Photoacoustic Measurement of Thermal Diffusivity of Polypyrrole Conducting Polymer Composite Films

© 2009 Science Publications

Photoacoustic Measurement of Thermal Diffusivity of Polypyrrole

Conducting Polymer Composite Films

1

M.Y. Lim, 1W. Mahmood Mat Yunus, 2A. Kassim and 3H.N.M.E. Mahmud 1

Department of Physics, Faculty of Science, Universiti Putra Malaysia,

43400 Serdang, Selangor, Malaysia

2

Department of Chemistry, Faculty of Science, University Putra Malaysia,

43400 Serdang, Selangor, Malaysia

3

Faculty of Chemical Engineering, Universiti Teknologi MARA,

40450 Shah Alam, Selangor, Malaysia

Abstract: The thermal diffusivity has been measured for the Polypyrrole-Polyethylene Glycol (PPy-PEG) composite films by the open photoacoustic method. The experimental data were analyzed for thermal diffusivity by fitting procedure. The different process parameters such as different concentrations of insulating polymer, monomer and electrolyte and the different voltages used to prepare the PPy-PEG composite films brought changes in thermal diffusivity. The process condition of 0.20 M pyrrole, 0.10 M p-toluene sulfonate and 1×10−3 M PEG at 1.20 volt (vs SCE) appeared as the optimum condition and the PPy-PEG composite film produced from this optimum condition shows the highest thermal diffusivity (7.88×10−7 m2 s−1).

Key words: Polypyrrole,polyethylene glycol, thermal diffusivity, photoacoustic method

Recently, Photoacoustic spectroscopy (PAS) found important applications in research and analysis of inorganic, organic and biological solids and semisolid. It is a non-destructive technique that is applicable to almost all types of samples. It offers a minimal sample preparation and has the ability to look at opaque and scattering samples. In addition it has the capability to perform depth profiling experiments. PAS can be used for both qualitative and quantitative analysis. Photoacoustic is the production of acoustic waves by the absorption of light energy. The photoacoustic effect is based on the sensitive detection acoustic waves launched by the absorption of modulated laser radiation[1-2]. The PAS constitutes a simple, very reliable, experimental tool[3] and has been widely used in measuring thermal diffusivity. The sensitivity tool of photoacoustic technique make this technique is suitable for studying the effect of synthesizing conditions in chemistry very often occurs in polymer synthesis[4-5]. In our present study, the polypyrrole-polyethylene glycol (PPy-PEG) composite films were prepared by electrochemical method[6-7].The main purpose of this

INTRODUCTION

study is to investigate the thermal diffusivity as a function of process parameters such as different concentrations of insulating polymer, monomer and electrolyte and the different applied voltages effects used to prepare PPy-PEG composite film.

MATERIAL AND METHODS

The aqueous solution in the one-compartment cell containing pyrrole monomer, p-toluene sulfonate electrolyte and the insulating polymer PEG, was electrochemically polymerized at a constant voltage (vs SCE) at room temperature for 2 h to form PPy-PEG composite film. The composite film thus produced on the ITO glass surface as an insoluble film was rinsed thoroughly with distilled water and then peeled off from the electrode. It was then dried in the oven at 60°C for 24 h. Four series of PPy-PEG film samples were prepared by electrochemical polymerization technique. In the first series we fix the concentration of polypyrrole (0.20 M), p-toluene sulfonate (0.10 M) and voltage (vs SCE) (1.2 volts) while the PEG was varied from (0.5-9)×10−3 M. Theses samples were used to study the effect of PEG concentration on thermal diffusivity of PPy-PEG composite film. From electrical

Corresponding author: Mahmood, Department of Physics, Faculty of Science, Universiti Putra Malaysia, 43400 Serdang,

Selangor, Malaysia Tel.: +6038946 6684

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Am. J. Applied Sci., 6 (2): 313-316, 2009

S=

A

exp−bf f

()(1)

where, A is a constant and b is related to the thermal diffusivity of sample, α and given as b=lsπ/α (2) By fitting the experimental data to the expression (1), the thermal diffusivity of the sample can be easily calculated.

RESULTS AND DISCUSSION

Figure 2 shows a typical photoacoustic signal as a Fig. 1: Experiment setup for OPC detection technique

function of modulated frequencies measured for

frequency range of 5 Hz-100 Hz. of PEG-Ppy measurement[8] it shown that the composite film with

−3composite sample prepared at 1.20 Volts (vs SCE). The PEG concentration of 1×10 M gives the highest

solid line is the calculated values obtained by using conductivity value. Therefore the second series of our

Eq. (1). In this case the fitting results thermal sample were prepared at fix concentration, of PEG

diffusivity of PPy-PEG sample as 7.88×10−7 m2s−1. The (1×10−3) M and let the concentration of polypyrrole

same thermal diffusivity evaluation procedure has been change from (0.10-0.40) M. Again the electrical

implied to all of our samples. The results are shown in measurement shown that the sample with 0.20 M

Fig. 3-6. concentration of polypyrrole gives the highest value of The PPy-PEG composite films prepared at various conductivity[8]. Furthermore we prepared the third

concentrations of PEG ranging from 0.5×10−3 M-9×10−3 series of PPy-PEG composite film by keeping the

M in the aqueous solution containing 0.20 M pyrrole

concentration of PEG and polypyrrole at (1×10−3) M

and 0.10 M p-toluene sulfonate at a potential of 1.20

and 0.20 M respectively and change the concentration

volt (vs SCE) has been studied to investigate the effect

of p-toluene sulfonate from 0.05 M-0.30 M. However of PEG concentration on the thermal diffusivity the in electrochemical polymerization technique the voltage films. Fig. 3. shows the thermal diffusivity increases (vs SCE) is one of the important parameter to produce a from 3.87×10−7 m2 s−1-7.88×10−7 m2 s−1 as the PEG good uniformity film and to control the thickness of the concentration in the pyrrole solution increases up to sample. With this in mind we have prepared the forth 1×10−3 M. This indicates that electron migration is an series of PPy-PEG composite at different value of addition process in thermal transport properties, voltage (vs SCE). However at higher concentration of PEG it Photoacoustic technique was used to measure shows a decreasing trend from 7.88×10−7 m2 s−1-thermal diffusivity of the prepared conducting 4.86×10−7 m2 s−1 with further increase of PEG composite films. Photoacoustic is the production of concentration from 1×10−3 M-9×10−3 M. This is in a

good agreement with the result of other polypyrrole acoustic waves by the absorption of light. This effect is

composite films reported by other researcher[12]. described as the periodic heating generated in the In the second series of samples we investigate the sample by a nonradiative deexcitation[9-11] process due

effect of pyrrole concentration on thermal diffusivity of to the absorption of a modulated light source. In this

PPy-PEG composite film. The pyrrole concentration study a heat transmission configuration known as open

has been changed from 0.10 M-0.40 M, with p-toluene photoacoustic cell (OPC) was used. The sample was

sulfonate dopant of 1×10−3 M of PEG respectively. The illuminated by the chopped laser beam which heats the

film was prepared at voltage of 1.20 Volt (vs SCE). surface and subsequently heats the gas in the cell. The

Fig. 4. shows the thermal diffusivity values as a periodic heating generates pressure variation in the

function of pyrrole concentration. A similar trend was surrounding gas medium. The experimental set up is

also observed where the higher value of thermal shown in Fig. 1.

It has been shown that at low modulation diffusivity (7.88×10−7 m2s−1) was obtained for 0.20 M frequency the photoacoustic signal for optically opaque of pyrrole concentration. The increase in thermal

[12]

samples is given by the expression. diffusivity at low 314

Am. J. Applied Sci., 6 (2): 313-316, 2009

Fig. 5: Thermal diffusivity of PPy-PEG composite

films against different p-toluene sulfonate Fig. 2: Signal fitting for PPy-PEG Composite film concentration

To investigate the effect of dopant concentration on the thermal diffusivity of PPy-PEG composite films, we have prepared the samples with the concentration of p-toluene sulfonate from 0.05-0.30 M. In presence of 0.20 M pyrrole, 1×10−3 M PEG and the voltage (vs SCE) was kept constant at 1.20 volts (vs SCE) for the whole samples in this series. The thermal diffusivity as a function of dopant concentration of PPy-PEG composite film prepared at different concentration of p-toluene sulfonate is shown in Fig. 5. In this case the highest (7.88×10−7 m2 s−1) value of thermal diffusivity was obtained for 0.10 M of dopant concentration in PPy-PEG composite film. For concentration higher than

0.10 M, the thermal diffusivity decreases with the

Fig. 3: Thermal diffusivity of PPy-PEG composite

increasing of dopant concentration. The higher thermal

films versus PEG concentration

diffusivity obtained for PPy-PEG film prepared from

0.10 M p-toluene sulfonate may due to higher conjugation length which related to the electron migration process. Since the applied potential plays an important role in electrochemical polymerization technique, we have prepared the PPy-PEG composite film by changing the potential from 0.40-1.50 volts (vs SCE). For this last series of samples we kept the pyrrole solution, p-toluene sulfonate and PEG at the concentration of 0.20 M, 0.10 M and 1×10−3 M respectively. Fig. 6. shows the thermal diffusivity of the PPy-PEG composite films obtained at different potential (vs SCE). Obviously, the sample prepared at voltage of 1.20 volts (vs SCE) gives

the higher thermal diffusivity (7.88×10−7 m2 s−1). This Fig. 4: Thermal diffusivity of PPy-PEG composite can be explained by the fact that the increasing in

films versus pyrrole concentration applied voltage, the conjugation chain length (number

of pyrrole monomer units) of PPy increases causing the concentration of pyrrole (<0.20 M) may due to the fact increase in thermal diffusivity. This decrease in thermal that the polymerization rate becomes too fast causing diffusivity at the potential above 1.20 volt (vs SCE) the increase of electron migration. may be due to overoxidation process in the sample. 315

Am. J. Applied Sci., 6 (2): 313-316, 2009

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Analytical optoacoustics spectrometry: the optoacoustic effect and thermal diffusivity, Analyst., 102: 281–292

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Electrocjemical polymerization of pyrrole. J. Cham. Soc. Chem. Commun., 635-636.

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Gill, J. F. Kwak, J. A. Logan and J. F. Rabolt. 1979. Organic metals: Polypyrrole a stable synthetic 'Metallic' polymer. J. Chem. Soc. Chem. Commun., 854.

8. Lim, M. Y., H.N.M. E. Mahmud, A. Kassim and

W. M. M. Yunus. 2007. Polypyrrole-polyethylene glycol conducting polymer composite films: Preparation and characterization. Synthetic Metals., 157:386–389

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spectroscopy of Cr3+ in Ceramic Al2O3. Mater. Sci. Eng., B41:72-75.

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Fig. 6: Thermal Diffusivity of PPy-PEG composite

films against different applied voltage (vs SCE)

Thermal diffusivity of PPy-PEG composite films prepared by electropolymerization was investigated using open photoacoustic technique. The PPy-PEG composite films prepared at 0.20 M pyrrole monomer, 0.10 M p-toluene sulfonate dopant and 1×10−3 M PEG at 1.20 volt (vs SCE) gives the highest thermal diffusivity (7.88×10−7 m2 s−1).

ACKNOWLEDGEMENT

The authors would like to thank the Malaysia Government for financial support. The laboratory facilities provided by the Department of Physics, UPM are also acknowledged.

REFERENCES

1. Lu. Y. 1988. Solitons and Polaron in Conducting

Polymer. World Scientific, New Jersey, pp:74.

2. Heeger, J., S. Kivelson, J. R. Schriefer and W. P.

Su. 1988. Solitons in conducting polymers. Mod. Phys.,60: 781-850.

CONCLUSION

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