Polyaniline Nano Films Synthesis in One Step via Chemical Oxidative Polymerization

Polyaniline films were successfully synthesized in this study using an oxidative polymerization method at temperatures ranging from 0 to 4 ° C. Polyaniline films were deposited using a single step of chemical oxidative polymerization rather than electrochemical polymerization. The polyaniline was examined using FTIR, XRD, SEM, AFM, and Four Point Probe. This result demonstrates that polyaniline synthesized using this method has a uniform morphology, small size (17 to 40) nm, high crystallinity, and high conductivity (9.42 s/cm).


Introduction
Polyaniline (PANI) a semi-flexible conducting polymer of the organic semiconductor family, as a result of its extraordinary qualities, such as good conductivity, environmental stability, an interesting redox process, low cost starting material, and more 1 . PANI, a conjugated polymer, has been used in a variety of applications across a variety of disciplines, including biosensors 2 , supercapacitors 3 , actuators 4 , electromagnetic interference shielding 5 , membranes 6 , biofuel cells 7 , light-emitting diodes 8 , corrosion protection 9 , photovoltaic cells 10 , solar-cell devices 11 , rechargeable batteries 12 , field-effect transistors 13 , and more.
There are numerous types of polyanilines, each with unique physical and chemical characteristics Fig.1 14 . They can be categorized as emeraldine, leucoemeraldine, and pernigraniline depending on their oxidation state. For example, pernigraniline is discovered in a fully oxidized state while leucoemeraldine is found in a suitably reduced condition 15 . Because nitrogen atoms are involved in the creation of radical cations, unlike most electro conducting polymers whose radical cation is created at carbon, polyaniline conductivity differs from that of other electro conducting polymers. On the other hand, the conjugated double bond system also involves nitrogen. In light of this, polyaniline's electrical conductivity depends on both its oxidation and protonation levels [16][17][18] . Polyanilines are distinguished by their ability to take on several oxidation forms. To conduct the form of emerald salt, polyaniline in the form of emeraldine base can be doped (protonated). Half-oxidized forms of emeraldine bases include an equal amount of amine (-NH-) and imine (=NH-) sites 19 .
In chemical oxidative polymerization (COP), PANI is synthesized using hydrochloric acid (HCl) or sulfuric acid (H2SO4) as a dopant and ammonium persulfate (APS) as an oxidant in an aqueous medium 20 . At this time, a proton can be removed by the oxidant from the monomer of aniline without either creating a heavy bond, or with the absolute product 21 .
The recommended procedure in this case is the oxidation of monomers to make a cation radical, followed by coupling to create a di-cation and repeating to create a polymer, which is an oxidative coupling 22 .
The unique properties of nanoparticles are introduced by a conductive polymer. PANI is related to various properties, including magnetic 23 , electrical and dielectric 24 , redox 25 , anti-corrosion 26 , charge-discharge 27 , capacitive 28 , and sensor properties 29 .
The novelty of this research is deposition thin films of polyaniline by one step chemical oxidative polymerization without using electrochemical polymerization.

Materials and Methods
Aniline (99%) was purchased from Merck (Germany), ammonium persulfate (APS) was provided by Aldrich Company. The synthesized polyaniline was characterized by FT-IR spectroscopy/ PerkinElmer, to characterize functional group. X-ray diffraction patterns of the coatings were obtained by employing Philips /X'PERT PRO using CuKα (Kα =1.54056 Å) radiation. Morphological characterization by Field emission scanning electron microscopy (FESEM) and Atomic Force Microscopy (AFM)/ TT-2 AFM Workshop. The electrical conductivity studies were performed using four probe method.

Synthesis of polyaniline
PANI was synthesized by chemical oxidative polymerization of aniline in acidic medium. In a typical procedure, to a 250-mL flask and ITO glass, 100 mL of hydrochloric acid (0.1 M) and 2 mL of Ani (0.021 mol) were added, and the mixture was stirred and cooled down to 0-4 º C. Then, 0.5 M APS solution (100 mL) was added dropwise within 30 min. The reaction mixture was further stirred for 5 hours at 0-4 ºC to complete the polymerization as shown in Fig. 2. On completion of reaction, the resulting dark green precipitate was filtered and washed several times with ethanol and deionized water 30 , the PANI films was washed also with deionized water. Finally, the resulting PANI was dried over night at 60 ºC under vacuum.

Conductivity Properties
Conductivity of polyaniline thin film was measured at room temperature by a four-probe method, which used for measuring sheet resistance and conductivity, represented in Table 1.

Chemical and Molecular Studies
To study the PANI reaction during chemical oxidation, FTIR spectroscopy was used. Fig. 3 displays the PANI FTIR spectra in the 480-4000 cm -1 region. The 1,4-disubstituted benzene ring's out-ofplane vibration, also known as the para-coupling structure, is responsible for the 801 cm -1 and 507 cm -1 peaks. The monosubstituted aromatic ring is the source of the peak at 688 cm -1 .
Pure PANI's spectra displayed the typical distinctive stretching vibration bands at 1490 cm -1 (C=C, benzenoid rings), and 1562 cm -1 (C=C, quinoid rings), 1043, 1076 and 1095 cm -1 (C-H) 31 , 1126 cm -1 (quinone ring stretching vibration), 1200 cm -1 (C-N in plane), and 1383 cm -1 (aromatic C-N stretch). Due to the existence of (C=N stretching in aromatic), the characteristic peaks at 1460 cm -1 and 1557 cm -1 are caused by (aromatic C-C stretching). The N-H bend is associated with the 1615 cm -1 and 1650 cm -1 peak. The peaks at 2326 and 2358 cm -1 corresponds to C-N triple band. The peaks at 2875 and 2920 cm -1 corresponds to C-H stretching 32 . XRD analysis of the PANI thin film's crystal structure was performed, and the results are shown in Fig. 4. According to JCPDS card no. 53-1891, the diffraction peaks found at 2θ = 22.13 degrees and 25.53 degrees, respectively, in this picture demonstrate the amorphous character of PANI (poor crystallinity), and they correspond to 011 and 200 according to the previous studied, respectively 33 .
Using the Debye-Scherrer equation, the PANI's grain size is calculated in Eq.1 and the structural parameter of PANI was presented in Table 2.
Where the Scherrer constant, λ is the light's wavelength utilized for diffraction, β is the sharp peak's complete width at half maximum and θ is the angle being measured". In the calculation above, the Scherrer constant ( ), which takes into account the particle's shape, is typically assumed to be 0.9 34 .

Morphology and Roughness Analysis
FESEM analysis of the surface morphologies of the deposited PANI thin films is depicted in Fig. 5. A and B. The homogeneous deposition of the polymer over the substrate was visible in the FESEM image of the PANI thin films. According to Fig. 5A, these nanotubes have a diameter of 17 to 40 nm and a length of a few micrometers. The surface morphology and roughness of the PANI thin film asdeposited were also examined and measured using AFM. The AFM pictures of the PANI thin films, which demonstrate the deposition of grain-like tubes to generate a thin film, are shown in Fig. 5 C. These results are in line with the SEM pictures, which also showed comparable morphologies. The PANI films' surface roughness was determined to be 7.715 nm as shown in Table 3. When the substrate was already present in the reaction before the addition of an initiator, such as APS solution, uniform film deposition could be observed. The thickness of the films was significantly reduced if the substrate was added during the induction period, which is between one and three minutes after the polymerization began. Similar to this, if the substrate was added after 6-7 min, no films were formed because aniline cation radicals, which are necessary for primary nucleation, were not present. In order to generate high-quality and stable films with a corresponding surface roughness of 7.715 nm, the substrate has to be added before polymerization.

Conclusion
We conclude from this research that the concentration of the acid and the temperature at 0-4 ° C for about 6 hours and amount of oxidant lead to formation nanotube of polyaniline and deposit it directly on the ITO glass substrate with the dimeter of 17 to 40 nm and roughness of 7.715 nm.

Acknowledgment
The cooperation of the University of Anbar is appreciated -Authors sign on ethical consideration's approval.

Authors' Declaration
-Ethical Clearance: The project was approved by the local ethical committee in University of Anbar.