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Nanofibers composed of silica nanoparticles, used as structural building blocks, and polystyrene nanoparticles introduced as sacrificial material are fabricated by bicolloidal electrospinning. During fiber calcination, sacrificial particles are combusted leaving voids with controlled average sizes. The mechanical properties of the sintered silica fibers with voids are investigated by suspending the nanofiber over a gap and performing three-point bending experiments with atomic force microscopy. We investigate three different cases: fibers without voids and with 60 or 260 nm voids. For each case, we study how the introduction of the voids can be used to control the mechanical stiffness and fracture properties of the fibers. Fibers with no voids break in their majority at a single fracture point (70% of cases), segmenting the fiber into two pieces, while the remaining cases (30%) fracture at multiple points, leaving a gap in the suspended fiber. On the other hand, fibers with 60 nm voids fracture in only 25% of the cases at a single point, breaking predominantly at multiple points (75%). Finally, fibers with 260 nm voids fracture roughly in equal proportions leaving two and multiple pieces (46% vs 54%, respectively). The present study is a prerequisite for processes involving the controlled sectioning of nanofibers to yield anisometric particles.

The shape and size distribution of polystyrene (PS) compartments formed during emulsion electrospinning in a poly(vinyl alcohol) fiber is investigated. Stimulated emission depletion microscopy is employed to image the compartments with subdiffraction (super) resolution. The size distribution of the emulsion droplets in the spinning solution emulsions is found to be the key factor for fiber and compartment morphology. By varying the emulsification method, it is demonstrated that fibers spun from miniemulsions are characterized by a homogeneous distribution of PS compartments with no indication for coalescence or breakup of PS droplets. Coarse emulsions are prone to develop fiber instabilities associated with large PS domains. The domains are irregularly distributed in the fiber. Above a critical size of domains, breakup of these domains in two daughter domains is observed. The size dependence of the emulsion droplet breakup is explained by fluid dynamics.