*2.5. Characterization*

The molecular weights of polymers were determined by gel permeation chromatography (GPS) using dimethylacetamide (DMAc) as a solvent with the addition of 0.5 wt.% lithium chloride (LiCl). Rheological measurements of the spinning solutions were obtained by a ReolabQC Anton Paar rheoviscometer (Anton Paar, Ostfildern, Germany). The kinetics of polyaniline formation in the DMF were investigated using UV-Vis spectroscopy with a UV-Vis-NIR JASCO V-570PC spectrophotometer (Jasco, Easton, MD, USA). Photographs of the fibers were made using a Leica DM 4000M Led microscope (Leica, Wetzlar, Niemcy). The chemical composition was determined on the basis of infrared spectroscopy with a Nicolet 380 FTIR spectrophotometer (Thermo Fisher Scientific, Waltham, MA, USA) with an ATR Smart Performer (Thermo Fisher Scientific, Waltham, MA, USA). A PC-controlled low-load machine was used for testing the mechanical properties of the fibers formed (Zwick Z2.5/TN1S, Ulm, Germany), according to the PN-EN ISO 2062:2010 standard [18]. The fiber samples' morphology was analyzed with a TESCAN VEGA3–EasyProbe (TESCAN, Brno, Czech Republic), and a scanning electron microscope (TESCAN, Brno, Czech Republic) equipped with VEGA TG software (TESCAN, Brno, Czech Republic) was used for morphological analysis of the doped polyacrylonitrile fibers (high vacuum mode (SE); accelerating voltage 7–20 kV). Before the measurements, the samples were sputtered with Au-Pd (SC7620 Mini, Quorum Technologies Ltd., Lewes, UK) for 120 s. The cross-section of the fibers was observed and obtained using a high-resolution SEM Xe-PFIB FEI Helios (Brucker, Billerica, MA, USA). A single fiber was covered with a platinum layer, and then a cross-section was made with a focus ion beam (FIB). Thermal gravimetric analysis (TGA) was carried out using a thermobalance TGA Mettler Toledo (Columbus, OH, USA) in the temperature range from 25 to 600 ◦C and a heating speed of 10 ◦C/min. A corundum crucible with a hole in its lid of 70 μL was used. Measurements were carried out under nitrogen, and the flow rate was 30 mL/min. Differential scanning calorimetry (DSC) measurements were performed using a DSC Mettler Toledo (Columbus, OH, USA) in the temperature range from 25 to 200 ◦C with a heating/cooling rate of 10 ◦C/min. Measurements were carried out under nitrogen, and the flow rate was 30 mL/min in a corundum crucible with one hole in its lid of 40 μL. The study of electrical conductance was investigated using the direct current (DC) method with the use of a Keithley 2000 multimeter (Cleveland, OH, USA). Measurements were made on 1 cm lengths between two silver electrodes.
