In order to clarify if the employment of a hydrophilic substrate would offer any advantages over the relatively hydrophobic substrate, both the TFC membranes with the PAN-O substrate and the PAN-A substrate modified by PAH were further characterized using FO processes. The water flux was measured employing two different membrane orientations; that is, the active layer was exposed to the draw solution (AL-DS) or the feed solution (AL-FS). Despite the orientation difference (i.e., different degree of ICP45,46), the TFC-PAH yielded a water flux of ~26 LMH, which was nearly twofold greater than the water flux of ~13 LMH for the TFC-O as shown in Figure 9a. Therefore, it is reasonable to infer that the wettability of the substrate network could have substantial impact on the ICP. The calculation results of FO efficiency are shown and compared in Figure 9b. It is evident that the FO efficiency of the TFC-PAH was almost doubled compared with that for the TFC-O. However, it is quite challenging to unravel the mechanisms accounting for the complex transport phenomena in the substrate, especially when the effects of the wettability of the polymeric network cannot be ignored. A possible explanation is that the variation in the wettability could significantly change the topological substructures of the network47,48 and thereby give rise to different paths effective for the fluid flow and the solute flux.