Abstract
The electrospinning of high-performance polyimides (PI) has recently sparked great interest. In this study, we explore the effect of the electrospinning parameters — namely polymer concentration, voltage, tip-to-collector distance and flow rate — and salt addition on the diameter, morphology, and spinnability of electrospun PI nanofibers. Three different polyimides of intrinsic microporosity (PIM-PIs) with high Brunauer–Emmett–Teller (BET) ranging from 270 to 506 m2 g−1, and two microporous polyimides, were synthesized through the polycondensation of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and aromatic diamines. The addition of tetraethylammonium bromide (TEAB) salt considerably increased the conductivity of all the PI solutions, significantly improved spinability, and resulted in thinner fibers. We also used molecular dynamic simulations to investigate the macromolecular mechanism of improved spinnability and fiber morphology in the presence of an ammonium salt. The small droplets detached from the parent droplet, followed by the rapid evaporation of the ions through the hydration effect, which facilitated the electrospinning. The resulting uniform nanofibers have great potential in environmental applications due to the presence of microporosity and hydrophobic pendant trifluoromethyl groups, which enhance the sorption performance of the fibers for hydrophobic species.
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•Five different microporous polyimides having pendant trifluoromethyl groups were synthesized through polycondensation.•Uniform nanofibers were produced at low polymer concentrations due to improved spinnability in the presence of a salt.•Higher salt content drastically increased the solution conductivity and led to thinner electrospun fibers.•A higher flow rate increased fiber diameter due to the higher mass flow.•Molecular dynamics simulations demonstrated faster solvent evaporation in the presence of salt.