Alternating Current Response Study on PANI/V2O5 Composite at Room Temperature

In the present study, an Alternating Current (AC) response of Vanadium pentoxide (V2O5) doped Polyaniline (PANI) composite was studied. Pure PANI was synthesised by the In-situ polymerisation method. The PANI/Vanadium Pentoxide (PVO) composite was prepared by physical mixing of chemically synthesised PANI with dopant in a vibration mill. The structure and morphology of the samples were characterised by XRD and SEM studies. The Alternating Current response parameters of PANI, V2O5 and PVO composites were studied in the frequency scale of 40Hz to 110MHz at room temperature. The change in the AC conductivity of the composite as compared to PANI and V2O5 was observed and discussed based on the electron-hole exchange mechanism.


Introduction
In the present scenario, conducting polymers gained the immersion of so many researchers due to their advantageous properties, listed as easy synthesis, corrosion resistance, hygroscopic and room temperature operability.Despite this, these conducting polymers have some disadvantages, namely poor chemical stability and less mechanical strength.Thus, the conducting polymers are doped or composited with metal oxide, metal and bio-polymers to overcome these disadvantages and enhance their chemical and mechanical properties [1].
In the present work, we use the critical conducting polymer polyaniline (PANI) because of its essential properties: facile synthesis, high electrical conductivity and excellent bio-compatibility.PANI is considered to make a composite with vanadium pentoxide (V2O5) and vanadium pentoxide is taken because of its essential properties like good catalytic activity and thermal stability.The composite has been prepared by physical mixing method by taking equal amounts of PANI and V2O5 (50 Wt% of V2O5 in PANI matrix).The prepared polyaniline/vanadium pentoxide (PVO) composite has characterized structural and morphological studies like XRD and SEM techniques.The AC conductivity studies were carried out for the prepared PVO composite from40Hz to 110MHz range of frequency.The change in the conductivity, loss tangent and complex plane impedance are measured and recorded [2].

Preparation of PANI
The monomer aniline is polymerised by the In-Situ polymerisation method to prepare Polyaniline (PANI).The deionised water (200 ml) and a homogeneous mixture of HCL: aniline in a 1:6 ratio were mixed and stirred for 10m in a round bottom flask.To the above mixture, 4.8g of Ammonium persulfate (APS) dissolved in 60 ml deionised water was added drop wise using a burette to the above homogeneous solution was stirred constantly using magnetic stirrer about 4-5h.Then, the above resolution was allowed to polymerise for ten hours.After the complete polymerisation, through a suction filtration process, the filtrate was collected; the filtrate was washed using acetone,1M HCL and deionised water until it got a colourless residue, then the filtrate was kept to dry in a oven for 24h at 80 • C. Finally, a green-coloured PANI powder was formed.

PVO composite
The PVO composites were prepared using a mechanical mixing technique with pure PANI with a weight ratio [0.50:0.50] in a one-hour vibration mill.

Characterization of the sample
The FTIR spectra of powdered PANI and PVO composite were recorded by employing a NICOLET 750 FT-IR spectrometer, The XRD pattern of the sample was recorded using a Siemen D-500 powder X-Ray Difractometer.

AC Conductivity Measurements
The pellets were prepared by hydraulic press applying pressure of 4 to 5 tons.The electrodes were prepared using silver contact and coated on each sides of the pellet for better electrical connection.The Impedance analyser (Make: 4294A Precision Impedance Analyzer) accounted for AC electrical parameters with a 10 Hz to 110 MHz frequency range at room temperature.The electrical measuring apparatus is depicted in Fig. 1.To criticise the structural behaviour of the pure PANI, V2O5 and PVO composite, XRD analysis was performed and depicted in Fig. 2. The typical diffraction peak of PANI showed in Fig. 2 (  The scanning Electron Microscope (SEM) images report the surface morphology of the pure PANI, V2O5 and PVO composite, represented in Fig. 3.The fashioned SEM image of pure PANI [Fig.3(a)] shows unusual spherical grains or granular shapes of conducting polymer material.Fig. 3(b) shows irregular oblong rod-like shapes of V2O5, with scattered orientation.Such type of morphologies was reported in the literature.The image of the PVO composite [Fig.3(c)] shows agglomerated morphology.This emphasize the interest to notice that the PVO composite shows perfect incorporated non-linear dispersion of V2O5 in a polymer matrix, which was successfully achieved by mechanical mixing [4].It is required to state that the enhanced conductivity of the composite has been noted as comparing with pure PANI and V2O5.The inclusion of V2O5 increases the AC conductivity; this was achieved due to extended hopping charge carriers in the composite.Mainly, V2O5 supplements in the PANI matrix enhance the conductivity of the PVO composite due to the charge polarisation effect.The V2O5 has helped most charge carriers to polarise at particular sites, which is the principal reason for enhanced conductivity [5].The conductivity values are depicted in Table .1.

AC Conductivity Response Studies
The variation of the dielectric loss with varying frequency is represented in Fig. 4(b).The loss tangent for V2O5 is very less.The loss tangent for pure PANI, bearing higher loss at initial frequencies, decreases as the frequency higherd.A similar behaviour has been absorbed in the PVO composite-this higher loss at lower frequency is due to DC conductivity losses [6,7].

6.Conclusion
The PVO composite was prepared through the mechanical mixing method.Prepared samples have been characterized using XRD and SEM techniques.The AC conductivity was found to be 6.4x10 -5 S cm -1 at room temperature for the composite in the frequency range of 40 Hz to 110 MHz The conductivity was found to be increases with increase in applied frequency.The increase in conductivity in PVO composite attributes to the extended hopping charge carriers.Such frequency dependent AC responses of the composites at room temperature are very useful in the fabrication of memory devices, energy storage devices, sensing devices, super capacitors.
a), and the diffraction peaks arriving at 2Ѳ=15 • , 19 • and 26 • confirms the semi-crystalline nature of the PANI.The sharp peaks arrived at the pure V2O5 [Fig.2(b)] identifies the orthorhombic phase, which was well agreed with the JCPDS Card NO: 75-0457.The XRD pattern of PVO composite [Fig.2(c)] clearly shows the appearance of both peaks of PANI and V2O5, exactly showing the formation of the composite [3].

Figure 4 :
Figure 4: (a) Variation of AC Conductivity of PANI, V2O5 and PVO composite; (b) Frequency dependence of dielectric loss tangent of PANI, V2O5 and PVO Composite.

Fig. 4 (
Fig.4(a) shows the variation of AC conductivity concerning the frequency ranging from 40 Hz to 110 MHz for pure PANI, V2O5 and PVO composite.It is required to state that the enhanced conductivity of the composite has been noted as comparing with pure PANI and V2O5.The inclusion of V2O5 increases the AC conductivity; this was achieved due to extended hopping charge carriers in the composite.Mainly, V2O5 supplements in the PANI matrix enhance the conductivity of the PVO composite due to the charge polarisation effect.The V2O5 has helped most charge carriers to polarise at particular sites, which is the principal reason for enhanced conductivity[5].The conductivity values are depicted in Table.1.

Fig. 5
Fig. 5 shows the Cole -Cole plots for pure PANI, Pure V2O5 and PVO Composite.The pure PANI shown in Fig. 5(a) depicts a single semi-circle that implies the Debye-Model type.The impedance plot of V2O5 shown in Fig. 5(b) is a perfect single-semicircle, which agrees with the Debye model.However, a single semicircle in the PVO composite has been observed, which follows the non-Debye type.The diameter of the semi-circles decreases compared to PANI andV2O5with increased conductivity [8-10].

Table 1 :
The AC conductivity values for the Pure PANI, V2O5 and PVO Composite.