the stretching vibration peak of the C=O group [35]. The peaks at 1050 cm\({}^{-1}\), 1232 cm\({}^{-1}\), 1369 cm\({}^{-1}\), and 1743 cm\({}^{-1}\) of the CA membrane spectra can be assigned to the stretching vibrational peak of the C-O skeleton in ether group, stretching vibration of C-O-C bond, stretching vibration peak of C-CH\({}_{3}\), and the stretching vibration of the C=O group, respectively [36; 37; 38]. Moreover, there were no characteristic peaks at 1687 cm\({}^{-1}\) and 1715 cm\({}^{-1}\), indicating that there was no DMF and acetone solvent residues in the as-prepared CA electrospun nanofibrous membrane. By analyzing the FTIR characterization of electrospun PU fibrous membrane, it was found that a strong peak appeared at 3328 cm\({}^{-1}\), representing the N-H stretching vibration. The peak at 2929 cm\({}^{-1}\) was the asymmetric vibrations of the -CH\({}_{2}\) groups. Since the C=O stretching vibration of the urethane bonds, a medium strong characteristic peak appeared at 1726 cm\({}^{-1}\). The absorption band around 1529 cm\({}^{-1}\) was ascribed to the deformation vibration of N-H bonds in the urethane groups from amide II. The peaks at 1221 cm\({}^{-1}\) was corresponded to the stretching vibration of the C-N bonds. The bands at 1163 cm\({}^{-1}\) and 1068 cm\({}^{-1}\) represented the stretching vibration of the C-O-C groups [38; 39]. In addition, there were no characteristic peaks at 1687 cm\({}^{-1}\) and 1071 cm\({}^{-1}\) which demonstrated that there were no residues of DMF and THF in the PU electrospun nanofibrous membrane. Comparing the FTIR spectrum of both sides of the Janus membrane and the pure PU, CA fibrous membranes, it was found that the spectrum of the PU side of the Janus membrane and the PU fibrous membrane were basically consistent, and the CA characteristic peak was not shown in the PU side of the Janus membrane spectrum. However, the spectrum of the CA side of the Janus membrane not only shows the spectrum of CA fibrous membrane, but also shows the characteristic peak of PU fibrous membrane (at 3328 cm\({}^{-1}\), 2929 cm\({}^{-1}\), 1529 cm\({}^{-1}\), and 1163 cm\({}^{-1}\) in Figure 4a). This phenomenon may be caused by the thicker PU layer and the thinner CA layer. Such analysis and characterizations proving that a free standing hydrophobic/hydrophilic PU/CA Janus fibrous membrane with no solvent residues was successfully prepared. To verify the wettability of the composited two layers of the Janus membrane, water contact angles (WCA) are tested. Figure 4b,c exhibits the water contact angles of the PU and CA fibrous membranes. A water droplet about 3 \(\mu\)L is allowed to contact the surface of all samples.