S 5500

Scanning Tunneling Electron Microscopy (STEM) model S5500 (Hitachi High-Tech, Schaumburg, IL) was used to examine the morphology of the pure PVDF electrospun fibers and the five groups of PPy-coated PVDF fibers after polymerization for the various preselected time intervals. All specimens were coated with silver-palladium and imaged under 30 kV applied voltage at 3,000x and 15,000x magnifications. The collected micrographs were then analyzed to quantify orientation distribution of electrospun PVDF fibers, before and after PPy coating, using ImageJ (v1.8.0, NIH Image, Bethesda, MD) to evaluate the impact of PPy polymerization on the alignment of the PVDF fibers.

Phase analysis of the target and the nanoparticles was performed using an X-ray diffractometer (XRD, Philips, X’Pert-PRO-MRD, Netherlands) with a Cu-kα₁⁄kα₂ ratio of 0.514 radiation at 55 kV and 22 mA. All patterns were recorded over the angular range 10 ≤ 2θ/deg ≤90 with a step size of 2θ = 0.06 deg. The particle size and morphology were observed using scanning electron microscopy (SEM, Hitachi High-technologies, S-5500, Japan). Transmission electron microscopy (TEM, JEOL, JEM-2010F, Japan) was used to characterize the lattice fringe at high resolution with an acceleration voltage of 200 kV. The optical properties of the colloidal nanoparticles were analyzed by photoluminescence spectrophotometry (PL, Hitachi High-technologies, F-7000, Japan) with a 150 V Xe lamp and UV-vis (Jasco Corporation, V-670, Japan) at room temperature. Elemental analysis of the point-mode was performed by energy-dispersive X-ray spectroscopy (EDS, EDAX, Genesis APEX2 system, U.S.A.) combined with TEM, while area-mode analysis was produced by EDS (Horiba, ENERGY EX-250, Japan). Except for X-ray diffraction analysis, the colloidal nanoparticles used for all characterization throughout the study were filtered with a 0.22 μm pore-size filter.

The conductivities of the prepared aqueous solutions were measured using a conductivity meter (HORIBA Co. Ltd., LAQUA (F-74) with conductivity measurement cell (3,552-10D)) at 25 °C.
The surface tension was estimated using the standard pendant drop method, wherein a droplet (15 μL) formed using a 20 G needle was photographed for 10 s after the formation of the droplet using a contact angle analyzer (B100W, Asumi-giken) followed by analysis of the image using the Young–Laplace equation ^{28 (link)}. The measurement was repeated five times. Before the measurement, the syringe and needle were washed thoroughly using isopropyl alcohol followed by repetitive filling and expelling of the sample solution from the needle (Supplementary Fig. 8).
The viscosity or rheological behavior of the PVP solutions was evaluated using a rotating rheometer (TA Instruments, ARES G2). The viscosities of the solutions were measured at shear rates between 10⁻¹ and 10³ s⁻¹. The electrospun samples were characterized by SEM (HITACHI High-Technologies, S3600N and S-5500). Au was deposited less than 4 nm estimated by quartz thickness monitor on the prepared electrospun samples with a desktop magnetron sputtering system (HITACHI High-Technologies, MC1000) to obtain clear SEM images. A total of ~ 100 fibers were randomly selected from the SEM images for calculating the average diameter and standard deviation.

The morphologies of the PSt microspheres before and after PANI coating were observed using a field emission scanning electron microscope (FE-SEM) (S-5500, Hitachi High-Technologies). The X-ray diffraction (XRD) analysis was carried out on an X’pert Pro (PANalytical) with Cu Ka radiation.