Preliminary Investigation of the Influence of Potentiodynamic Electrosynthesis of Polyaniline@Carbon Fiber on the Formation of Charge Carriers and Their Effects on Double Layer
Authors: Galvao Aline Guedes , Poli Anne Karoline dos Santos , Gama Adriana Medeiros , Gonçalves Joseane Mercia da Rocha Pimentel , Gonçalves Emerson Sarmento 
Published: February 2020

Aerospace systems contain a number of electronic devices responsible for data acquisition and transmission, device control, and power storage. Resistant structural materials, and light electronics are of strong interest to the aerospace industry. Thus, it is possible to aggregate these properties in a single electroactive composite material for application in new aeronautical structures of panels, circuits, de-icing and anti-icing systems, and sensor integration. The combination of carbon fiber with conductive polymer results in a material that can replace printed circuit board metal with improvements in the properties of thermal and mechanical resistance, and density resulting in a lighter material and electric conductor. The most suitable forms of electrodeposited polyaniline in carbon fiber structural cables were tested, through analysis of number of electrochemical cycles influence. In general, the electrochemical cell can be described as carbon fiber (CF) used as work electrode, against platinum electrode, using cyclic voltammetry in the region of -0.50 V to +1.05 V vs. Ag/AgCl at variable sweep rate from 5 mV/s, and different numbers of voltammetric cycles, 2, 4, 6 and 9, in a 0.5 mol/L aniline and H2SO4 0.5 mol/L solution The cyclic voltammetry shown in Figure 1 shows the anode peak of interest around 0.25 V, which is the potential for maximum formation of emeraldine in the fiber, used as the final potential of each process of obtaining..

Morphological (Scanning Electron Microscopy), structural (X-ray Diffraction) and chemical (Infrared Spectroscopy by Fourier Transform) analyzes were performed. It is possible to observe that the morphology advances for more intense deposition of polyaniline on carbon fibers. Noticeable forms: “coral reef”, alveoli, nanofibers. The diffractograms have polyaniline@Carbon fiber peaks, showing that polyaniline (001) is oriented by the carbon fiber (002) for the first cycles, close to 10°. In addition, polyaniline grown to cycle 2 exhibits a relatively small population of structures growing in the directions associated with 2Θ = 12°, 17°, and 34°, most common in the case of chemical synthesis. In the diffractogram of polyaniline grown up to cycle 4, there is a significant contribution obtained in 6,2° competing with the growth of orthorhombic structures around 9°, as it had been presented in 2 cycles. For the polymer obtained after 6 and 9 cycles, the peaks 17° and 25° show higher incidence. These new orientations indicate that growth does not occur on both the fiber surface and on the previously formed polyaniline itself.

The identification of functional groups was useful for confirming the formation of emeraldine and its conductive, saline, more or less protonated form. However, all samples present bands related to the C=C stretch in the structure of the quinoid and benzenoid ring, proving the presence of polyaniline. The proximity of the height of these bands, between 1565 and 1490 cm-1, indicates the obtaining of the emeraldine form, which is the most susceptible to electric charge accommodation. However, there are no bands expressing between 1240-1255 cm-1 relative to the assignment of the C-N stretch in the BBB sequence (which does not favor electroactivity), indicating that there are no long sequences of benzenoid groups in the polymer, which does not have definitively insulating chain branches , since the BBB sequence is insulating.

According to the literature, the degree of oxidation of PAni is calculated by Equation 1, the ratio of the presence of quinoids. Equation 2 shows how to calculate the S ratio of protonated C-N groups. The higher the value of S, the greater the number of protons accommodated, and therefore, the greater the electroactivity. Through Bode Plot, it is possible to calculate the relaxation time (t) of each sample. Table 1 presents the values of y, S and t, as they enabled quantification of the spectra of Figures 3, 4 and 5. Being y ~ 0.5 (emeraldine) for all samples, the electroactivity is favored, with slight variations in the degree of protonation . However, for 6 cycles, only 76% of the species are protonated. In this case, the electrochemical relaxation time was higher, indicating that the shortage of accommodated load allows for greater storage, making it difficult to release them, being less suitable for the aforementioned circuits (Table 1). The Polyaniline@carbon fiber most suitable for this purpose should be closer to that obtained with 4 cycles.

Figure 1