Electrical and Alcohol Sensing Properties of MWCNT/PS Composites

Electrical and Alcohol Sensing Properties of MWCNT/PS Composites

Faridah Abdul Razak1,a and Roslan Md. Nor2,b

1,2Department of Physics, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, MALAYSIA

Email : [email protected], [email protected]

Keywords: Carbon nanotubes; Nanocomposites; Electrical properties; Polymers.

Abstract. Composites of polystrene and multiwalled carbon nanotubes were prepared using the

solution blending method. Results on the electrical conductivity and alcohol vapor sensing will be

presented. Field Emission Scanning Electron Microscopy was used to investigate the structure

MWCNT/PS composites. The optical characterization was investigated by Fourier Transform-

Infrared Spectroscopy. Thermogravimetric Analysis was used to determine the composition of

materials and to predict their thermal stability at temperatures up to 6000oC.

Introduction

Carbon nanotubes are long cylinders of covalently bonded carbon atoms with a diameter ranging

from a few angstroms to several tens of nanometers across. These tubes have an extremely desirable

combination of mechanical, thermal and electrical behaviors. CNT can transform an insulating

polymer into a conducting composite at very low loading because of their extremely high aspect

ratio. The simple method to fabricate Polystrene/Multiwalled carbon nanotubes (MWCNT/PS)

composite where the ethanol vapour sensing characteristics were measured.

Materials and methods

Dispersed MWCNT at loading of between 1% to 9% were added to PS to form homogeneous

composites, dried in the form of sheets where the ethanol vapour sensing properties was

investigated. MWCNT diameter is 10-30nm, length ~5-15µm and 95% pure was dispersed in SDS

solution. PS (molecular wt ~2 X 105 g/mol) was dissolved in toluene. MWCNT/PS was fabricated

by solution mixing with MWCNT loading of 1%. Ethanol vapour sensing samples were obtained

from dried MWCNT/PS composite solutions. Firstly, all apparatus must be clean. 20 ml of

deionised water was thoroughly mixed in 0.5 g of PS and stirred about 1hour until dissolved. 1% to

10% of MWCNT was added to 20ml deionised water. These selected masses are diluted and stirr 1

hour. Then, all the mixtures were mixed and put into ultrasonic bath for 30 minutes. The samples

were heated for 230C until the solution was thick around 6 hours. Printed Circuit Board (PCB) was

used to test the resistivity of the samples. Samples were dropped to PCB and run using gas sensor.

The reading of resistance was taken for 500sec while ethanol gas passing through the tube. The

reaction between nanotube and other molecules alter the electrical resistance due to the change in

molecule structure. Using this mechanism we can used MWCNT sensors as chemical detector [6,7].

Results and discussion

The electrical response of 1% MWCNT/PS and 50% ethanol concentration in Fig. 1 shows the

comparison of electrical response after exposure to different ethanol flow-rates between 20 sccm

and 100 sccm. Fig. 2 an example of electrical curves of the 9% MWCNT/PS at different

concentrations of ethanol at the same flow-rate (40 sccm). Fig. 1 shows the response and recovery

Advanced Materials Research Vol. 832 (2014) pp 178-182Online available since 2013/Nov/21 at www.scientific.net© (2014) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMR.832.178

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curves of CNT composite-based sensor under ethanol vapor concentration of 50 ppm at an

operating temperature of 38˚C.

Fig. 1: Electrical response of 1% MWCNT/PS and 50% ethanol concentration at different ethanol

flow-rate.

Fig. 2: Electrical response of 9% MWCNT/PS and flow rate=40 sccm at different ethanol

concentration.

Fig. 3: The response resistance of 1%, 3%, 5%, 7% and 9% MWCNT/PS at 50% ethanol

concentrations.

0

2000

4000

6000

8000

0 100

R

Time (sec)

20 sccm

40 sccm

60 sccm

80 sccm

100 sccm

0

5000

10000

15000

20000

25000

0 50 100

R

Time (sec)

100:00

70:30

50:50

30:70

0

5

10

15

20

25

20 40 60 80 100

R/R

o

Time (sec)

1%

3%

5%

7%

9%

Advanced Materials Research Vol. 832 179

Fig. 4: The response resistance of 1%, 3%, 5%, 7% and 9% MWCNT/PS at different ethanol

concentrations.

Fig. 5: Response sensitivity of 1% to 9% PS/MWCNT at 50% ethanol concentrations.

Fig. 6: Response sensitivity of 1% to 9% PS/MWCNT at different concentrations.

Fig. 7 shows the surface morphologies of the MWCNT/PS composite. Fig. 2a and b is the

FESEM image at high magnification. These nanoparticles have a n arrow size-distribution and

average particle size of ~2µm and ~1µm. The image at low magnification (Fig. 2c) shows relatively

clean surface with more bitty gullies for the prepared MWCNT/PS nanospheres.

0

1

2

3

4

5

6

7

1% 3% 5% 7% 9%

R/R

oTime (sec)

30:70

50:50

70:30

100:00

0

5

10

15

20

25

20 40 60 80 100

Se

nsi

tiv

ity

(%)

Presentage of volume of ethanol in

water

1%

3%

5%

7%

9%

0

1

2

3

4

5

6

1 3 5 7 9

Se

nsi

ttiv

ity

(%)

Presentage of volume of ethanol in

CNT(%)

30:70

50:50

70:30

100:00

180 Nanoscience, Nanotechnology and Nanoengineering

Fig. 7. The FESEM images of 1%, 3%, 5%, 7% and 9% MWCNT/PS at high (a)&(b) and low (c)

magnifications.

Fig. 8 shows the FTIR spectrum of 1%, 3%, 5%, 7% and 9% MWCNT/PS. The broad bands in

the wavenumber range of 3000-3500 cm-1

are related to the trace amount of deionised water in PS

used for preparation of the samples whereas the C-H strectching vibrations of the toluene can be

observed at 2922 cm-1

. The broad absorption band at 1636 cm-1

corresponds to the stretching

vibration of the C=O group of amide. The broad but relatively weak band at 1492 cm1 is assigned to

the stretching vibration of the C-N bond of the amide group.

Fig. 8. FTIR spectra of PS-MWCNTs samples.

a b c

1% 5% 3%

d

7%

e

9%

Advanced Materials Research Vol. 832 181

As shown in Fig 9, only about 1.8 wt% weight loss, mainly contributed by the decomposition of

the amorphous carbon or the residual metal catalysts, can be observed for the raw MWCNTs when

the temperature is increased to 50000C, indicating a good thermal stability of the raw MWCNT/PS.

Fig. 9. Temperature dependence of weight loss for the raw 1% to 9% MWCNT/PS composites.

Conclusion

Nanocomposites film of MWCNT/PS was prepared by blending solution providing good

nanotube dispersion in polymer. FESEM was employed to determine the nanostructure of nanotube.

The sensor sensitivity is increase with increasing the flow-rate of the ethanol vapour.

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-20

0

20

40

60

80

100

0 100 200 300 400 500 600

We

igh

t %

Temperature (deg C)

1% PS/MWCNT

3% PS/MWCNT

5% PS/MWCNT

7% PS/MWCNT

9% PS/MWCNT

182 Nanoscience, Nanotechnology and Nanoengineering

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