Graphene Nanocomposites for Electromagnetic Interference Shielding

Graphene Nanocomposites for Electromagnetic Interference Shielding

Available online at www.sciencedirect.com ScienceDirect Procedia Materials Science 10 (2015) 588 – 594 2nd International Conference on Nanomaterials...

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Available online at www.sciencedirect.com

ScienceDirect Procedia Materials Science 10 (2015) 588 – 594

2nd International Conference on Nanomaterials and Technologies (CNT 2014)

Synthesis and characterization of conducting polyaniline/graphene nanocomposites for electromagnetic interference shielding Prerana Modaka, Subhash B. Kondawara*, D.V. Nandanwarb a

Department of Physics,Polymer Nanotech Laboratory, Rashtrasant Tukadoji Maharaj Nagpur University, Nagpur-440033, India b Department of Physics, Shri Mathuradas Mohata College of Science, Nagpur-440023, India

Abstract Polyaniline (PANI)/graphene (GN) nanocomposites were synthesized by in-situ chemical oxidative polymerization method. A series of nanocomposites have been synthesized by varying the concentration of functionalized graphene (1%, 3% and 5%). The as-prepared nanocomposites were characterized by XRD and SEM. The results showed favorable interaction between PANI and GN. The electrical conductivity of nanocomposites was found to be drastically increased as compared to that of pure PANI at room temperature. Further the conductivity of nanocomposites was also found to be increased with the increase in weight % of GN. Nanocomposites showed semiconducting nature as that of PANI with improved properties for EMI shielding. The EMI shielding effectiveness (SE) of nanocomposites was found to be increased with increasing GN content and it was found to be absorption dominated indicating PANI/GN nanocomposites can be used as lightweight EMI shielding materials to protect electronic devices and components from electromagnetic radiation. © Published by Elsevier Ltd. This © 2015 2015The TheAuthors. Authors. Published by Elsevier Ltd. is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the International Conference on Nanomaterials and Technologies (CNT 2014). Peer-review under responsibility of the International Conference on Nanomaterials and Technologies (CNT 2014)

Keywords: Polyaniline, Graphene, Nanocomposites, Electrical Conductivity, EMI shielding * Corresponding author Tel.: +91-712-2042086; E-mail address: [email protected]

1. Introduction Electromagnetic interference (EMI) shielding belongs to the class of an intelligent packaging. EMI is an undesirable electromagnetic induction triggered by extensive use of alternating current or voltage which produces corresponding induced signals in the nearby electronic circuit and tries to spoil its performance (Saini and Arora, 2012). The electromagnetic interference can be reduced by applying a shielding material between source of electromagnetic field and the sensitive components (Singh et al, 2012). Electromagnetic radiation also adversely

2211-8128 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the International Conference on Nanomaterials and Technologies (CNT 2014) doi:10.1016/j.mspro.2015.06.010

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affects human health. Hence, efforts were made to reduce its effect using EMI shielding materials. Traditionally, metals, in the form of thin sheets or sheathing, were used as EMI shielding materials. However, metals were expensive, heavy, prone to corrosion and difficult to process. Hence, conducting polymers and composites containing conductive fillers were developed as an alternative EMI shielding material. These materials are light weight, cheap, resistant to corrosion and easily processable (Choudhary et al, 2012). In the last four decades, conducting polymers (CPs) have gained a special status owing to wealth of applications. The EMI shielding and microwave absorption properties of these polymers can be explained in terms of electrical conductivity and presence of bound/localized charges (polarons/bipolarons) leading to strong polarization and relaxation effects. Polyaniline (PANI) has special status among other conducting polymers due to its non-redox doping, good environmental stability and economic feasibility (Ghosh et al, 2012). The properties can be further tuned by controlled polymerization conditions and using substituted anilines, specific co-monomers, dopants and fillers. PANI has low inherent specific strength and requires dispersion in some binding matrix to form composites for any commercially useful product. However, percolation threshold tends to be high due to low compatibilities, phase segregated morphology and low aspect ratio of the conducting polymer particles. Therefore, high concentration of conducting polymers is required in matrix for acceptable electrical properties which often affect the mechanical properties of resultant composites. To combine the good properties of carbon nanotubes (CNTs) and PANI, several attempts have been made to introduce CNTs into PANI matrix (Saini etal, 2009). The two dimensional graphene is a promising conductor because of optical and electrical properties. In principle, electrons in individual graphene sheets delocalize over the complete sheet, which provides ballistic charge transport (Wu et al 2008). Graphene is a single layer two dimensional sheet of Sp 2 bonded carbon shows unique properties such as the quantum hall effect, high carrier mobility, good optical transparency, high young’s modulus and excellent conductivity (Kim et al 2013). Li et al (2014), studied Graphene and its composites with nanoparticles for electrochemical energy applications. Notley and Evans (2014), studied aqueous processing of graphene–polymer hybrid thin film nanocomposites and gels. Graphene based conducting polymer composites shows superior properties as compared to neat polymers (Das et al, 2013). It is reported that the PANI composite containing 5.0 wt.% Ag/graphene shows the best electrical conductivity of 20.32 S/cm and highest EMI Shielding Effectiveness (SE) of 29.33 dB. The uniform dispersion of fillers significantly enhanced the formation of conductive pathways in the PANI matrix, and the presence of metal nanoparticles on the graphene surface and between the graphene layers also increases the electrical conductivity (Chen et al.2013). It is reported that the EMI shielding efficiency of 15 wt.% graphene filled epoxy composites to be 21 dB, which is higher than the target value (20 dB) for commercial applications (Kuilla et al. 2010). However, in the present work we prepared the composite of graphene nanosheet (GN) coated with PANI by an in-situ chemical oxidative polymerization method to improve the EMI SE. 2. Experimental 2.1. Materials Aniline (99%), ammonium persulfate, sulphuric acid and nitric acid were procured from Merck Ltd., India. Graphite flakes were made available from National Physical Laboratory, New Delhi (India). All chemicals were of AR grade and used as received except aniline which was distilled under reduced pressure and kept below 4 oC before used for synthesis. Deionised water was used in all synthesis. 2.2. Synthesis of Graphite Oxide (GO), Graphene Nanosheets (GN) and Functionalization of GN Graphite Oxide (GO) was synthesized using graphite flakes by Hummers method and Graphene Nanosheets (GN) were prepared by exfoliation of GO (Bai et al,2009). In a typical method, requisite amount of graphite flakes and NaNO3 were mixed with H2SO4. Under vigorous stirring, potassium permanganate was added slowly to the suspension in 1 hour. The reaction system was stirred at room temperature for forming a thick paste. As the reaction progressed, the mixture gradually became pasty, and the colour turned into light brownish. At the end, H2O2 was slowly added to the pasty with vigorous agitation turning the colour of the solution from brown to yellow. Then the GO was suction filtered, washed with deionized water. Exfoliation was carried out by sonicating the GO dispersion under ambient condition for 30 min. For the preparation of grapheme nanosheets, ammonia solution and hydrazine

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monohydrate were added to sonicated GO dispersion, and then the mixture was heated at 90 oC for 2 hours under vigorous stirring. Once the reaction was completed, the reduced graphene nanosheets (GN) were collected by filtration as a black powder. The graphene nanosheets have limited surface functional groups on the surface for making the chemical interaction with polymer. Therefore GN was functionalised by acid treatment. For the functionalization of GN, the solution of 6M H2SO4 and 6M HNO3 in 3:1 ratio was stirred for 10 minute. GN was added to it and then solution was sonicated for 4 hours at 50 oC. After centrifugation GN was filtered, washed and dried to get functionalized GN (Georgakilas et al. 2012). 2.3. Synthesis of PANI/GN composites The GN/PANI composites were synthesized by an in-situ polymerization of aniline in the presence of GN (Ghosh et al. 2012). The weight percent of GN to aniline was varied from 1% to 5%. The solution of 0.2M H2SO4 in 50 ml of deionised water was divided into two parts. In one part 0.2M aniline and functionalised GN was added and the mixture was ultrasonicated for 30 min. After the ultrasonication the mixture was kept for stirring for about 5 hrs at 5ºC to get the better yield. To another part 0.2M ammonium persulphate (APS) was mixed and added drop by drop to the stirring monomer solution. After mixing the reactants, the solution starts showing greenish tint and afterward it turns violet. The black precipitate was obtained after 6 to 7 hrs. This precipitate was kept for overnight and diluted with deionised water until the filtrate became colourless. Finally, it was washed with ethanol and dried overnight in oven at 80ºC. 3. Results and discussion 3.1. Morphology In order to observe the surface of GN/PANI composites, SEM image of 1% GN in PANI matrix was obtained using scanning electron microscope. Fig. 1 shows the SEM image of 1% GN/PANI composite. It can be seen from the figure that most of GN surface was coated with a smooth thin polyaniline layer and some regions of the surface of GN were deposited by polyaniline.

Fig. 1: SEM image of 1% PANI/GN composite

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3.2. X-ray diffraction XRD pattern of 1% GN/PANI and 3% GN/PANI nanocomposites are shown in Fig. 2(a) and (b) respectively. The composites show the characteristic peaks of both PANI and GN without any additional bands indicating absence of covalent interactions between the phases. When GN mass percentage increased in the composites, the composites showed crystalline peaks similar to that observed from individual PANI. However, the diffraction peak of GN at 42.8o disappears, implying that the PANI and GN have been completely interacted. In the case of GN 3%, the intensity of crystal planes of PANI decreases, indicating that the PANI content of the composites decreases. The results show favorable interaction between PANI and GN. The slight shifting in the peak positions may be ascribed to charge transfer interactions between PANI and GN leading to variations in chain packing and configurations. 3.3 Electrical conductivity The electrical conductivity of nanocomposites was measured by four probe method. The samples were prepared as round shaped pellets at room temperature. The resistivity of the sample is measured by equation (1). (1) Where, w is the thickness of the sample, s is the distance between two probes and the factor G 7(w/s) is the appropriate value of (w/s) of reference semiconductor sheet. The conductivity was calculated as σ = 1/ρ. Thus, conductivity for various temperatures was calculated by measuring voltages at different temperature for constant current of 2mA. The electrical conductivity of PANI-GN composites was found to be increased for increased in weight percent of GN in PANI matrix as shown in Fig. 3. It was also observed that 1%PANI-GN showed lesser conductivity as compared to that of pure PANI and other composites. These results show that higher concentration of GN gives good networking electrical conduction because GN has high electrical conductivity. The electrical conductivity of nanocomposites was found to be drastically increased as compared to that of pure PANI at room temperature. Further the conductivity of nanocomposites was also found to be increased with the increase in weight % of GN. Nanocomposites showed semiconducting nature as that of PANI with improved properties for EMI shielding.

Fig. 2: XRD pattern of (a) 1% GN/PANI nanocomposites and (b) 3% GN/PANI nanocomposite

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Fig. 3: Electrical conductivity of PANI–GN composites versus loading levels of GN.

3.4 EMI shielding The shielding effectiveness (SE) measurement was carried out in the frequency range of 2 to 12 GHz. The total shielding effectiveness (SET) of the shield material was determined by equation (2).

(2) Where PI (EI or HI) and PT (ET or HT) are the intensity (electric or magnetic field) of incident and transmitted electromagnetic waves through a shielding material respectively. EMI SE of a material is defined as the attenuation of propagating electromagnetic waves produced by the shielding materials. Thus, the total EMI SE (SET) can be represented by sum of contributions from absorption loss (SEA), reflection loss (SER) and multiple reflections (SEM). Hence, SET is described in decibels and can be expressed by equation (3). (3) The multiple reflections (SEM) are the positive and negative correction term induced by the reflecting waves inside the shielding barrier (Pande et al, 2009, Udmale et al. 2013). The EMI shielding effectiveness was measured by network vector analyzer. Fig. 4 shows the effect of GN loading and frequency on the EMI SE of PANI-GN composites. From the figure, we can say that the EMI SE of composites is almost independent of frequency; however SE increased with increasing GN content. The high value of EMI SE is obtained for composites indicating it is higher than the required value of EMI shielding effectiveness (20 dB) for commercial applications. Such a high value of EMI SE at sufficiently low loading of GN shows the efficiency of compounding technique (i.e.good dispersion) and excellent properties of GN like high conductivity and large surface to volume ratio. The maximum value of EMI SE obtained at 5% (w/w) GN loading is between 51-52 dB in the measured frequency range. The increase in EMI SE with increasing frequency is due to decrease in skin depth (depth at which the field drops to 1/e of its original strength) of the material with increasing frequency (Colaneri and Shacklette, 1992). The EMI shielding effectiveness (SE) of nanocomposites was found to be increased with increasing GN content and it was found to be absorption dominated indicating PANI/GN nanocomposites can be used as lightweight EMI shielding materials to protect electronic devices and components from electromagnetic radiation.

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Fig. 4: EMI shielding effectiveness with respect to frequency for different wt% of GN in PANI

4. Conclusion Polyaniline (PANI)/graphene (GN) nanocomposites were successfully synthesized by in-situ chemical oxidative polymerization method. The favorable interaction between PANI and GN was confirmed by XRD and SEM characterizations. The electrical conductivity of nanocomposites was found to be drastically increased as compared to that of pure PANI at room temperature. The EMI shielding effectiveness (SE) of nanocomposites was found to be increased with increasing GN content and it was found to be absorption dominated indicating PANI/GN nanocomposites can be used as lightweight EMI shielding materials. References Bai H., Xu Y., Zhao L. , Li C and Shi G. 2009. Non-covalent functionalization of graphene sheets by sulfonated polyaniline Chemical Communication., 1667-1669 Chen Y, Li Y., Yip M, Tai N., 2013. Electromagnetic shielding efficiency of polyanilline composites filled with grapheme decorated with metallic particles,Composites Science and Technology, 80, 80-86 Colaneri, N.F., Shacklette, L.W., 1992, EMI shielding measurements of conductive polymer blends. IEEE Trans. Instrum. Meas., 41(2), 291–297. Choudhary V., Dhawan S.K. and Parveen Saini, 2012. Polymer based nanocomposites for electromagnetic interference (EMI) shielding, EM Shielding – Theory and Development of New Materials, 1-33 Das, T. K. and Prusty S., 2013, Graphene-Based Polymer Composites and Their Applications, Polymer-Plastic Technology and Engineering, 52, 319-331 Domingues S. H., Salvatierra R.V., Olveira M. M., Aldo J.G.Zarbin A. J.G., 2011. Transparent and conductive thin films of graphene/polyaniline nanocomposites prepared through interfacial polymerization, Chemical communication, 47,25922594 Georgakilas V., Otyepka M., Bourlinos A.B., Chandra V., Kim N., Kemp K. C., Hobza P., Zboril R, and Kim K.S., 2012. Functionalization of Graphene: Covalent and Non-Covalent Approaches, Derivatives and Applications ,Chemical Review. Ghosh D, Giri S, Kalra S, Das C, 2012. Synthesis and Characterisations of TiO2 Coated Multiwalled Carbon Nanotubes/Graphene/Polyaniline Nanocomposite for Supercapacitor Applications, Applications Open Journal of Applied Sciences, 2, 70-77

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