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Investigation of enhanced a.c electrical conductivity of nano aluminium particles doped with polymer composite by in-situ chemical oxidation polymerization method.

INTRODUCTION

The intrinsically conductive polymers are organic polymers that conduct electricity due to their conjugated [pi]-electrons, having metallic or semiconducting behavior, good environmental stability and also interesting optical, mechanical and electronic properties [1,2]. Conductive polymer with polyaromatic backbone including polypyrrole, polythiophene, polyaniline, etc. has received a great deal of attention in the last two decades [3]. Polyaniline (PANI) is presently considered to be one of the promising conducting polymers (CP) that has been found to have a wide range of applications including biosensors owing to its lowcost, electrical properties etc. [4]. A number of metal and metal oxide particles have been encapsulated into the conductive polymer to form nanocomposites (NCs). The NCs exhibit combination of properties like conductivity, electrochemical, catalytic and optical properties [4]. The NCs are used in appli-cations like electrochromic devices, light-emitting diodes, electromagnetic interference shielding, secondary batteries, electrostaticdischarge systems, chemical and biochemical sensors [5].The present paper reports the synthesis of Pani nanocomposite by the incorporation of n-Al particles in the pani matrix. The pani and n-Alpani have been synthesized by in -situ chemical oxidation method.

This polymer hybrid nanocomposite has been characterized using FTIR, XRD, FESEM with EDX, UV- VIS and two probe technique respectively.

MATERIALS AND METHODS

1.1 Synthesis Of Polyaniline:

0.1 M of aniline was dissolved in 100 ml of de-ionized water and stirred for 15 min using a magnetic stirrer. 1M of [H.sub.2]S[O.sub.4] was added slowly from drop to the aniline monomer solution. 0.1 M of ammonium per sulphate was dissolved in 20 ml of deionised water and slowly added drop by drop for half an hour from a burette vertically to the above prepared solution. After stirring for 5 h, the solution was filtered and the residual was washed with double distilled water, methanol and acetone, and then dried in an oven at 60[degrees]C. The final product was ground into a fine powder.

1.2 Preparation Of Al Doped With Pani Nanocomposite:

To synthesize n-Alpani, 0.1M aniline monomer and 1M [H.sub.2]S[O.sub.4] were stirred with DDW, and the required quantity of nano Aluminium (Al) powder was added. The oxidant APS was added drop-wise to the anilineacid-Aluminium (Al) mixture with constant stirring. When the sample was reacted in the mixed solution of aniline--N[H.sub.4] [S.sub.2][O.sub.8]-[H.sub.2]S[O.sub.4], the color of the sample changed to light blue, revealing formation of pani through an oxidation reaction. The stirring was continued for 5h to ensure complete polymerization. A dark green n-Alpani nanocomposite was thus formed, followed by a color change to dark blue. The composite obtained was filtered and washed with distilled water and methanol to remove excess acid. The product was dried in an oven at 60 C for 12h. The dried n-Alpani composite was fine-ground using a mortar & pestle.

1.3 Characterization Techniques:

FT-IR spectra were recorded on a Bruker Alpha T FT-IR spectrometer. IR spectra of the samples were recorded at room temperature in the mid IR region of 4000-400 [cm.sup.-1].The XRD pattern was recorded using Cu Ka radiation ([lambda]=1.54060 A[degrees]) with nickel monochromatic in the range of 2[theta] from 10[degrees] to 80[degrees]. The FESEM-EDX were recorded using JEOL--Model 6390 machine. Conductivity measurements were performed by a typical Two Probe method with PSM 1735 Frequency Response Analyzer employing the pressed pellet method over the frequency range from 1 KHz to 10MHz at room temperature. Spectrum of visible light is measured using absorption spectrometer of StellarNet Inc (model EPP2000). The power of visible light is measured using Newport optical power meter (model 1916-R) and is found to be 600 mW at wavelength of 650 nm (maximum intensity of the light spectrum).

RESULTS AND DISCUSSION

2.1 Ft- Ir Analysis:

The FT-IR spectra of pure pani and n-Alpani nanocomposite is shown in Fig.1.The very strong characteristic peaks at 3741, 2361, 1504, 1296, 1151 and 1114[cm.sup.-1] are assigned to the N-H, stretching vibration, v(N-H)+ unsaturated amine, N-B-N stretching vibrations C-N stretching of secondary aromatic amine, (C=N) stretching vibration and in-plane bending vibration of C-H mode. The peaks observed in the present work matches well with pani[6-12]. A broad and smooth absorption band in the wavenumber Range from about 400900 [cm.sup.-1]reveals the formation of Al-O vibrations [13]. The additional peak appeared at 615 [cm.sup.-1] was assigned to Al-O stretching vibrations. This confirms the interaction of n-Al nanoparticle in the conducting polymer matrix [14].

2.2 Xrd Analysis:

The X-Ray patterns of the pani and n-Alpani nanocomposite are shown in Fig. 2. XRD studies showed that pani is amorphous in nature which shown in the fig.2. The broad diffraction peak at 20 = 24 is characteristic peak for pani. After doping, the samples showed crystalline nature which was confirmed by the peaks at about 20 = 37.81[degrees], 48.28[degrees], 64.32[degrees] and 70.81[degrees] for n -Alpani. These peaks were matched with JCPDS data of Aluminium file no. 04-0787. The planes corresponding to n-Alpani is (111), (220), (200) and (311) respectively. The peak shows sharp and well-defined, indicating the crystallinity of the synthesized materials. The average crystalline size of n-Alpani has been estimated to be around 31nm.

2.3 Fe-Sem Analysis:

FESEM was performed in order to investigate surface morphology of the polymers and the nanocomposite. EDAX was done to reveal the chemical composition of the samples. fig. 3 (a), (b), (c) and (d) shows the SEM and EDAX images of pani and n-Alpani with weight percentages are shown in the table 1and 2. The FESEM image of pani is spherical and aggregated globules. In the nano composites some of the Aluminium particles seems to be embedded in the polymer matrix and started coalescing due to the surface absorption property of pani. The change in morphology can be explained by the absorption and intercalation of pani on the surface of Al nanoparticle.

2.4 Uv-Vis Spectroscopy:

UV-VIS spectroscopy was employed to characterize the optical properties. Fig. 4. Shows the UV---visible absorption spectra of pani and n-Alpani composite. A strong absorption peak between 200 nm and 400 nm was clearly observed which confirmed the presence of Al nano particles. Three characteristic absorption bands are observed in the spectra of pani at 269 nm, 368 nm and 618nm wavelength, n-Alpani composite had absorption peaks at 270 nm, 371 nm and 633nm which are attributed to [pi] -[[pi].sup.*]conjugated ring systems, polaron -[[pi].sup.*] and [pi]-polaron benzenoid to quinoid excitonic transition respectively. The red shift of the absorption transition to higher wavelength may be due to the successful interaction of metal nanoparticles with the polymer chain. The band gap of the pani and nanocomposite is calculated from E=hc/[lambda] Where, E is the band gap energy, h is Planck's constant, c is velocity of light, [lambda] is wavelength of absorption. Band gap energy for pani is 2.7 eV and for n-Alpani composite is 2.58 eV. Optical conductivity of polyaniline increases in presence of aluminium nanoparticles due to the decrease in optical band gap.

The red shift of the absorption transition to higher wavelength may be due to the successful interaction of metal nanoparticles with the polymer chain. The band gap of the pani and nanocomposite is calculated from E=hc/[lambda] Where, E is the band gap energy, h is Planck's constant, c is velocity of light, [lambda] is wavelength of absorption. Band gap energy for pani is 2.7 eV and for n-Alpani composite is 2.58 eV. Optical conductivity of polyaniline increases in presence of aluminium nanoparticles due to the decrease in optical band gap.

2.5 A.C Electrical Conductivity Studies:

The A. C Conductivity measurements have been performed by a typical two probe technique. The A. C electrical conductivities of pani and n-Alpani are shown in Fig. 5. The A.C electrical conductivity of pani and nAlpani were calculated and found to be 8.2 x[10.sup.-9] S/cm and 2.15 x [10.sup.-6] S/cm respectively. When compared to pure pani there is a three order increase of conductivity in the nano metal composite. The combination of amorphous and crystalline structure in the composite material may also be the reason for improved conductivity.

Conclusions:

Pure pani and n-AlPani were synthesized by adopting a facile in -situ chemical oxidation polymerization method. The structure of pani and its composites has been confirmed by FT-IR study. The average crystalline sizes have been estimated to be around n-Alpani is 31nm.The FESEM morphology showed that the pani and nAlpani has the morphological modification due to doping and the aluminium nanocomposite is evenly distributed through the polymer matrix. The reduced band gap energy in n-Alpani nanocomposite may be reason for three order increase in the conductivity. The increased conductivity was attributed to the formation of a better charge transport network in the relatively insulating pani matrix. The improvement in the electrical conductivities of these composites is expected to enhance the potential applications of the polymer.

ACKNOWLEDGEMENTS

The author thankful to authorities of Periyar University, Salem for providing the financial support through University Research Fellowship. One of the authors thankful to CSIR New Delhi for funding the research project in this field.

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(1) G. Sowmiya, (2) G. Velraj, (3) C. Shanmugapriya

(1) Periyar University, Department of Physics, Salem-636 011, Tamilnadu, India.

(2) Anna University, Department of Physics, Chennai-600 025, Tamilnadu, India.

(3) Department of sciences, Sona college of Technology, Salem -636005, Tamilnadu, India.

Received 28 February 2017; Accepted 22 May 2017; Available online 6 June 2017

Address For Correspondence: G. Velraj, Associate professor, Department of Physics, Anna University, Chennai - 600 025, Tamilnadu, India. E-mail:gvelraj@yahoo.co.uk

Caption: Fig. 1: FTIR spectra of (a) Pani and n-AlPani

Caption: Fig. 2: XRD spectra of (a) Pani and (b) n-AlPani

Caption: Fig. 3: FESEM images of (a) Pani (b) n-Alpani and EDX spectra of (c)Pani (d) n-Alpani

Caption: Fig. 4: UV-VIS spectra of (a) Pani and (b) n-Alpani

Caption: Fig. 5: A. C electrical Conductivity of (a) Pani and (b) n-AlPani

Caption: Fig. 5: A. C electrical Conductivity of (a) Pani and (b) n-AlPani
Table 1: Elemental concentration for Pani

Element   Weight%   Atomic%

Al K      52.93     40.00
O K       47.07     60.00
Total     100.00    10.00

Table 2: Elemental concentration for n-AlPani

Element   Weight%   Atomic%

C K       55.27     69.41
O K       26.87     25.33
Cl K      0.59      0.25
Cr K      17.27     5.01
Total     100.00    100.00
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Author:Sowmiya, G.; Velraj, G.; Shanmugapriya, C.
Publication:Advances in Natural and Applied Sciences
Article Type:Report
Date:Jun 1, 2017
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