International Journal of Innovative and Emerging Research in Engineering

Volume 3, Special Issue 1, ICSTSD 2016

488

Polypyrrole/CuO Nanocomposites: Synthesis and

Dc Conductivity

M. S. Bhendea, S. P. Yawaleb and S. S.Yawaleb a Department of Physics, Prof. Ram Meghe Institute of Technology and Research, Badnera, Amravati(M.S.) (INDIA)

bDepartment of Physics, Govt.Vidarbha Institute of Science & Humanities, AMRAVATI – 444604 (M.S.) INDIA

Email: ms.bhende@rediffmail.com, spyawale@rediffmail.com

Abstract-Polymeric materials containing nano metal oxide particles

constitute a new class of polymer nanocomposite materials. The five

different weight % of nano CuO is varied in Polypyrrole and

constitutes different PPy-CuO nanocomposite materials. TEM

images show that the grain size of CuO is found to be of the order of

15 to 100 nm and that of polypyrrole is 200 to 500 nm. Some voids

and spaces are seen in the picture. These composites were

characterized for their structure and thermal stability by TEM and

TG/DTA respectively.TEM and TGA data suggest that PPy/CuO

composites have high thermal stability due to better conformation,

compactness and reduction of grain boundary volume with copper

oxide particle loading that in parallel enhanced their DC

conductivity.

Keywords: CuO, Polypyrrole nanocomposite, DC Conductivity,

TGA, TEM.

I. INTRODUCTION

Nanocomposites made by the fabrication of nanostructured materials in conducting polymers had gained special attention in material science and active multidisciplinary research because of their excellent potential in technological applications such as toners in photocopying, micro actuators, polymeric rechargeable batteries, sensors, drug delivery electrolytic capacitors and electronic devices etc. [1-8]. These nanocomposite materials are especially important due to their bridging role between the world of conducting polymers and that of inorganic materials. This encouraged the researchers taking attempt to synthesis and characterization of polymer nanocomposites based on nano-dimensional materials and conducting polymers. Polypyrrole has attracted much interest due to its easy preparation of powders and composite with good environmental stability and higher conductivity. CuO is a semiconducting compound with a narrow band gap and used for photoconductive and photothermal applications [9]. CuO has its unique physical and chemical properties and it can be used in the synthesis of superconducting materials, to form diodes, solar cell and application as a gas sensor, etc. [10–12]. Among the oxides of transition metals, copper oxide nanoparticles are of special interest because of their efficiency as nanofluids in heat transfer application. However, the reports on the preparation and characterization of nanocrystalline CuO are relatively few to some other transition metal oxides such as zinc oxide, titanium dioxide, tin dioxide and iron oxide. In this paper, we have synthesized CuO nanoparticles with size 15-100 nm. The present study deals with the structural and electrical properties of PPy-CuO nanocomposites.

II. EXPERIMENTAL

2.1 Synthesis of PPy

Polymerization of pyrrole monomer was carried out in chemical oxidative environment. 0.1 M of FeCl3 (AR grade) was added in 100 ml methanol. After complete dissolution, about 0.2 mole of pyrrole was added drop wise under constant magnetic bar stirring for 4h.The resulting precipitate was filtered and washed with copious amount of distilled water until the washings were clear. PPy so obtained was dried by keeping in oven at 600°C for 3 h.

2.2 Synthesis of nano CuO

Nanocrystalline CuO was prepared by thermal decomposition of freshly prepared Cu(OH)2 at different temperatures. The Cu(OH)2 was prepared by reacting aqueous solutions of 0.1 M copper nitrate Cu(NO3)2 3H2O and 0.5 M sodium hydroxide. For this NaOH solution was added drop wise with constant stirring until the pH of the system reaches to 12. The resulting blue-green gel was washed several times with distilled water until free of nitrate ions. Finally the gel was dried by heating at 100ºC for 10 hours. Nano crystalline CuO was prepared by heating the copper hydroxide in air for 3 hours at 80°C temperature.

2.3 Synthesis of PPy/ CuO nanocomposites

Chemically polymerized polypyrrole and its copper oxide (CuO) nanocomposites were obtained by polymerization by using FeCl3 as oxidant in aqueous medium. 0.1 M of FeCl3 was added in 100 ml of methanol. 0.02 mole pyrrole monomer was added drop wise in solution under constant magnetic bar stirring. During stirring, 10% of CuO was added. Then it was stirred continuously for a 4 hour to obtain black precipitate. It was allowed to settle for 5-6 h. Then it was filtered and washed with water 3-4 times to remove last traces of unreacted pyrrole so that clear solution was obtained. The obtained precipitate was dried for 2-3 h at 50ºC. The copper oxide was varied in wt% as 10, 20, 30, 40 and 50% and added to the PPy solution.

The PPy nanocomposites so obtained were crushed and finely ground in agate mortar. The composite powders were pressed to form pellets of 10 mm diameter and 1–2 mm thickness by applying a pressure of 5 tons in hydraulic press. Copper electrodes were placed on opposite sides of the sample to obtain

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good electrical contacts. DC electrical conductivity of samples was measured by standard two-probe technique at temperature ranging from 313 to 383K.

III. RESULTS AND DISCUSSION

3.1 Transmission electron microscopy

Fig. 1(a) and (b) shows the TEM image of pure PPy and nano CuO. The grain size of CuO is found to be from 15 to 100 nm and of polypyrrole is 200 to 500nm.

Fig 1(a): TEM image of PPy

Fig 1(b) : TEM image of pure nano CuO TEM image of PPy shows the presence of spherical ball like morphology, connected each other in chain like form. Very high magnification of TEM images shows Copper oxide particles are of regular hexagonal shape. Some voids and spaces are seen in the picture. Figure 2 shows the selected area electron diffraction pattern (SAED) of as prepared CuO nano particles. It shows that the particles are well crystallized. The diffraction rings on SAED image proves the monoclinic structure of as prepared CuO nano particles. The image clearly shows the crystalline behavior of the sample. [13].

Fig 2 : SAED image of pure nano CuO

Fig 3: TEM picture of PPy/CuO Composites.

PPy/CuO nanocomposite particles are also of spherical nature to form multiparticle aggregates, presumably because of weak antiparticle interactions. The grain size of PPy-CuO is also found to be from 6 to 100 nm and consisting interconnected grains. Some voids and spaces are seen in the picture. This may generate the porosity at the surface of the nanocomposite film of PPy/ CuO [Fig 3].

3.2 Thermogravimetry (TG) / Differential thermal analysis

(DTA):

Fig 4: TG/DTA curves for 8 wt% PPy/CuO nanocomposites

0

10

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30

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70

0

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100

120

0 200 400 600 800 Mic

rov

olt

En

do

Do

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)

Wei

gh

t (%

)

Temperature( ⁰C)

TG

TG DTA

Y=76.360%

Y=10.830%

Sample wt=0.831mg

402.160C 8wt%CuO

50 nm

100nm

100 nm

500nm

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Thermal stability of the PPy/CuO nanocomposite was assessed from analysis of the TG and DTA curves. The 8 wt% PPy/CuO nanocomposite demonstrated one step degradation (fig.4) which was in the temperature range of 366.35 to 430ºC. Only one exothermic event is observed in the PPy/CuO thermograms. This event occurs at 402.16ºC temperature, called as glass transition temperature because at this temperature there is transition from a disordered solid to a liquid. A 10.830% weight loss occurs up to 145ºC and is related to the removal of the physically adsorbed water. The exothermic event, at 402.16C, is accompanied 84.38 % weight loss. This indicates that 72∙920 to 95.121% of the sample consisted of polymers and softeners. The

residual 4.879 to 27∙080% considered to account for metallic compounds adds as dopants [14-15]. It is observed that the total wt. loss goes on decreasing with increasing nano CuO wt % in PPy.

4.3.4 DC conductivity:

The temperature dependence of conductivity of PPy and PPy/CuO nanocomposites is presented in the form of Arrhenius plots which shows a straight line with negative slope in the temperature range 313 to 383 K is shown in figure 5. The dc conductivity follows Arrhenius equation.

𝜎 = 𝜎0 𝑒𝑥𝑝 (−𝐸𝑎

𝑘𝑇⁄ )

Fig.5: Temperature dependence of dc conductivity of PPy/CuO

nanocomposite of different wt % of CuO.

The conductivity of composites increases with increase in temperature. The conductivity measurements were carried out by a two-probe method for the different wt% of PPy/CuO nanocomposites. The room temperature conductivity varies with CuO composition. It shows the maximum conductivity to 8 wt % of CuO (Fig.6). The DC conductivity of PPy is 2.52 x 10-7 S m−1 while in PPy/CuO nanocomposites, it decreases dramatically from 3.44 X 10-4 to 3.83 X 10-10 S m−1 at 343K. The appreciable linear decrease in DC conductivity may be due to the loss of moisture by the samples, since conductivity depends on

the moisture content and environmental humidity [16-17]. Low DC conductivity of pure PPy is due to the random

orientation of its particles, poor link among the polymer chains through the grain boundaries and compactness. With increasing semiconducting CuO content means better conjugation, an improvement in compactness and coupling through the grain boundaries to facilitate the charge motion [18]. The PPy/CuO nanocomposites are inhomogeneous because of dispersion of CuO particles in the polymer composites.

Fig.6: Variation of logσ with different wt % of CuO at

343 K

At high temperature the activation energy of dipole segmental process decreases due to disturbance of the cooperative movement of segments. This explains the decrease of activation energy with increase in temperature. The activation energy is evaluated from the log σ vs 1/T plot. The activation energy values are found to be in the range of 0.215 to 0.307 eV. The activation energy is found to be minimum (0.215 eV) for 8 wt% of CuO. This indicates that the charge carriers can easily hop among the conducting networks. With increasing wt% of CuO, the conducting phase becomes more conducting and also due to additional energy levels created by hopping. Hence barrier between the particles get reduced and giving lower activation value. Hence optimized wt% is 8 wt% of PPy/CuO having maximum conductivity value 3.44 x10-4 S m-1.

CONCLUSION

PPy/ CuO nanocomposites are prepared by in-situ polymerization in presence of nano CuO. The TEM images of PPy and nano CuO clearly show the presence of spherical ball of the order of 200 to 500 nm and 15 to 100 nm respectively. TEM and TGA data suggest that PPy/CuO nanocomposites have high thermal stability due to better conformation, compactness and reduction of grain boundary volume with zinc oxide particle. Our results on conductivity for various wt % CuO in PPy are interpreted in terms of the formation of polarons. The 8 wt. % of CuO sample shows higher value of conductivity. The decrease of conductivity in the composite with the loading of 20, 30, 40 and 50% is due to increase in the loading of insulating particles of CuO. On

-7.5

-5.5

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2.6 2.8 3 3.2 3.4

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Ϭ (

S/m

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8% CuO

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20%CuO

30% CuO

40%CuO

50% CuO

100% PPY

-6.5

-5.5

-4.5

-3.5

-2.5

0 10 20 30 40 50 60

logϬ

(S/m

)Wt % of CuO

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composite formation, PPy chains are supported by the nano CuO particles which lead to improve the compactness of composites.

Acknowledgement

Authors are very much thankful to the Director, Govt. Vidarbha Institute of Science and Humanities, Amravati, for providing laboratory facilities. Authors are also very much thankful to the RSIC, IIT Mumbai for TEM and TG/DTA.

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