Pvdf pellets

PVDF solution (20%) was prepared by dissolving 2 g PVDF pellets (M_W 275,000 g mol⁻¹, Sigma-Aldrich) in 10 ml solvent mixture of dimethylformamide (Sigma-Aldrich) and acetone (Sigma-Aldrich) (volume ratio of dimethylformamide and acetone, 4/6) and heated at 70 °C for 2 h. To examine the effect of fibre diameter on energy conversion, PVDF nanofibres with different diameters were prepared from PVDF solutions with the concentration ranging from 16 to 28%. The homogeneous PVDF solution was placed to a plastic syringe with a metal needle (21 gauge). A syringe pump (KD Scientific) was used to control the flow rate at 1 ml h⁻¹ and 15 kV high voltage was applied to the syringe needle using a high-voltage power supply (Gamma High Voltage). A grounded rotating drum collector (100 r.p.m.) placed 15 cm away from the needle tip was used for collecting the PVDF nanofibres.

PVDF pellets (M_w = 275 000 g mol⁻¹) were procured from Sigma-Aldrich (Tokyo, Japan). Based on a previous study,⁸ in which water also affected the crystal structure of PVDF, super dehydrated DMF (Fujifilm Wako Pure Chemical Corporation, Osaka, Japan) was utilized as the solvent for the spinning solution of PVDF. The ILs used in this study are summarized in Fig. 1. All the ILs were purchased from Tokyo Chemical Industries.

PVDF pellets with an average molecular weight of ~180,000 g/mol (M_w) and 71,000 g/mol (M_n) were purchased from Sigma Aldrich (St. Louis, MO, USA). Wood pulp CNF slurry (~4 wt % solids in water) was obtained from the University of Maine Process Development Center (Orono, ME, USA) and stored in a refrigerator at 4 °C until use. DMF (anhydrous grade, 99.8%) was purchased from Sigma Aldrich (St. Louis, MO, USA) and used immediately after opening. Through six cycles of DMF addition, centrifugation, and decantation, the aqueous CNF slurry was solvent exchanged in DMF, prior to incorporation into the PVDF/DMF solution. TOCNFs were prepared by mixing 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO, 0.06 g) sodium bromide solids (NaBr, 0.3 g) and bleach (6 wt % NaClO, 37.22 g,) to the CNF slurry (3 g) under vigorous stirring. After one hour, 10 mL of 0.5 M NaOH solution were added, followed by another 10 mL of the 0.5 M NaOH solution at two hours. After five hours, 15 mL of ethanol were added to quench the reaction. The TOCNFs were centrifuged and rinsed with deionized water (18.2 MΩ) three times before exchanging the water with DMF. The TOCNF slurry had a milky white color similar to the color of the as-received CNFs.