# Nano-Fibrous Networks from Co-Assembly of Amphiphilic Peptide and Polyelectrolyte
## 3 Results and Discussion
As shown in Figure 9A,B, a material is well formed but has a surface punctuated with cavities. These are the result of a rapid interaction between the PSSNa and the PA since the interface seems to have been formed when the PSSNa droplets came in touch with the aqueous layer of PA (Figure 9C), without allowing the time required for these droplets to coalesce in a continuous layer. Although the result is interesting by illustrating how fast are the interactions to yield a solid interface, the material obtained is too fragile for the envisaged application. Finally, when a PSSNa solution was tape-casted on a PVDF support membrane, followed by a spray of the PA solution, a relatively uniform material is obtained (Figure 9D). The imprint left by the droplets is much less present as shown by the cross section of the material. The thickness of the selective layer is 4.5 \(\upmu\)m. Good adhesion is observed between the PVDF support and the self-assembled PA-PSSNa selective layer. The mechanical properties are also better and allowed an AFM analysis which demonstrates the presence of structuring network of fibers as expected (Figure 9E). The diameter of the fibers are of the order of 45 nm. The membrane was then mounted in a dead-end filtration cell and three full pressure cycles (increasing and decreasing) were performed (Figure 10). Relatively linear curves with a low hysteresis between the up and down cycles were observed. The calculated membrane permeability of 10 L\(\cdot\)h\({}^{-1}\cdot\)m\({}^{-2}\cdot\)bar\({}^{-1}\) is moderate, which could be ascribed to the relatively high thickness of the selective layer (4.5 \(\upmu\)m). The slight decrease in flux observed between the filtration cycles can be explained by the electrostatic nature of the interactions between the PA and PSSNa. Indeed, it is possible that a reorganization of the interactions under pressure could be at the origin of this moderate decrease by compressing the selective layer. The pore size of the membrane was estimated from filtration experiments using polyethylene glycol (PEG) of different molecular weights. The solute rejection versus the solute diameter is plotted in Figure 10B. Using the Einstein-Stokes radius of the solute, the mean pore size is considered as the solute diameter that corresponds to a retention of 50%,  
Figure 9: SEM surface pictures of PA-PSSNa self-standing membranes made by tape-casting of a PA solution followed by spray-coating of PSSNa solution (**A,B**) as illustrated in (**C**). SEM pictures of cross section (**D**) and AFM (**E**) of the PVDF-supported membrane. whereas the geometric standard deviation is obtained from the ratio of solute diameter at retentions of 84.13% and 50% [34]. The membrane material falls into the ultrafiltration range with a pore radius of 7.61 \(\pm\) 1.90 nm. Based on these values, the pore size distribution was plotted in Figure 10B by using a log-normal model [35].To the best of our knowledge, this is the first example of a composite filtration membrane formed from water-soluble polyelectrolytes structured by a self-assembling peptide.