Chemical and structural induced ductile-to-brittle transition in electrospun silica nanofiber membranes

Electrospun silica nanofiber membranes show a high potential in many advanced environmental applications. However, little is known about their mechanical performance which could be a limiting factor for further innovation. It is shown in this work that silica nanofiber membranes have a completely different deformation behavior compared to conventional polymeric/thermoplastic nanofiber membranes, resulting from their significant differences in chemical and physical properties such as fiber interactions and porosity. Furthermore, storage at room temperature initiates remarkable changes in failure mechanisms, depending on the storage humidity, which can be accelerated via a thermal treatment. These changes are linked to the structural changes of the membrane resulting from its chemical reactivity towards moisture in the air. Additional interactions and crosslinks are observed, leading to fiber shrinkage and rearrangement. As a result, more contact points are created between nanofibers, creating additional friction forces and, as such, a complete shift in mechanical properties towards a stronger, stiffer, and more brittle material (tensile strength of 14.0 ± 3.8 MPa vs. 3.1 ± 0.4 MPa and failure strain of 0.9 ± 0.2% vs. 24.2 ± 1.0%). The silica nanofiber membranes thus allow mechanical tunability via altering the storage or treatment conditions.