A Nonsolvent-Assisted Electrospinning Strategy for High-Toughness Polyimide Fiber Membranes from Low-Concentration Precursors

Sufficient chain entanglements are essential for high-quality fiber membranes via electrospinning. This often requires high polymer concentrations, which result in excessively viscous solutions, hindering processability. Herein, we report a nonsolvent-assisted strategy to enhance chain entanglement and enable electrospinning to form bead-free fiber membranes at low concentrations of poly(amic acid) (PAA), the precursor of polyimide (PI). By incorporating nonsolvents into PAA solutions, binary solvent systems were constructed, which induce polymer chain contraction and strengthen intermolecular interactions, thereby facilitating entanglement networks. Thus, bead-free fiber membranes can be obtained at lower concentrations in an expanded electrospinning window of the PAA solutions. The minimum concentration required for bead-free fibers decreased from 16 wt % in pure DMF to 10 wt % in a binary solvent containing 43% nonsolvent. Increasing the proportion of nonsolvent also leads to an increase in average fiber diameters. The resulting PI fiber membranes exhibited substantially improved mechanical properties, especially in terms of toughness. Furthermore, the PI fiber membranes demonstrated an excellent oil–water separation performance. This work provides an efficient and scalable solvent-based strategy for facilitating the electrospinning of high-performance polymeric membranes with tailored properties.