Electrical and magnetic properties of polyaniline/Fe3O4 nanostructures
Introduction
Recently, conducting polymers such as polyaniline (PANI), polypyrrole have attracted considerable attention especially from technical interest due to their novel properties (e.g., good environmental stability, high conductivity, easy processing, light weight, low cost and so on) and potential applications in electromagnetic radiation shielding [1], [2], microwave absorbent [3] et al. A series of methods such as template synthesis [4], [5], electrospinning [6] have been reported for synthesizing micro-/nanotubes of conducting polymers. Wan et al. have proposed a template-free method to prepare tubular PANI and polypyrrole, and reported that the resulting PANI nanotubes can obviously increase electromagnetic loss at microwave frequency [3], [7], [8], [9].
Since nanocomposites often exhibit improved chemical and physical properties over their single-component counterparts, in order to realize the full potential of technological applications of inorganic nanomaterials and conducting polymers, a large number of articles have been published reporting on the polymeric nanocomposites, i.e., PANI or polypyrrole composites containing nanoparticles such as TiO2 [10], [11], ZrO2 [12], γ-Fe2O3 [13], [14], [15], [16], Fe3O4 [17], [18], [19], [20], [21], SnO2 [22], etc. Multi-component conducting polymer systems with nanoparticles of metal oxides can be tailored to exhibit, besides novel electrical, magnetic and optical properties, also good film forming and processing properties. For example, Dey et al. [11] reported that TiO2/PANI nanocomposites show a large dielectric constant. Embedding Fe3O4 particles into PANI matrix could improve the composite thermal stability [21]. Polymeric nanocomposites have potential applications in electrochromic device [23], nonlinear optical systems [24], light emitting diodes [25], photodiodes and photovoltaic solar cells [26], gas and vapor sensors [27], and magnetic storage materials [28]. Several good review articles have been written on the synthesis, characterization and applications of the polymeric nanocomposites (e.g. see Refs. [29], [30]).
In recent years, electrical properties such as electrical conductivity [13], [14], [15], [19], [20] and magnetic properties such as magnetization [13], [15], [16], [17], [18], [19], [20], [30] of iron oxide–polymer composites have been reported extensively. For instance, Gangopadhyay et al. [14] have reported temperature-dependent conductivity and thermoelectric power for Fe2O3/polypyrrole composites. Superparamagnetism was also observed at room temperature in polymer nanocomposites containing Fe3O4 or γ-Fe2O3 nanoparticles [13], [19], [30]. However, magnetoresistance (MR) and AC susceptibility of the composites especially in the form of nanowires have not been intensively reported yet.
In this article, β-naphthalene sulfonic acid (NSA)-doped PANI nanotubes and PANI/Fe3O4 nanorods were prepared by the template-free method. The electrical conductivity, magnetization and AC magnetic susceptibility as a function of temperature and magnetic field have been studied. The results indicate there could be physical interactions between the polymer matrix and embedded Fe3O4 nanoparticles.
Section snippets
Experimental
Magnetic nanoparticles were prepared according to the following procedures: 0.99 g of FeCl2·4H2O (5 mmol) in 5 ml of deionized water and 1.63 g of FeCl3·6H2O (6 mmol) in 5 ml of deionized water were mixed at room temperature. The above mixture was dropped into 200 ml aqueous ammonia solution (0.6 M) in 20 min with vigorous stirring. The pH values of the reaction mixture were kept in the range of 11–12 with the addition of a concentrated ammonium hydroxide solution. The resulting nanoparticles were
Structural characterization
Fig. 1 shows the typical scanning electron microscopic (SEM) and transmission electron microscopic (TEM) images of PANI–NSA nanotubes and PANI–NSA/Fe3O4 nanorods. The average outer and inner diameters of PANI–NSA nanotubes are 160 and 65 nm, respectively; the average outer diameters of PANI/Fe3O4 nanorods are 140 nm. In particular, some black dots (Fe3O4 nanoparticles) in diameter of 10–20 nm embedded in the nanorods are obviously observed in Fig. 1(c). Fig. 1(c) also indicates that most of the Fe3
Conclusions
In summary, conductivity, MR, magnetization and AC susceptibility of PANI/Fe3O4 nanostructures as a function of Fe3O4 content, temperature and magnetic field have been studied and discussed. The main results obtained in this paper are summarized as follows:
- (1)
The temperature dependence of resistivity of the nanostructures follows a ln ρ∼T−1/2 law. With the increase of Fe3O4 content from 0 to 20 wt%, the room-temperature conductivity decreases from 0.154 to 0.045 S/cm, and the characteristic Mott
Acknowledgement
This project was supported by the National Natural Science Foundation of China (Grant no.: 10374107).
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