*3.3. Fiber Morphology*

It is well known that polyaniline obtained by aniline polymerization can occur in three oxidation states [21]:


Of all forms of polyaniline, only emeraldine salt (green) has an electrical conductivity at the level of semiconductors, i.e., around 1 S/cm. Emeraldine salt is obtained as a result of emeraldine base modification by HCl or HBr. Each type of polyaniline can be transformed in a reversible process of oxidation or reduction, during which changes in color and electrical conductivity occur [22].

The PAN/PANI blended fibers obtained by adding polyaniline powder to the spinning solution had a dark green color (Figure 3a), which, after immersing them in a 3% aqueous solution of hydrochloric acid, turned to dark blue (Figure 3b). After rinsing again in water, their color returned to the previous color. The fibers obtained as a result of the synthesis of polyaniline in situ in the spinning solution were dark navy (Figure 3c).

(**b**)

**Figure 3.** Fiber images made with an optical microscope. Fibers obtained as a result of the addition of polyaniline (PANI): (**a**) after rinsing in water; (**b**) after rinsing in HCl; and (**c**) fibers obtained as a result of in situ synthesis of PANI.

Based on the color of the obtained fibers, it can be concluded that polyaniline in the PAN/PANI blended fibers was in an emeraldine base form, and in an HCl solution it transformed into emeraldine salt (Figure 3b). Moreover, in the PAN/PANI in situ fibers, polyaniline was in the emeraldine base form.

(Per)nigraniline—(C6H4N)n—a completely oxidized form of PANI—also has a blue or violet color. However, taking into account that the synthesis of polyaniline was carried out in a solvent (DMF), which is a strong reducer, it cannot be assumed that a fully oxidized form of PANI was formed. In addition, during the synthesis of PANI in DMF, colorless crystals were formed, which indicated that a part of polyaniline precipitated in the form of leucoemeraldine—a completely reduced form. A significant part of the leucoemeraldine was filtered during the synthesis, and, therefore, the fibers were mostly polyaniline fractions with shorter chains.
