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.