Effect of the Fiber Diameter of Polyamide 11 Nanofibers on Their Internal Molecular Orientation and Properties

Herein, the effect of the diameter of polyamide 11 nanofibers (PA11 NFs) on their internal structures as well as thermal and mechanical properties is investigated. Aligned PA11 NFs with diameters ranging from 109 to 462 nm are prepared by the single-component solvent electrospinning of different PA11/1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) solutions (4-8 wt%) and subsequently characterized. Owing to the similar hydrogen bond formation within the NFs during electrospinning, all prepared NFs have δ'-phase crystals with similar crystallinities and crystallite sizes. However, the orientation of the δ'-phase crystals is disrupted in NFs with diameters less than 200 nm, due to the rapid solidification during electrospinning. The δ'-phase crystals are the most highly oriented within NFs having a fiber diameter of ≈300 nm, and the corresponding NF sheets exhibit the highest mechanical strength. A single PA11 NF with a fiber diameter of ≈300 nm also exhibits a good piezoelectric response (piezoelectric coefficient d33 = 2.1 pm V-1 ).