Figure 3. The characterization results of the Janus membrane fabricated by selective infiltration of PTFE on the hydrophilic PVDF supports. (a) Comparison of nitrogen flow rate into the pristine PVDF with those of Janus membranes made at different deposition pressures (300-1200 mTorr). (b) Water contact angle on the top (coated) and the bottom surface of Janus membranes fabricated at different deposition pressures (300-1200 mTorr). Here, the water contact angle on the bottom (uncoated) surface of hydrophilic supports is zero. (c) The contact angle of water and ethylene glycol droplets on the top and bottom surface of the Janus membranes. Here, to make the Janus membrane, the PTFE deposition was performed at 1200 mTorr for five minutes. (b) Water and ethylene glycol droplets on a Janus membrane floating on water while oil droplet is in contact with the hydrophilic (bottom) surface immersed in water. Here, to make the Janus membrane, the PTFE deposition was performed at 900 mTorr for five minutes. To investigate the effectiveness of the deposited PTFE layer in maintaining an air gap between two liquid streams, we examined our fabricated Janus membranes in direct contact membrane distillation (DCMD) and desalinate a synthetic water solution containing 35 g/L NaCl.17,35 Figure 4 shows the DCMD performance of the Janus membrane for 60 minutes. As shown, the salt rejection and water flux remained stable during this experiment. This observation confirms the effectiveness of fabricated schemes in the development of Janus membranes. The measured liquid entry pressure (LEP), presented in Section S6 of Supporting Information, further confirms that the fabricated Janus membranes have high wetting resistance. Using our developed approach, we further fabricated Janus membranes on a few hydrophilic substrates such as cellulose acetate and carbon nanotube-polyvinyl alcohol (CNT-PVA) composite. The images of Janus CNT-PVA composite and DCMD performance of the Janus cellulose acetate membrane are shown in Section S7, Supporting Information. Movie S3, Supporting Information, also shows the impact of water droplets on the top surface of Janus CNT-PVA composite.