## 3 Results
### Characterization of the Prepared Membranes
SEM  
Morphology of the membranes surface (top and bottom side) and the relative cross-section of the prepared membranes are shown in Figure 3. It is possible to observe that all the investigated membranes exhibited an asymmetric microstructure including a denser skin top-layer, acting as selective barrier, supported on a porous sub-layer. Moreover, the improvement of PAA concentration from 0 wt. % to 8 wt. % increased the surface porosity of the membrane, reduced the thickness of the skin layer, and turned the morphology of the membrane from finger-like to sponge-like. In fact, the neat CA membrane (M0) presented dense surfaces and macrovoids, whereas the presence of PAA led to the preparation of highly porous membrane. The formation of the skin layer is usually caused by the rapid evaporation of volatile solvents (such as acetone) from the top surface of the nascent membrane during the casting. The consequence is the local increasing of the polymer concentration, leading to the generation of a dense skin layer [31; 41]. This dense layer reduced the diffusion of the non-solvent from coagulation bath into polymeric solution resulting in a delayed demixing, leading to the formation of the macrovoids [42]. Figure 2: DSC thermograms of the (**a**) pure PAA polymer and (**b**) of the membranes prepared in this work. The composition of the dope solution is a key factor to modulate the membrane morphology by the affinity between the solvent and the non-solvent and the viscosity of the casting solution [43]. PAA is a hydrophilic polymer, and its blend with CA accelerated the exchange rate of the solvent/non-solvent favouring the formation of finger-like microstructure, as observed for M8 [44]. For M15, the higher amount of PAA increased the viscosity of the casting solution, which delayed the exchange rate of the solvent/non-solvent leading to a sponge-like structure [45]. * Porosity, Pore Size, Contact Angle, Water Content and Pure Water Permeability Measurements of porosity confirmed the outcomes of SEM pictures: the increase of the PAA concentration in the blend raised the total porosity from 44.56% for M0 to 75.6% for M15 (Table 4). On the other hand, the mean pore radius (rm) slightly decreased by increasing the PAA from ca. 13 nm for M0 to ca. 10 nm for M15 (Table 4). The presence of PAA not only affected the membranes morphology but also their chemical-physical properties by improving their hydrophilic character. In fact, the contact angle decreased from 71.55\({}^{\circ}\) for the neat CA membrane (M0) to 37.34\({}^{\circ}\) and 25.04\({}^{\circ}\) for M8 and M15, respectively, (Figure 4). This was mostly due to the enhancement of the \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Membranes** & **Porosity (\%) \(*\)** & **r\({}_{\text{m}}\) [nm] \(*\)** & **Water Uptake** & **L\({}_{\text{p}}\)** \\  & & & **(\%) \(*\)** & **(L m\({}^{-2}\) h\({}^{-1}\) bar\({}^{-1}\)) \(*\)** \\ \hline M0 & 44.58 \(\pm\) 0.2 & 12.92 \(\pm\) 0.02 & 50.64 \(\pm\) 0.12 & 15.51 \(\pm\) 1.2 \\ \hline M8 & 64.50 \(\pm\) 0.4 & 10.13 \(\pm\) 0.02 & 69.87 \(\pm\) 0.24 & 17.30 \(\pm\) 1.4 \\ \hline M15 & 75.65 \(\pm\) 0.7 & 9.65 \(\pm\) 0.03 & 78.23 \(\pm\) 0.1 & 19.98 \(\pm\) 0.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Summary of the CA and CA/PAA blended membranes prepared. Figure 3: SEM images of neat membrane M0 and the blended membrane M8 and M15 with Magnification of 150\(\times\) (cross-section), 1000\(\times\) (top surface) and 5000\(\times\) (bottom surface). hydrophilic sites (carboxylic groups) available in the membranes M8 and M15 and provided by the PAA. Thus, the addition of the PAA facilitates water diffusion through the membrane by improving the hydrogen bonding interactions [46]. In fact, as reported in Table 4, the maximum water uptake (78.2%) was observed for the membrane with the highest PAA amount (M15), whereas the neat CA membrane (M0) showed the lowest water uptake (50.6%).