Fig. 3.

SEM images of electret (a) PS/PVDF-1, (b) PS/PVDF-2, and (c) PS/PVDF-3 fibers. Inset of (b) is the distribution of atom F. (d) Surface potentials of PS/PVDF electret fibers. (e) Schematic illustrating the contribution of PVDF on electret effect. (f) A color map showing the electric field around single PS/PVDF-2 fiber. (g) Filtration performance of various electret PS/PVDF materials. (h) Comparison of filtration performances [17], [20], [32]. (i) A N95 respirator using PS/PVDF-2 fibers as the core material. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)