## 4 Results and Discussion
### Comparison of Pore-Size Distributions (PSDs)  
The FCP and LEP techniques provide flow-based and drained mass-based diameters, respectively, and both are based on the same Young-Laplace equation to estimate the PSD. Obviously, the experimental behavior of each technique and, consequently, the resulting PSD could be slightly different, depending on the interaction of the displacement or even extrusion liquid with each sample material, but also depending on the actual microstructure or pore connectivity of the membrane, which varies from one type to another. The aim of this study was to compare such results directly in the possible range (MF to particle filtration). For each membrane and technique, two repeated runs were carried out and the results were averaged. Figure 6a,b displays the PSDs and porometry run curves for the Anopore and PET membranes obtained via the LLDP technique, respectively. The pore diameters measured were in the range of 15-50 nm and the average pore diameter \(d_{avg}\) was \(22.6\pm 2.6\%\) nm for Anopore, while for the case of the PET sample, the pore diameters measured were in a narrower range of 17-40 nm with a distinctive peak pore diameter of 31 nm and a permeability-based \(d_{avg}\) of \(27.4\pm 2.1\%\). Remember that \(d_{avg}\) can be considered as a reliable estimation of mean pore size that allows for the size of particles typically retained by the filter to be estimated. Then, key observations for these two samples are that: (i) the repeated PSDs were similar for each sample, indicating good reproducibility and thereby reliability; and (ii) the \(d_{avg}\) values given by the LLDP method and nominal pore size were in good agreement (when nominal sizes were available). Figure 7a shows the PSDs of the CN Sartorius (5 \(\upmu\)m) membrane as obtained from GLDP. The \(d_{avg}\) value was 3.11 \(\upmu\)m with good reproducibility (error \(<\) 1%). In the case of the FM filter (Figure 7b), GLDP gave an average for pore diameter of 16.8 \(\upmu\)m; in this case, showing a sensibly higher discrepancy between both runs (\(\pm\)7.0%), which is also clear from both runs in Figure 7.  
Finally, the results from the LEP technique for both membranes are shown in Figure 8 where the LEP technique gave a higher variability than GLDP. Therefore, for the case of the CN membrane, the \(d_{avg}\) value was \(5.2\pm 5.7\%\)\(\upmu\)m, showing good reproducibility but clearly lower than that of GLDP and a slightly higher value when compared with GLDP. Notably, in contrast to the previous sample, the discrepancy between the GLDP and LEP results was clearly significant in the face mask. The results obtained for LEP also presented some variability with a mean value of \(d_{avg}=33.5\pm 7.1\%\)\(\upmu\)m. This sample to sample variability, which was higher for FM than for any other membrane studied (as can be seen in Table 2) can be attributed to the different fabrication method and the not-so strict control of the fabrication parameters. However, surely more important is that the different behavior of the FM filter (higher sample to sample variability) when compared with the CN membrane is clearly related with the inner microstructure of the FM fibrous medium, which can hardly be described as a simple bundle of parallel cylindrical pores [8; 9]. Particularly high is the discrepancy found when comparing the mean pore sizes for this FM filter from both techniques, resulting in a difference as large as 33.5 compared to 16.8 \(\upmu\)m. These differences can be related with a much broader PSD from 10 to 80 \(\upmu\)m, as approximately obtained for the LEP technique, which could be explained due a small contribution of extruded mass but enough to be registered at lower pressures where GLDP did not take account of any flow at this low pressure. Finally, Table 2 summarizes the mean pore size values found for each membrane analyzed along with the experimental errors.