HUMIDITY SENSING PROPERTIES OF POLYANILINE POTASSIUM MOLYBDATE COMPOSITES-2.pdf

7/28/2019 HUMIDITY SENSING PROPERTIES OF POLYANILINE POTASSIUM MOLYBDATE COMPOSITES-2.pdf

http://slidepdf.com/reader/full/humidity-sensing-properties-of-polyaniline-potassium-molybdate-composites-2pdf 1/8

International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –

6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME

179

HUMIDITY SENSING PROPERTIES OF POLYANILINE/POTASSIUM

MOLYBDATE COMPOSITES

K C Sajjan1, Muhammad Faisal

2, Khened B.S

3and Syed Khasim

4*

1Department of Physics, Veerasaiva College, Bellary-583104, Karnataka, India2Department of Physics, PESIT South Campus, Bangalore-560 100, Karnataka, India

3Deparment of Electrical and Electronics Engineering BITM, Bellary-583104, Karnataka,India

4Department of Physics, Universityof Tabuk-71491, KSA

ABSTRACT

Polyaniline (PAni) – Potassium Molybdate (PM) (K2MoO4) composites weresynthesized by insitu chemical polymerization of aniline in the presence of fine gradedK2MoO4 particles. Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) andFourier Transform Infra-Red (FTIR) spectroscopy were used to characterize the PAni-PMcomposites. The characterization results confirm the polymerization of aniline over PMparticles which results into strong interaction between PAni and PM particles. A detailedmechanism of electric transport was analyzed using DC conductivity, Humidity sensingcharacteristics such as variation of resistance as a function of relative humidity (RH) wereanalyzed for PAni-PM composites. The composite with 50 wt% of PM in PAni exhibit betterhumidity sensing property than pure PAni and other PAni-PM composites.

KEYWORDS: Polyaniline; Polyaniline Composites; Polyaniline-Potassium Molybdatecomposites; Humidity sensors.

1. INTRODUCTION

Humidity control and monitoring are of great interest to a wide area; these includemoisture sensitive products, fresh and package food, drug storage and environmental controlfor valuable antiques or paintings etc [1, 2].Humidity sensors that are available in the marketinclude dew point, infrared, catalytic and tin oxide sensors, which may be expensive, or

INTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING

& TECHNOLOGY (IJEET)

ISSN 0976 – 6545(Print) ISSN 0976 – 6553(Online)

Volume 4, Issue 2, March – April (2013), pp. 179-186© IAEME: www.iaeme.com/ijeet.asp Journal Impact Factor (2013): 5.5028 (Calculated by GISI)

www.jifactor.com

IJEET

© I A E M E





180

require high temperature operation and consume significant amount of power and high costof maintenance [3]. Much research has been focused on the development of humiditysensitive material [4-6]. Among these are the investigations using conducting polymers such

as polypyrrole, polythiophene and polyaniline for humidity and gas sensing [7-9].Advantageswith polymers as sensing materials are light weight, flexible, low cost and simple fabricationprocess [10]. Pure polymer, polymer blends and polymer–inorganic composites have alsobeen studied for the purposes, resulting in different degree of advancements in this area [11-19]. Generally, conducting polymers behave quite similarly on exposure to humidity. Aresistance decrease (or conductivity increase) is observed due to the formation of H-bondingbetween water molecules and the nitrogen centre of the polymer backbone. This facilitatesthe proton exchanges to increase the doping level of the conducting polymer and so thenumber of charge carriers increases, resulting in an increase in conductivity [20]. Earlier wehave reported PAni/WO3 composite with better electrical and humidity sensing propertiesthan individual polyaniline and WO3 alone [18]. In the present paper we report the detailedinvestigation of electrical and humidity sensing response of PAni - K2MoO4 (PAni-PM)

composites.

2. EXPERIMENTAL

2.1 Synthesis of PAni- K2MoO4 composites

The chemical oxidative polymerization of aniline into polyaniline was carried outusing the ammonium peroxydisulphate as an oxidant in the presence of HCl as reportedelsewhere including some of our previous works [7, 13, 18, 19, 21]. PAni - K 2MoO4 composites were synthesized by adding different wt% (10, 20, 30, 40 and 50) of K2MoO4 during the polymerization of aniline by fixing the yield as we have reported in the preparationof PAnicomposites earlier [18, 21, 22]. The bulk samples were processed into circular pellets

using a hydraulic press and coated with silver paste to provide electrical contacts for variousmeasurements.

2.2 Characterization

Surface morphology of PAni, K2MoO4 and PAni - K2MoO4 composites wereinvestigated by Scanning electron microscopy using Philips XL30 ESEM. X-ray diffractionwas carried out by X-ray powder diffraction at ambient temperature for the structuralcharacterization of PAni, K2MoO4 and PAni - K2MoO4 composites. A Rigaku (RU-300) X-ray diffractometer with Cu- Kα (1.54 A0) radiation was used. The FTIR spectra of PAni,K2MoO4 and PAni - K2MoO4 composites were recorded on a Perkin-Elmer 1600spectrophotometer in KBr medium.

2.3 Measurements

The Temperature dependent conductivity was recorded using two-probe method on aKeithley - 2000 multimeter, USA. . The samples in the pellet form were used for humiditysensing. The planar resistance of the sensor was recorded by controlling the humidity in aglass chamber (fig.1) at room temperature. The humidity was first lowered by keeping CaCl2 in the chamber. Controlled water vapors at room temperature were then introduced steadily





181

for increasing the humidity inside the chamber from 20 to 95 % RH. Relative humidity insidethe chamber was monitored and measured by a standard pre-calibrated humidity meterMextech-DT-615.

Fig. 1 - set-up designed for humidity sensing

3. RESULTS AND DISCUSSION

3.1 Scanning Electron Microscopy

The SEM of PAni - K2MoO4 composite with 50 wt% of K2MoO4 in PAni is shown inFig. 2(b) which reveals the presence of K2MoO4 particles uniformly distributed throughoutthe PAni sample. The presence of capillary pores as seen from this figure facilitates thesensing mechanism for PAni - K2MoO4composites.Figure 2(b) shows the SEM of pristinePAni. The SEM shows the formation of a spongy amorphous structure. Theparticle formationin polyaniline takes place by heterogeneous nucleation.

Fig. 2 SEM ofa)PAni - K2MoO4 composite with 50 wt% of K2MoO4b) pristine PAni





182

As a result granular coral like structures are formed. As a characteristic of polyaniline,secondary nucleation [23] also takes place because of which the granular coral-like particlescome together to form aggregates.

3.2 X-Ray Diffraction Analysis

Fig. 3 shows the x-ray diffraction patterns of (a) pristinePAni, (b) K2MoO4 and(c)PAni - K2MoO4 composite with 50 wt% of K2MoO4 in PAni. The two broad peaksbetween 2θ = 20o to 30o are characteristic semi crystalline peaks of polyaniline [7, 13, 18, 19,21] as shown in Fig. 3(a) which confirms that the PAni synthesized in the present work has ashort range alignment of polymer chains. Fig. 3(b) represents the XRD pattern of K 2MoO4.

The characteristic peaks between 2θ = 25o to 32o confirms the monoclinic crystalline naturefor K2MoO4. The XRD pattern of PAni - K2MoO4 composite (with 50 wt% of K2MoO4 inPAni) is shown in Fig. 3(c). The presence of characteristic peaks of K2MoO4 in this figureconfirms that the K2MoO4 has retained its structural characteristics in the composite form.

Fig. 3 X-ray diffraction patterns of (a) pristine PAni (b) K2MoO4 (c) PAni - K2MoO4 composite with 50 wt% of K2MoO4

3.3 Fourier Transform Infra Red spectroscopy

The FTIR Spectra of pristine PAni, K2MoO4 and PAni - K2MoO4 composite with 50wt% of K2MoO4in PAni is shown in Fig. 4 . Fig. 4(a) represents the FTIR spectra of pure

polyaniline with prominent peaks around 1400 cm-1

to 1600 cm-1

results due to the stretchingof C=N and C=C of quinoid and benzonoid rings [22]. The broad peaks between 900cm-1 to1200cm-1 is due to C-N and C-C stretching frequencies [22]. The sharp and prominent peakaround 900cm-1 in the FTIR spectra of K2MoO4 shown in Fig. 4(.b) is a characteristic peakfor molybdate ascribed due to M-O-H bending mode formed due to the overlapping of molybdate and potassium [24]. The weaker bands around 3500cm-1 is due to –OH stretchingfrequency and hence shows the presence of lattice water [24]. In the FTIR spectra of PAni-K2MoO4 composite as shown in Fig. 4(c), the composite has retained all the prominent peaksthat were observed in pure PAni and the prominent peaks of K2MoO4 disappears after the





183

composite formation clearly suggests the binding of organic-inorganic components. Hencethe FTIR spectra of the composite clearly suggest the formation of strong bondingmechanism between PAnichains and K2MoO4 particles.

Fig. 4 - FTIR Spectra of (a) pristine PAni , (b)K2MoO4 and (c)PAni - K2MoO4 compositewith 50 wt% of K2MoO4

3.4 Electrical Properties

3.4.1 DC Conductivity

Fig. 5shows the variation in dc conductivity σdcas a function of temperature for PAni(inset) and PAni - K2MoO4 composites. The conductivity σdc is found to increase withincrease in temperature. The dc conductivity is seen to be of three phases. In the first phasewhere the temperature range is 20 - 100 0C, the conductivity values are almost constant andin the second phase where the temperature range is 100 - 160 0C it increases slowly and in thelast phase where temperature is in the range160 - 180 0C, a linear increment in theconductivity is observed. This behavior is perhaps due to thermally assisted hopping of polarons from one localized state to another that can be confirmed by Mott theory. Theincrease in conductivity is due to the variation in distribution of K2MoO4 particles, whichmay support more number of charge carriers to hop between favorable localized sites causingincrease in conductivity. The variation of conductivity depends on the content of K2MoO4 inPAni as shown in Fig. 6. In this figure σdc for all the composites as a function ofwt% of K2MoO4 in PAni at 3 different temperaturesis shown. From these plots it is clear that at alltemperatures, the σdc of these composites increases with increasing content of K2MoO4, as theK2MoO4 content in PAni increases, it leads to the formation of more number of conductingislands and a strong coupling interactions between PAni chain and K2MoO4 particles, leadingto increase in macroscopic conductivity.





184

Fig. 5 - Variation of σdc as a function of temperature Fig. 6 - Variation of dc conductivitywith forPAni - K2MoO4 composites concentration of K2MoO4

3.5 Humidity sensing properties

The variations in the resistance as a function of relative humidity (RH) value for PAni -K2MoO4 in the form of pellets for five different weight percent of K2MoO4 (10, 20, 30, 40 and 50wt%) are shown in Fig. 7. A laboratory set-up is designed for humidity sensing (as shown in Fig1) in which the humidity is first lowered by introducing CaCl2 in the chamber [18, 19]. Then thewater vapors are introduced in the chamber with the help of air compressor which is attached to aflask containing water in order to increase humidity inside the chamber from 20 to 95% RH. Thechange in the resistance was monitored for the composites as the relative humidity in its

surrounding was varied. The resistance of the composite was observed to decrease with increasein the relative humidity(RH%). The resistance change becomes quite significant with increase incontent of K2MoO4 in PAni. The decrease in resistance with increase in relative humidity isbecause of adsorption of water molecules by the pellet surface. Typically on exposure to watervapor, polyaniline becomes protonated, and an increase in conductivity is observed. The humiditysensing property of polyaniline to water vapor can be regarded as electron hopping assisted byproton transfer mechanism and capillary condensation of water molecules into the sample surface[25, 26]. At low humidity, under dry conditions the mobility of the K2MoO4 ion is restricted andthe polymer chains would tend to curl up into compact coil form. On the contrary, at highhumidity, the polymer absorbs water molecules and followed by the uncurling of the compactcoil, forms into straight chains that are aligned with respect to each other. This geometry of thepolymer is favorable for enhanced mobility of the K2MoO4 ion or the charge transfer across the

polymer chains and hence the conductivity increases [17, 18]. Fig 8 shows the variation of resistance with weight percent of K2MoO4 in PAnifor 5 fixed relative humidity of 30, 45, 60, 75and 90 % RH, where it was observed that as weight percent of K 2MoO4 in PAni increases theresistance decreases, hence conductivity increases. This could be due to an increase in thedisorderliness of the composite with increasing amount of K2MoO4 which is also seen from SEM.This increase in disorderedness causes higher capillary action and more amount of water beingswallowed which results into increase in conductivity. The composite with 50 wt% of K2MoO4 inPAni shows significant reduction in resistance indicating its potential to be used as a polymerbased humidity sensor.





185

Fig. 7 - Resistance as a function of relative humidity Fig. 8 - Variation of resistance withweight (RH) value for PAni - K2MoO4 composites percent of K2MoO4 in PAni

CONCLUSIONS

This paper presents hitherto unreported humidity sensing and electrical properties of polyaniline- Potassium molybdate composites synthesized by insitu chemical polymerizationtechnique. The characterization results such as SEM shows the formation of uniform, spongy,amorphous surface morphology with capillary pores which is suitable for humidity sensingapplication. The XRD spectrum of composite shows the presence of prominent peakscorresponds to K2MoO4 indicates the crystalline nature of composite in spite polyanilinebeing amorphous. The FTIR spectrum reveals the formation of composite with strong

interactions between PAnichains and K2MoO4 particles. The composite exhibit betterelectrical properties than pristine PAni as analyzed through DC conductivities. The electricalproperties in these composites show a strong dependence on content of K2MoO4 in PAni witha well observed percolation phenomenon. PAni - K2MoO4 composites exhibit pronouncedchange in resistivity with changing humid environment. The resistivity change with varyinghumidity depends on content of K2MoO4 in PAni. The composite with 50 wt% of K2MoO4 inPAnishows pronounced reduction in resistivity indicating the potential of this material to beused as a humidity sensor for practical applications.

REFERENCES

[1] E. Bracken, Sens. Rev. 17 (1997) 291–298.

[2] C.Y. Lee, G.B. Lee, Sens. Lett. 3 (2005) 1–15.[3] D. Hodgins, Sens. Rev. 14 (4) (1994) 28–31.[4] S.K. Khijwania, K.L. Srinivasan, J.P. Singh, Sens. Actuators B 104 (2005) 217–222.[5] Z.M. Rittersma, Sens. Actuators A 96 (2002) 196–210.[6] Z. Chen, C. Lu, Sens. Lett. 3 (2005) 274–295.[7] N. Parvatikar, S. Jain, S.V. Bhoraskar, M.V.N.A. Prasad, J. Appl. Polym. Sci. 102 (2006)5533–5537.[8] T. Maddanimath, I.S. Mulla, S.R. Sainkar, K. Vijayamohanan, K.I. Shaikh, A.S. Patil,S.P. Vernekar, Sens. Actuators B 81 (2002) 141–151.





186

[9] A.G. MacDiarmid, Synth. Met. 84 (1997) 27–34.[10] G. HarsaÂnyi, Sens. Rev. 20 (2000) 98–105.[11] R. Nohria, R.K. Khillan, Y. Su, R. Dikshit, Y. Lvov, K. Varahramyan, Sens. Actuators B

114 (2006) 218–222.[12] DewyaniPatil, PradipPatil, You-KyongSeo, Young Kyu Hwang, Sens. Actuators B 148(2010) 41–48.[13] N. Parvatikar, S. Jain, C.M. Kanamadi, B.K. Chougule, S.V. Bhoraskar, M.V.N.A.Prasad, J. Appl. Polym. Sci. 103 (2007) 653–658.[14] S.T. McGovern, G.M. Spink, G.G. Wallace, Sens. Actuators B 107 (2005) 657–665.[15] M.L. Singla, S. Awasthi, A. Srivastava, Sens. Actuators B 127 (2007) 580–585.[16] M. Wan, Z.X. Wei, Z.M. Zhang, L.J. Zhang, K. Huang, Y.S. Yang, Synth. Met. 135(2003) 175–176.[17] S. Jain, S. Chakane, A.B. Samui, V.N. Krishnamurthy, S.V. Bhoraskar, Sens. Actuators

B 96 (2003) 124–129.[18] N. Parvatikar, S. Jain, S. Khasim, M. Revansiddappa, S.V. Bhoraskar, M.V.N. Ambika

Prasad, Sens. Actuators B 114 (2006) 599–603.[19] Machappa T, M. Sasikala, Koppalkar R. Anilkumar and M. V. N. Ambika Prasad,Sensors and Transducers Journal 107 (2009) 77-85.

[20] J.P. Travers, M. Necheschein, Synth. Met. 21 (1987) 135–141.[21] Muhammad Faisal and Syed Khasim, Advanced Materials Research Vols. 488-489(2012) 557-561.[22] Syed Khasim, S C Raghavendra, M Revanasiddappa, K C Sajjan, Mohana Lakshmi andMuhammad Faisal, Bull. Mater.Sci 34(7) (2011) 1557-1561.[23] Dan Li and Richard B. Kaner, J. Am. Chem. Soc. 128(3) (2006) 968 – 975.[24] A. Nilchi, B. Maalek, A. Kanchi, M.G. Maragheh, A. Bagheri, Radiat. Phys. Chem.75(2006) 301–308[25] ShabnamVirji, Richard B. Kaner, and Bruce H. Weiller, J. Phys. Chem. B 110(44)

(2006) 22266-22270.[26] N. Yamazoe, Y. Shimizu, Sens. Actuators B 10 (1986) 379.[27] Khened B.S, Machappa.T, M.V.N. Ambika Prasad and Sasikala. M., “ImpedanceSpectroscopic Studies On Pani/Ceo2 Composites” International Journal of ElectricalEngineering & Technology (IJEET), Volume 4, Issue 1, 2013, pp. 1 - 8, ISSN Print : 0976-6545, ISSN Online: 0976-6553.[28] Sandeep Dhariwal, Vijay K. Lamba and Ritu Vijay, “Analyzing The TransportProperties Of Metallic Swcnt Interconnects Between Gold Electrodes” International journalof Electronics and Communication Engineering &Technology (IJECET), Volume 3, Issue 2,2012, pp. 451 - 460, ISSN Print: 0976- 6464, ISSN Online: 0976 –6472.

HUMIDITY SENSING PROPERTIES OF POLYANILINE POTASSIUM MOLYBDATE COMPOSITES-2.pdf

Documents

Transcript of HUMIDITY SENSING PROPERTIES OF POLYANILINE POTASSIUM MOLYBDATE COMPOSITES-2.pdf