## 5 Characterization of Membranes
### Morphology Analysis  
Figures 6 and 7 display SEM images of surface and cross section of pristine membranes and PVDF-g-PHEA included PVDF membranes. Morphology analysis is important to analyze the structure of membranes in detail. Surface and cross section of membranes were magnified at 50,000 and 1000 times, respectively. As shown in Figures 6 and 7, numerous pores were observed in the surface of all membranes including PVDF pristine membranes and PVDF membranes containing PVDF-g-PHEA. When comparing PVDF membranes containing PVDF-g-PHEA with PVDF pristine membranes to observe the cross-sectional image as shown in Figures 6 and 7, the blending of 0.9% PVDF-g-PHEA additive (B-2) led to formation of membrane cross section with deep and macrovoid holes in comparison with no additive (B-1). 0.6% PVDF-g-PHEA (A-2) caused macrovoid holes in the lower side in comparison with 9.5% PVDF pristine membrane (A-1). As observed in the top layer of the membrane, PVDF membrane blended with 0.9% PVDF-g-PHEA additive absolutely possessed thinner top layer than 10% PVDF pristine membrane. This phenomenon was observed when hydrophilic material, PVDF-g-PHEA additive, was combined with PVDF to fabricate membranes. It may be attributed to instantaneous demixing process in water bath during phase inversion due to hydrophilic PVDF-g-PHEA in PVDF casting solution. There are numerous relative papers such as [2,26]. According to the SEM images of surface of membranes and cross section of membranes, as the concentration of  
Figure 5: Pore Size Distribution of (**a**) A-1; (**b**) A-2; (**c**) B-1 and (**d**) B-2 membranes. PVDF-g-PHEA was increased, macrovoid holes were observed in the lower side and top layer of the membrane became thinner. Figure 6: SEM images: surface of **(a)** A-1; **(b)** A-2; **(c)** B-1, and **(d)** B-2 membranes. Figure 7: SEM images: cross-section of **(a)** A-1; **(b)** A-2; **(c)** B-1 and **(d)** B-2 membranes. Figures 8 and 9 indicate permeate flux of all membranes during filtration of 6 and 20 ppm HA solution. To demonstrate comparable difference in permeate flux, the pore size of membranes was made similarly, respectively [17]. Generally, the PVDF membranes blended with PVDF-g-PHEA (A-2 and B-2) had faster final permeate flux (\(J\)) than PVDF pristine membranes (_i.e._, A-1 and B-1). The reason that the initial fluxes (\(J_{0}\)) of A-2 and B-2 were slower than those of A-1 and B-1 is because pore size of PVDF membranes blended with PVDF-g-PHEA was smaller than that of PVDF pristine membranes as shown in Table 2. In other words, A-1 and B-1, with larger pore size than the A-2 and B-2, showed higher initial permeate flux according to Hagen-Poiseuille equation (see Table 2). Hargen-Poiseuille equation represents that permeate flux is proportional to 4 times the pore size [17]. However, despite the A-2 and B-2 membrane having lower initial flux and smaller pore size, reversal phenomenon was observed in permeate flux as time passed. After constant time passed, the final fluxes of A-2 and B-2 were higher than those of A-1 and B-1. To be specific, even though initial fluxes for A-1, A-2, B-1, and B-2 membranes were 312.08, 310.15, 287.30, and 286.01 LMH at 6 ppm HA solution, the final fluxes for A-1, B-1, A-2 and B-2 were 131.45, 137.18, 133.61, and 144.98 LMH at 6 ppm HA solution after 240 min, respectively. That is, the difference of the final fluxes between PVDF membranes blended with PVDF-g-PHEA and PVDF pristine membranes were 5.73 and 11.37 LMH at 6 ppm HA solution, respectively. In addition, initial fluxes of A-1, A-2, B-1, and B-2 membranes were 289.43, 279.95, 264.53, and 260.92 LMH at 20 ppm HA solution, respectively. At 240 min, the final fluxes of A-1, B-1, A-2 and B-2 were 104.92, 111.48, 105.42 and 116.99 LMH at 20 ppm HA solution, respectively. This means that the difference of the final fluxes between PVDF membranes blended with PVDF-g-PHEA and PVDF pristine membranes were 5.73 and 11.37 LMH at 6 ppm HA solution, respectively.