SEM characterization was performed on commercial and modified membranes to understand the nature of the surface following UDD incorporation. Figure 2 presents the PES FE-SEM images at 20,000× magnification for surface analysis. Figure 2(a) shows the PES's symmetric porous matrix prior to the addition of the UDD solution. When UDDs were added, a cluster formation can be seen imbedded in the porous matrix (Figure 2(b)). These UDD clusters have different sizes, ranging from 0.1 to 10 μm, and are most likely caused by the coupling of C–C bonds between nanoparticles (Popov 2021), van Der Waals forces and electrostatic interactions (Zheng et al. 2009; Wahab et al. 2015). Different from Figure 2(b), the embedded functionalized UDDs (Figure 2(c)) form smaller clusters within the porous matrix. The UDD amount embedded on PES membranes changes when sonication is done to remove the nanoparticles’ excess above the membrane's surface. Table 2 shows how Wt.% of UDD embedded in the membrane is significantly reduced after 1 and 2 min of sonication. For UDD PES and UDD Funct. membranes, Wt.% are 51 and 62% compared to 8.0 and 2.9%, respectively, after sonication is performed for 1 min to remove UDD excess above the membrane.
Table 2

Wt.% of UDD embedded on PES membrane

MembraneWeight (g)UDD Wt.%
PES 0.0696 ± 0.0001 
UDD PES 0.1048 ± 0.0140 51 
UDD PES Funct. 0.1127 ± 0.0013 62 
UDD PES 1 min 0.0751 ± 0.0073 8.0 
UDD PES 2 min 0.0788 ± 0.0062 13 
UDD PES Funct. 1 min 0.0716 ± 0.0004 2.9 
UDD PES Funct. 2 min 0.0712 ± 0.0001 2.4 
MembraneWeight (g)UDD Wt.%
PES 0.0696 ± 0.0001 
UDD PES 0.1048 ± 0.0140 51 
UDD PES Funct. 0.1127 ± 0.0013 62 
UDD PES 1 min 0.0751 ± 0.0073 8.0 
UDD PES 2 min 0.0788 ± 0.0062 13 
UDD PES Funct. 1 min 0.0716 ± 0.0004 2.9 
UDD PES Funct. 2 min 0.0712 ± 0.0001 2.4 
Figure 2

FE-SEM surface porous matrix images of commercial PES (a); UDD modified PES (b); UDD functionalized PES (c). UDD PES and UDD functionalized PES membrane images show UDD particles that are present both on the membrane's surface and inside the porous structure of the membrane. The functionalized UDD membrane shows the particles to be more dispersed throughout the membrane and inside its pores.

Figure 2

FE-SEM surface porous matrix images of commercial PES (a); UDD modified PES (b); UDD functionalized PES (c). UDD PES and UDD functionalized PES membrane images show UDD particles that are present both on the membrane's surface and inside the porous structure of the membrane. The functionalized UDD membrane shows the particles to be more dispersed throughout the membrane and inside its pores.

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