## 3 Results and Discussion  
### The Impact of FS Blending on the Membrane Properties  
The surface morphology of the fabricated membranes was probed using SEM, and the obtained micrographs are shown in Figure 3. Cross-sectional images are shown in Figure S1 (Supporting Information). The results illustrate that all membranes were porous and that the FS particles were not homogeneously distributed on the surface of the membranes, but rather were agglomerated. The extent of agglomeration increased as the FS amount in the membrane increased, which can be attributed to the effect the FS additives have on increasing the viscosity of the casting fluid during the fabrication procedure. Moreover, the sizes of the pores were variant, suggesting that variable amounts of FS could result in variable speeds of nucleation distributed within our as-fabricated PVDF polymer layers. Furthermore, the development of the randomly distributed macropores within our membranes could be attributed to the effects of the rapid intrusion of DI within the skin layer of the PVDF membranes [1]. The images probed at lower magnifications suggest that the structure of the membranes was consistent,  
Figure 2: Schematic of the experimental setup illustrating the data acquisition and the connections of the device. and a good degree of reproducibility was achieved throughout our fabrication process. Randomly distributed dark regions across all the membrane structures suggest that the membranes follow the typical distinctive vapor-induced phase separation (VIPS) membrane characteristics, resulting in the accumulation of pores [2]. The results confirm that the addition of the FS particles had no effect on the VIPS characteristics resembled by membranes fabricated with pure PVDF. An excessively hydrophilic membrane can result in flooding, whilst an excessively hydrophobic membrane can interfere with the penetration of the water meniscus through the pores; therefore, a carefully designed wettability is critical to facilitate efficient mass transport from the water film into the pores of the bulk of the membrane, and thus ensure enough replenishment of water from the water film into the pores. Therefore, we performed wettability investigations, as shown in Figure 4a. The results show that the PVDF membrane (with no FS additives) resembled a contact angle of 95.5\({}^{\circ}\), which decreased when small amounts of FS were added (92.5\({}^{\circ}\) and 92.9\({}^{\circ}\) for the PVDF-FS3 and PVDF-FS4 membranes, respectively), and increased when larger amounts of FS were added (109\({}^{\circ}\) and 113.5\({}^{\circ}\) for the PVDF-FS5 and the PVDF-FS7 membranes, respectively). PVDF-FS3 and the PVDF-FS4 membranes resembled similar contact angles, which were the lowest as compared to all other membranes, whilst the PVDF-FS7 resembled the highest contact angle, respectively, and could be attributed to the effect of the FS additive on the structure of the membrane. It is noteworthy here that these results indicate that FS has no effect on the membrane wettability at concentrations of 4% and below. The slight dip in contact angle seen when moving from pristine PVDF to 3 and 4% FS could be due to small changes in the membrane structure during phase inversion since these dips are less than 5% different from the pristine PVDF contact angle. The pore sizes of fabricated membranes are of primary interest because the pores are the driveway paths in which evaporation flux occurs. Moreover, it has been reported in the literature that a higher rate of mass transfer occurs at the edges of the pores rather than their middle regions, as suggested by the perimeter effect phenomenon [3; 4], suggesting that smaller pore sizes can drive a higher rate of evaporation, as shown in the literature via mathematical modeling approaches [31]. Figure 3: SEM images of the fabricated membranes. The results show that the FS particles agglomerated more as the amount of FS content added increased.