# Nano-Fibrous Networks from Co-Assembly of Amphiphilic Peptide and Polyelectrolyte
## 3 Results and Discussion
However, in the presence of an excess of polymer (R\({}_{+/-}<1\)), inhomogeneity can be observed with the appearance of accumulation zones of the polymer which no longer integrate the PA network. The change in the average fibril diameter as a function of R\({}_{+/-}\) (Figure 4G) shows a plateau regime in the presence of a polymer excess followed by a size decrease while increasing the PA amount in the mixture. It seems logical to observe an increase in the size of the fibrils when increasing the polymer concentration if we consider that the polymer coils between the PA micelles and aggregates them. However, beyond a critical threshold (R\({}_{+/-}\)\(\sim\)0.6), which differs from the theoretical value as explained previously, the increase in the size of the fibrils stops, the polymer is no longer integrated into the PA network and accumulates. The excess of polymer is undesirable because it induces unstructured areas formed from water-soluble polymers that may gradually dissolve and degrade the final material. To minimize these heterogeneity problems in the material, a R\({}_{+/-}\) equal to 1 was targeted for the rest of this work, leading to formation of fibrils with an approximate size of 60 nm. Strain sweep rheological experiments performed on 10 wt.% C\({}_{16}\)V\({}_{3}\)A\({}_{3}\)K\({}_{3}\)G-NH\({}_{2}\) aqueous solution (Figure 5A) at a constant frequency of 10 rad/s, showed that the mechanical properties deviated from the linear viscoelastic region above 0.5 % strain. Overall moduli are low when the PA is alone and the cross-over point from gel to liquid (G\({}^{\prime}\) = G\({}^{\prime\prime}\) occurred at about 3% strain. When the aqueous solutions of PA and polymer, prepared separately, are brought into contact, the medium becomes cloudy instantly (Figure 5B). A simple hand stirring makes it possible to homogenize the medium which forms a gel (Figure 5C). However, this gel is relatively weak and can break down irreversibly upon vortexing (Figure 5D). The presence of PSSNa increases the storage and the loss moduli by 4 order of magnitude and the cross-over point was pushed towards values of strain close to 100%. An oscillatory frequency sweep performed (Figure 6B) at a constant strain of 0.1% shows an almost independent frequency behavior over the explored range. It should be noted that for an R\({}_{+/-}\) of 0.6, the curve presents an erratic shape which is the result of a macroscopic separation observed under shear. The flow curve presented in Figure 6A demonstrates a marked shear thinning behavior. The elaboration of a membrane material from C\({}_{16}\)V\({}_{3}\)A\({}_{3}\)K\({}_{3}\)G-NH\({}_{2}\)-PSSNa mixtures requires casting a solution that has a sufficient viscosity to control the final material thickness and thus avoid the presence of imperfection linked to a film that is too thin. Consequently, a premixing of C\({}_{16}\)V\({}_{3}\)A\({}_{3}\)K\({}_{3}\)G-NH\({}_{2}\) and PSSNa solutions followed by casting on a support will not make it possible to obtain the expected morphology due to the too low viscosity of the solution under shear. One strategy  
Figure 4: (**A–C**) AFM of PA-PSSNa mixtures at different ratios of PA (+) charges/polymer (\(-\)) charges (R\({}_{+/-}\)). (**D–F**) Digital photographs of the PA-polymer gels. (**A,D**): R\({}_{+/-}=1/3\). (**B,E**): R\({}_{+/-}=1\). (**C,F**): R\({}_{+/-}=3\). (**G**) Average fibril diameter, estimated by AFM, as a function of the PA (+) charges /polymer (\(-\)) charge ratios (R\({}_{+/-}\)), standard deviation. then consists of depositing the two aqueous solutions successively and allowing the gel to form directly under its final geometry without subsequent manipulation. In order to estimate the time required for the formation of a sufficiently solid gel before immersing the obtained membrane in a water bath to wash out the unreacted precursors, the loss and storage moduli were followed over time at different concentrations going from 0.1 wt% to 10 wt% (Figure 7). Moduli values logically increase with the total solid concentration.