Investigation of the electric conductivity and the electromagnetic interference shielding efficiency of SWCNTs/GNS/PAni nanocomposites

doi:10.1016/j.diamond.2011.06.007

Diamond and Related Materials

Volume 20, Issue 8, August 2011, Pages 1183-1187

https://doi.org/10.1016/j.diamond.2011.06.007 Get rights and content

Abstract

This work demonstrates the fabrications and characterizations of polyaniline (PAni) composites containing single-walled carbon nanotubes (SWCNTs), graphite nanosheets (GNS), or hybrid fillers (SWCNTs/GNS). The characterization of microstructure, examination of fracture surface morphologies, and measurement of electric conductivity and electromagnetic interference shielding efficiency (EMI SE) were performed. It was found that both the electric conductivity and the EMI SE increase with filler loading, and the nanocomposites filled with 1.0 wt.% SWCNTs/GNS possessed the highest electric conductivity of 16.2 S/cm and total EMI SE of 27.0 dB. The experimental results also show that absorption is the primary mechanism of EMI SE for all of the loadings and fillers.

Highlights

► PAni nanocomposites filled with SWCNTs, GNS, or SWCNTs/GNS fillers were fabricated. ► The characterizations, electric conductivity, and EMI SE performance of the PAni nanocomposites were discussed. ► A significant improvement in EMI SE from 11.3 for pure PAni to 27.0 dB for 1.0 wt% SWCNTs + GNS nanocomposites was achieved. ► Contributions of absorption and reflection on total EMI SE of fabricated nanocomposites were discussed.

Introduction

The rapid development of electronic devices has reduced the space within which high density components must operate. This may increase the electromagnetic interference (EMI) among components, which may cause degradation or malfunction of the device. EMI shielding materials have been used to protect components from EMI radiation. Polymers having conductive fillers or metal coating are the most widely used for EMI shielding. However, metal filler with high loading is usually required for achieving excellent shielding efficiency (SE). Carbon nanotubes (CNTs) with high strength and stiffness, extremely high aspect ratio, and electric conductivity promise efficient EMI shielding at low filling [1], [2], [3], [4]. Similar to CNTs, graphite nanosheets (GNS) have also been adopted for fabricating nanocomposites because they possess high surface area, remarkable stiffness, electric conductivity, etc. [5]. Although polymer has the advantages of lightness, versatility, low cost, and easy processability, the low electric conductivity of polymer restricts its application in EMI shielding. Therefore, several efforts have been made to improve the EMI SE by introducing light-conductive fillers such as CNTs and carbon nanofibers into the matrix [1], [2], [3], [4], [6], [7]. Conductive polymer for this purpose has also been developed. Polyaniline (PAni) has become one of the most attractive polymers due to its high electric conductivity, lightness, environmental stability, and ease of synthesis [8], [9]. However, the percolation threshold of PAni is high because of low compatibility and low aspect ratio of the conducting polymer [10]. The drawback of low electric conductivity can be solved by adding conducting filler into the PAni polymer.

During the past decade, improvements in EMI SE have been achieved by introducing carbon materials, such as CNTs, graphene, and carbon fibers, into polymer matrices, such as poly(methy methacrylate), epoxy, polypropylene, polyurethane, and liquid crystal polymer [1], [2], [3], [4], [5], [6], [7], [8], [9]. Improved EMI SE has been shown to require higher filler loading. For example, EMI SE of 20 dB can be obtained at 15 wt.% filler loading [6]. High EMI SE of multi-walled CNTs (MWCNTs)/PAni composites have been developed, and it was found that absorption dominated total shielding effectiveness [8]. Recently, the electrode properties of the GNS/CNTs composites was explored, and the authors suggested that CNTs were conductive bridges for connecting GNS/PAni particles [11]. Furthermore, it was reported that composites having higher electric conductivity possessed better EMI SE [4]. Therefore, composites with high EMI SE should be obtainable once GNS and CNTs are introduced into the PAni matrix simultaneously. Yet, there has been limited examination of the EMI SE of PAni nanocomposites filled with both SWCNTs and GNS.

The primary objectives of this work are to fabricate nanocomposites that include SWCNTs/PAni, GNS/PAni, or SWCNTs/GNS/PAni and to study the morphologies and microstructure characterizations of the fabricated nanocomposites. Moreover, the EMI SE performance contributed by absorption and reflection is also analyzed.

Section snippets

Syntheses of SWCNTs and GNS

SWCNTs were synthesized using the floating catalyst chemical vapor deposition (FCCVD) method. Xylene (C₈H₁₀), thiophene (C₄H₄S), and ferrocene (Fe(C₅H₅)₂) were employed as carbon precursor, promoter, and catalyst precursor, respectively. In FCCVD, xylene is mixed with thiophene in a pre-chamber and then reacted with ferrocene under a temperature of 1200 °C in a tube furnace. The details for SWCNT synthesis can be found in our previous work [12]. In the GNS preparation, the first step is

Characterizations

The Raman shift shown in Fig. 1(A) demonstrates that the average I_D/I_G ratio of the as-synthesized SWCNTs is 0.02, indicating that the SWCNTs possess high graphitization. The peaks in the range of 100 to 300 cm^-1 represent the radial breathing mode (RBM) of the SWCNTs (inset in Fig. 1(A)). As shown in Fig. 1(B), the peaks represent C-H bending of the quinoid ring at 1168 cm^-1, C-N⁺ stretching at 1344 cm^-1, and C = C stretching at 1595 cm^-1. When PAni was reinforced by fillers, the peaks were shifted

Conclusions

This work demonstrates that electric conductivity increases with filler loading, and the nanocomposites whose PAni matrices were filled with 1.0 wt.% SWCNTs/GNS possessed the highest electric conductivity and EMI SE of 16.2 S/cm and 27.0 dB, respectively. Absorption is the primary mechanism for EMI SE, which is strongly related to electric conductivity. Moreover, PAni nanocomposites filled with hybrid fillers provided structural integrity for electron transfer, enabling them to attain the highest

Acknowledgement

This research was supported by the National Science Council through Grant No. NSC 98-2221-E-007-045-MY3 and NSC 99-ET-E-007-003-ET.

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^☆☆: Presented at the Diamond 2010, 21st European Conference on Diamond, Diamond- Like Materials, Carbon Nanotubes, and Nitrides, Budapest.

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Investigation of the electric conductivity and the electromagnetic interference shielding efficiency of SWCNTs/GNS/PAni nanocomposites☆☆

Abstract

Highlights

Introduction

Section snippets

Syntheses of SWCNTs and GNS

Characterizations

Conclusions

Acknowledgement

Carbon

Carbon

Carbon

Composites A

Mater. Chem. Phys.

J. Power Sources

Diam. Relat. Mater.

Catalysis Today

Carbon