Figure 6. AFM (2D and3D) images of the surface roughness of the PTFE membrane (a, b) and PES membrane (c, d).
The solution hydrophilicity is another property impacting the interfacial nucleation. As shown in Figure 7, PTEF and PES membrane surface had diverse surface contract properties with the thiourea aqueous solution. The contact angle of the PTFE hollow fiber membrane is around 108°, and the contact angle of the PES hollow fiber membrane is around 83°. The increasing concentration of thiourea (from 3 wt% to 12 wt%) had almost no influence on the contact angle, which ensure a stable nucleation control performance under wide feed solution concentration.