Infrared Spectra : Useful Technique to Identify the Conductivity Level of Emeraldine form of Polyaniline and Indication of Conductivity Measurement either Two or Four Probe Technique

A new insight was watched the connection between’s the conductivity and Fourier Transform Infrared (FT-IR) spectra of the emeraldine type of polyaniline (PANI) structures. The conductivity of polyaniline emeraldine salt (PANI-ES) can be varied from 101 to 10-12 S cm-1. FT-IR spectrum is a tool to determine the conductivity level and also conductivity measuring methods of PANI system, i.e., either two probe or four probe techniques. This information is very useful for the researcher and industrialists working on emeraldine form of PANI systems to identify the conductivity level and method of measurements from FT-IR spectra. This data was seen from the infrared spectra of different PANI salts obtained by the oxidation of aniline in water/solvent medium by ammonium persulfate (APS) without utilizing any acids. PANI-ES samples having reasonably good conductivity (> 0.3 S cm-1) showed mostly nanowires or nanorods morphology, whereas, lower conductivity (<0.3 S cm-1) samples showed mostly agglomerated spheres or particles morphology. In these investigations, however, no report was made of the use of infrared technic to determine the conductivity of PANI system. Article History Received: 08 September 2018 Accepted: 15 November 2018


Introduction
Polyaniline is most studied conducting polymer throughout the world because of its easy synthesis, environmental stability, reasonably good electrical conductivity, tunable electrical properties via oxidation/reduction chemistry (unique acid/base doping/dedoping process), and inexpensive material.PANI exists in three different forms, i.e., leucoemeraldine (completely insulator), emeraldine (insulator to the semiconductor) and pernigraniline (conductive).Polyaniline can be synthesized by chemical oxidative synthesis, 1 electrochemical polymerization, 2 rapid mixing polymerization, 3 Emulsion Polymerization, 4 in situ seeding polymerization 5 or using templates and surfactants. 6Among these techniques, interfacial polymerization is a standout amongst the best methodologies, which creates amazing PANI nanostructures in extensive quantities. 7The conductivity of polyaniline emeraldine base (PANI-EB) increments reversibly with doping from the undoped base (10 -10 S cm -1 ) to the completely doped, emeraldine directing salt frame (10 1 S cm -1 ).The doping level can be tuned basically by controlling the pH of the dopant and this can be controlled either chemically or electrochemically by changing the oxidation state.The tunable electrical conductivity accomplished by doping/de-doping makes PANI is a promising material for some, applications incorporating into batteries, sensors, actuators, electromagnetic protecting, antistatic coatings, corrosion resistance, electro-optic, electrochromic gadgets, and division layers and so on.10] PANI is typically prepared in water medium at room temperature 11 or at low temperature. 12,13he response continues to the development of a green encourage.PANI can likewise be set up in the solid state when no dissolvable is used, 14,15 for the two strategies just granular morphology is typically framed.Then again, if polymerization continues at the interface of two immiscible fluids, PANI nanofibres are obtained. 16,17On the off chance that amid oxidation a surfactant or a water-solvent polymer is added to the reaction, PANI colloids are shaped.
It has been exhibited by Gospodinova et al 18 that the polymerization of aniline additionally continues well in water, with no additional acid, when ammonium peroxydisulfate was utilized as an oxidant.In our gathering likewise already revealed that the aniline was oxidized with APS at high temperature with no acid dopant. 19 the present work, PANI-ES were set up without utilizing any additional hazardous acid by the oxidation of aniline utilizing APS.PANI-ES was de-doped to PANI-EB utilizing aq.NaOH.In the present paper, aniline was oxidized with ammonium peroxydisulfate in water/organic solvent medium without any additional acid, and was evaluated by morphology, FT-IR and conductivity measurements.The conductivity of the sample >0.1 S cm -1 to be estimated by means of four probe technique, and the conductivity <10 -9 S cm -1 to be estimated utilizing high resistance meter.Conductivity in the range 10 -2 to 10 -9 S cm -1 can be estimated utilizing even a typical multimeter.Four probe procedures include the estimation of voltage by passing the current.Subsequently, it needs consistent current source and voltage estimation hardware with the required exactness, which are costlier gear for the business.This paper reports that FT-IR could be utilized to discover the conductivity level in emeraldine frameworks, and the strategy for estimation of the conductivity of the emeraldine samples through high resistance meter, two or four probe methods.
Polyaniline-sulfate salt (PANI-H 2 SO 4 ) 20 was prepared by traditional polymerization pathway by the oxidation of aniline within the sight of sulphuric acid utilizing ammonium persulfate oxidant (APS).

Materials
Aniline (AR grade) was obtained from S. D. Fine Chemicals, Mumbai, India was vacuum distilled prior to use.Ammonium persulfate and Sulphuric acid (H 2 SO 4 ) were obtained from Sigma Aldrich,Bengaluru, India.All the solvents (AR grade) were obtained from Rankem, Hyderabad, India.All the reactions were carried out with distilled water.Polyaniline-sulfuric acid (PANI-H 2 SO 4 ) salt and its corresponding base were prepared by following our earlier report. 20

Characterization
The details of characterization techniques are given in Table 1.

Experimental Procedure Synthesis of PANI-ES in organic solvents without using acid dopants
A progression of polyaniline emeraldine salts (PANI-ES) incorporated with the nonappearance of corrosive through interfacial polymerization 4 of aniline in water and natural dissolvable blend.In an ordinary test, 15 mL of solvent was taken in a 100 mL tapered flagon and included 1 mL of aniline.An oxidizing specialist APS (2.8 g) in 30 mL of water was added gradually through the side of the funnel shaped flagon amid a time of 15 to 20 min.The response blend was kept at 5 o C in an ice box without mixing for 24h.The green shaded powder was separated, comprehensively flushed with water refined lastly with 250 mL of (CH 3 ) 2 CO.The powder test dried at 60 o C till a steady weight.

Preparation of PANI-EB
De-doped the polyanilineemeraldine salt (PANI-ES) to polyaniline emeraldine base (PANI-EB) by blending 0.5 grams of PANI-ES in 50 mL of an aq.1 M NaOH for 4 h at enveloping temperature.The blend was isolated and washed with 50 mL of aq.1 M NaOH, 500 mL of deionized water, in conclusion, 50 mL of (CH 3 ) 2 CO.The powder was dried at 60 °C until to obtain a constant weight.

Results and Discussions
Morphologies of the PANI-ES prepared in the mixture of aqueous/organic solvents medium are shown in Fig. 1.The images showed mostly two types of morphologies, i.e. nanowires or nanorods and agglomerated spheres or particles.
FTIR spectra and conductivity measurements were carried out for the PANI-ES and their corresponding bases.The PANI-EB can, in principle, be described by the following general structure (Structure 1).shown in Fig. 2 and the major peaks observed are indicated in Fig. 2.
The FT-IR spectral results for the PANI-ES prepared using various solvents are detailed in Table 3.  2.
On protonation, PANI-EB changes to PANI-ES, wherein, nitrogen atom changes to protonated radical cation (NH +• ).This PANI-ES has the functional groups such as N-H,N- Thus in the case of PANI-ES, an extra peak should appear for N-H +• (3225 cm -1 ), and the peak due to C-C (1380 cm -1 ) disappear when compared with that of PANI-EB.Also, peak shifts are expected due to the aromatic nature of PANI-ES.These changes are also observed in the PANI-H 2 SO 4 salt (Table 2).In addition, based on the present result and experience of the authors,the range of the peaks for most of the PANI-salts and bases were identified.These values are also included in Table 2. FT-IR spectra of PANI-H 2 SO 4 salt and its base are  vs -Very small peak observed, s is small a peak appears as doublet peak toluene, benzene, hexane, dichloromethane, chloroform and the second set of solvents are water, methanol, ethanol, isopropanol, tetrahydrofuran.The peaks observed at lower wavenumber for the PANI-ES prepared using the first set of solvents compared to that of the PANI-ES prepared using the second set of solvents.In addition, a peak appears in the case of the second set of solvents at around 1040 cm -1 and this peak is due to C-O-C.The clear peak shifts are observed in C=C (quinonoid ring), C C (benzenoid ring),C-NH +• -C and N C -C 6 H 4 -N D H +• .di substituted benzene.The range of FT-IR peaks observed for reported PANI-salts, PANI-ES prepared using various solvents and its corresponding bases are listed in Table 5.
This Table 5 also indicates the correlation between FT-IR spectrums of PANI systems with its conductivity and method of measurement of conductivity of PANI systems.This information is a very useful researcher and industrialists working on PANI systems to find the conductivity level and method of measurements from FT-IR spectrum.Similarly, theconductivity of PANI-ES shows two sets of value (Fig. 4), i.e., >0.3 S cm -1 for the first set of solvents and <0.3 S cm -1 for the second set of solvents.Conductivity measurement by a two probe method by the following equation Where l is the thickness in cm, r is the radius in cm and R is the resistance of the pellet in Ω.
Morphology and conductivity are impor tant phenomenal in PANI systems.In this work,we notified morphologies and conductivity tuning with solvents.These results in signpost solvent choosing also important factor prepare of emeraldine PANI systems.

Conclusion
In conclusion, emeraldine form of PANI either in salt or base form could be found from the FT-IR spectrum without conductivity measurement.In this work, PANI-ES systems were prepared without acid in two sets of solvents.A correlation between FT-IR spectral peaks and conductivity level of emeraldine PANI system was established.Also, FT-IR spectral peaks could be used to indicates the type of method of conductivity measurement i.e., either two probe or four probe techniques.The peaks observed at lower wave number in FT-IR spectrum for the higher conductivity PANI-ES (>0.3 S cm -1 ) compared to the lower conductivity PANI-ES (<0.3 S cm -1 ).The scope of this work is to indicate that FT-IR spectrum could be used to find out the conductivity level of PANI-ES samples and its measurement technique, i.e. either using ordinary multimeter with two probes or four probes measurement.

Fig. 1 :Structure 1 :
Fig. 1: SEM images of PANI-ES prepared with 1 st set of solvents and 2 nd set of solvents.

.
These PANI-ES spectra showed peaks due to N-H, N-H +• , C=C, C C, C-N-C, C C-H, C-NH +• -C, Major peaks are analyzed by considering the above structure of PANI-ES and PANI-EB.PANI-EB has FT-IR functional groups such as N-H, C=C, C C, C-C, C-N-C, C C-H, C-N=C, 1,4-disubstituted benzene (N C -C 6 H 4 -N D ).Peaks due to these functional groups are obtained in the FT-IR spectrum of PANI-EB is shown in Table

A
clear correlation observed between the conductivity and FT-IR peak positions for emeraldine salt and its base.Reported emeraldinepolyanilinesalts having conductivity (2 to 5 S cm -1 ) showed peaks due to C=C, C C, C-NH +• -C and N C -C 6 H 4 -N D H +• .atlower wavenumbers compared to its corresponding base, which is having very low conductivity (<10 -10 S cm -1 ).PANI-ES prepared using first set of solvents are showing conductivity >0.3 S cm -1 , which showed FT-IR peaks close to that of PANI-H 2 SO 4 salt peaks.

Table 5 : Correlation between FT-IR peaks with conductivity and its measurement technique
a Ref No. [21-24], b Prepared in this work