*2.6. SCMs Characterization*

#### 2.6.1. Mechanical Tests

The elastic moduli G' (filled symbols) and the viscous moduli G (open symbols) of the F1 and F3 SCMs and nc-SCMs are reported in Figure 5. G indicates the capability of the material to store energy and G refers to the capability of the material to dissipate energy. All of the samples that were examined showed relatively high moduli (in the range of 104–105 MPa for the elastic modulus).

**Figure 5.** The elastic moduli G (filled symbols) and the viscous moduli G (open symbols) of the SCMs (SCM-F1, triangles; SCM-F3, stars) and not crosslinked SCMs (nc-SCM-F1, circles; nc-SCM-F3, diamonds) reported in function of the frequency applied by the rheometer in the dynamic mechanical analysis (for methods see Section 4.5.3).

As expected, for a gel system, a solid-like behaviour was observable. Indeed, it was possible to note the predominance of G upon G at low frequencies in all of the membranes, while G increased on increasing the frequency till reaching a crossover between the moduli. These data indicate that all of the tested samples show an evident elastic behaviour in the frequency range that was studied.

Both SCM-F1 (triangles) and nc-SCM-F1 (circles) showed lower moduli than SCM-F3 (stars) and nc-SCM-F3 (diamonds), indicating, in general, a lower mechanical stiffness. Moreover, as is clearly observable, the crosslinking did not affect the mechanical performance of F1-derived SCMs, with the two samples (nc-SCM-F1 and SCM-F1) showing comparable values of both G and G. On the contrary, in F3-derived SCMs, a significant difference was observable between the nc-SCM-F3 and the SCM-F3, with an evident increase of the mechanical properties in the crosslinked sample, as evidenced by a higher G elastic modulus when compared to the nc-SCM-F3.
