Polypyrrole composites for shielding applications
Introduction
The rapid progress in the field of conducting polymer has inspired much interest for the technological applications in molecular electronics, sensor, battery, light emitting diodes (LED), antistatic coatings, and electromagnetic interference (EMI) shielding where lightweight, flexibility and high conductivity materials are required [1], [2], [3], [4], [5], [6], [7], [8]. The conducting polymer has been used as an EMI shielding material where circumvent disadvantages has been seen in the metals [9], [10], [11], [12]. Researches in the past have established the ability of polymer composites made with electrically conducting polymers to be suitable as a shield against the electromagnetic interference [13], [14], [15], [16], [17], [18], [19], [20], [21], [22]. Most of the studies are performed so far; conducting composites are made by adding carbon black, carbon fiber, nickel-coated graphite fiber, metal powders, or metallic particle fillers [23], [24], [25], [26]. However, because of certain disadvantages like relatively high cost and time consuming besides the galvanic corrosion phenomenon observed when dissimilar metals are joined, conducting polymer composites were being made which were found suitable for EMI shielding dissipation of electrostatic charge.
Polypyrrole (PPy) is an especially promising conductive polymer for commercial applications, due to its high conductivity, good environmental stability, and ease in synthesis. Their use as new materials has opened up entirely new field for polymeric materials. Therefore, several approaches to prepare nanocomposite consisting of magnetic nanoparticles and polypyrrole have been reported [27], [28], [29], [30], [31]. Although iron oxide–PPy composites have been successfully prepared by various methods, they still have low room-temperature conductivity, low coercive force, and their structure and properties are difficult to control. Thus, further development of synthetic methods to produce novel electrical–magnetic composites with high conductivity, high coercive force and wide frequency range is highly desirable. There is one single material, which satisfies these requirements in a wide range of frequencies; therefore, several materials and/or methods have to employ in order to achieve the desired absorption properties for EMI applications. As a result, a creation of novel synthetic methodology is necessary to develop materials response to wide range frequency with a good absorption or reflection characteristics depending on application.
Our approach is to synthesis one single particle, that combines different EMI characteristics, covers wide frequency range and is processed in a magnetic field with novel composition, resulting lighter materials. Recently, magnetic and conducting polyaniline-MnZn ferrite (PANI-MZF) microparticles with composite structure have been prepared by oxidative chemical and electrochemical polymerization technique in our laboratory [32], [33]. This work is continuation of our previous work and includes synthesis and characterization of composites by FTIR, impedance, and magnetization. Composite synthesis is performed by three elements of particles: (i) ferrite particles, (ii) a thin coating of nickel, and (iii) a thin layer of a conducting polymer (1–10 wt.%). Coating of Nickel gives high strength, low weight, high aspect ratio and better conductivity, and corrosion resistance. Due to the unprocessibility of conducting polymers with extensive delocaliztion of π-electrons, later, the materials have been processed in the form of coatings, films, and sheets as such (the polypyrrole is the binder), and by blending of conventional polymer such as polyurethane (PU) wherein the composites retain the mechanical properties of the conventional polymers and the electrical conductivity of the conducting polymers. The influence of monomer concentration, oxidation potential on the electrical and ferromagnetic properties of the PPy was investigated. The electrical and ferromagnetic properties are discussed based on the structural characterizations including, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD). Magnetic properties of particles were investigated 10–300 K-temperature range.
Section snippets
Materials
The monomer, pyrrole (Py) (Aldrich), p-tolueneslufonic acid (p-TSA, Aldirch), HCI (Aldrich), acetonitrile (ACN, Aldrich), tetraethylammoniumtetrafluoroborate (TEATFBO4, Aldrich), lithium tetrafluoroborate (LiTFBO4, Aldrich), N-methyl-2-pyrrolidinone (NMP), NiSO4·6H2O (Aldrich), NiCl2·6H2O (Aldrich), H3BO3 (Aldrich), KH2PO4 (Aldrich) were analytical grade and used without further purification. MnZn ferrite, which has high initial permeability (μi ≈ 10,000) and Ni-MnZn ferrite (Ni-MZF) were a
Instrumentation
The AC measurements were performed using electrochemical impedance spectroscopy in the 0.1–104 Hz (EG&G Potentiostat/Galvanostat, 273A), by sandwiching the samples between two stainless steel (SS) cylinders. DC conductivity of the samples was measured using the standard four-point probe technique. The principal transmission bands observed in the FTIR was carried out using Perkin-Elmer Spectrum one instrument. Magnetic characterizations of ferrite and polymer coated ferrite particles were
Synthesis of polypyrrole (PPy) in the presence of MnZn ferrite and Ni-MnZn ferrite
PPy was prepared by chemical polymerization technique of pyrrole in presence of MnZn ferrite and/or Ni-MnZn ferrite, p-toluensulfonic acid monohydrate (p-TSA), and FeCl3 at (∼0 °C), and it was kept for 4 h. PPy coated particles were collected on a filter paper, washed using the aqueous acid solution and methanol until the washings were found colorless and later, dried in the vacuum oven at 60 °C.
Electrochemical synthesis of polypyrrole in the presence of MnZn ferrite and Ni-MnZn ferrite
In the electrochemical method, for polypyrrole deposition over the magnetic core cell is shown
FTIR measurements
The FTIR spectra at transmission mode of different coated particles were measured using KBr/particles pellet. The FTIR spectra of PPy and the PPy-MZF composite are shown in Fig. 2. The characteristic absorption bands of polypyrrole are observed at 1652, 1560 and 1459 cm−1. The absorption peaks at 1652, 1560 and 1459 cm−1 were induced in the PPy-MZF composite, by the interaction of MZF and the PPy backbone. The CH in-plane vibrations at 1309, 1044 and 1190 cm−1 and CH out-of-plane vibrations at 786
Conclusions
We have studied chemical and electrochemical polymerization of pyrrole in the presence of ferrites and investigated resulting physical properties of polypyrrole (PPy) coated over MnZn ferrite (MZF), nickel coated over PPy, and PPy coated over Ni-MZF magnetic core particles which might be responsible for wide range frequency for their absorption or reflection properties. According to polymerization and coating techniques that they are used in this study, the main results are summarized as
Acknowledgements
This work is funded by the Missile Defense Agency and sponsored by the U.S. Army Space and Missile Defense Command (Contract no. DASG30-01-C-0085). Authors at USF acknowledge support from National Science Foundation through grant no. ECS-0140047.
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