Effect of oxyfluorination on electromagnetic interference shielding of polypyrrole-coated multi-walled carbon nanotubes

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Abstract

The polypyrrole-coated multi-walled carbon nanotubes (MWCNTs) were prepared by in situ chemical oxidative polymerization of pyrrole on the surface of MWCNTs for the novel electromagnetic interference (EMI) shielding materials. The oxyfluorination treatment on MWCNTs introduced the hydrophilic functional groups resulting in well distribution and higher interfacial affinity between polypyrrole (PPy) and MWCNTs. The PPy phases formed on MWCNTs were observed by SEM. The thickness of PPy on the surface of MWCNTs decreased as increasing the hydrophilic groups on MWCNTs by the oxyfluorination treatment. The PPy-coated MWCNT composites showed the remarkable increases in permittivity, permeability, and EMI shielding efficiency (SE). The EMI SE of PPy-coated MWCNTs increased up about 28.6 dB mainly based on the absorption mechanism.

Introduction

Since their discovery in 1991, carbon nanotubes (CNTs) have been spotlighted as excellent materials because of their unique structural, electrical, and mechanical properties [1], [2]. One of the most important applications of CNTs is the development of polymer-based CNTs composites for industrial applications. The incorporation of CNTs into polymer has been investigated for a wide range of applications, such as aerospace structural panels, sporting goods, automotive components, organic solar cells, supercapacitors, nanosensors, electrostatic dissipation, electrostatic painting, and electromagnetic interference (EMI) shielding [3], [4], [5], [6], [7], [8], [9], [10], [11], [12].

Among these applications, EMI shielding property of CNTs was investigated in this study. EMI is generated by the interference effect of current induced by electric and magnetic fields, emanating from nearby wide range of electrical circuitry [13]. It can also cause the human diseases such as leukemia, miscarriages, and breast cancer. Therefore, the attenuation of EMI has been studied more deeply by many researchers [14], [15], [16], [17], [18], [19]. Recently, electrically conducting polymer-based conducting composites were developed for EMI shielding applications because they had distinct advantages over metals, such as light weight, corrosion resistance, and flexibility [20], [21]. Among the various conducting polymers, polypyrrole (PPy) is one of the most broadly studied conducting polymers. It shows high conductivity, oxygen resistance, thermal and environmental stabilities, relative ease of synthesis, and innoxious characteristics, which are favorable for the various applications [22], [23].

In this study, a simple procedure for the fabrication of PPy-coated MWCNTs composites was carried out by in situ chemical oxidative polymerization. Poor dispersion and lack of interfacial adhesion of MWCNTs place serious obstacles in their further development. A direct oxyfluorination method was applied to the surface of MWCNTs to solve the poor dispersion and the lack of interfacial adhesion in the conducting polymer matrices. The thickness and the uniformity of PPy coating on the MWCNTs were controlled by varying the oxygen content in the reaction gas mixtures. The effect of oxyfluorination of MWCNT on the EMI shielding behavior was investigated in terms of permittivity, permeability, and EMI shielding efficiency (SE).

Section snippets

Materials

Pyrrole monomer (99%), ammonium persulfate (APS), and MWCNTs were purchased from Sigma–Aldrich. The diameter of MWCNTs was between 110 and 170 nm and the purity of MWCNTs was higher than 90%. Sodium dodecyl sulfate as surfactant was obtained from ICN Biomedicals. Hydrogen peroxide (H2O2) was purchased from Kanto Chemical.

Surface treatment of MWCNTs

The surface of MWCNTs was modified using the direct oxyfluorination method. MWCNTs were pretreated at 120 °C for 12 h in order to remove the impurities. After evacuation, the

XPS analysis of oxyfluorinated MWCNTs

The XPS elemental survey data of the pristine and the oxyfluorinated MWCNTs are shown in Fig. 1. The XPS spectra showed the distinct carbon, oxygen, and fluorine peaks, representing the major constituents of MWCNTs investigated. In the pristine MWCNTs, carbon and fluorine elements were confirmed by the C 1s and O 1s peaks. This result indicated that the pristine MWCNTs had carbon atoms from MWCNTs and the oxygen atoms from the H2O adsorption on MWCNTs from ambient atmosphere. In the

Conclusions

PPy-coated MWCNTs composites were prepared as EMI shielding materials by in situ chemical oxidative polymerization. Hydrophilic functional groups on the surface of MWCNTs by oxyfluorination were confirmed by XPS analysis. The dispersion stability of MWCNTs was improved by oxyfluorination. PPy could be uniformly coated on MWCNTs by increasing the oxygen content in oxyfluorination condition. Hydrophilic functional group on MWCNTs by oxyfluorination resulted in the higher interfacial affinity

Acknowledgement

This study was financially supported by research fund of Chungnam National University in 2010.

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