Fabrication, characterization and X-band microwave absorption properties of PAni/Fe₃O₄/PVA nanofiber composites materials

2.1 Aniline dimer-COOH preparation

The preparation aniline dimer-COOH was carryout under 200-ml round bottom flask using mechanical stirrer. 0.721 g of N-phenyl-1, 4-phenylenediamine and 3.5 g of succinic anhydride were dissolved into a 30 ml of dichloromethane (CH₂Cl₂) under mechanical stirrer for a period of 5 h. As the reaction attend some period of time, the white grey precipitate was achieved, finally, the precipitate was washed, filtered and then dried in the vacuum for 24 h.

2.2 Synthesis of magnetite (Fe₃O₄) nanoparticles

The magnetite (Fe₃O₄) nanoparticles were prepared through a chemical co-precipitation method. 5.4 g of FeCl₃ and 3.18 g of FeCl₂ were added into 100 ml of deionized distilled water under vigorous magnetic stirrer at 50 °C for 1 h. 10 ml of ammonium (NH₄) was added subsequently followed by addition of aniline dimer-COOH in 5 ml of acetone. The solution was allowed to proceed for a period of 1.5 h obtained stable water-based suspension. The precipitated was allowed to cool to room temperature and washed with water and ethanol and then dried in the vacuum for 12 h at 60 °C.

2.3 Synthesis of PAni/Fe₃O₄ nanocomposites

Ultrasonic dispersion method was employed to prepare PAni/Fe₃O₄ nanocomposites as explained in our previous work (Takai et al., 2018). Some quantity (0.2 ml) of aniline monomer was dispersed in 5 ml of H₃PO₄ in 10 ml of distilled water under ultrasonic disperser, then Fe₃O₄ nanoparticles at different weight ratio (5, 10, 15, 20, 25 wt%) disperse in the above solution to obtained aniline/Fe₃O₄ emulsion at ambient temperature. Separately 0.46 g of APS in 5 ml of H₃PO₄ disperse in 15 ml of distilled water and then added to the above solution dropwise and the reaction maintained under ultrasonic disperser for 4 h to the obtained suspension of Polyaniline containing modified Fe₃O₄ nanoparticles. Therefore, the suspension was repeatedly washed different solvent such as ethanol and acetone in order to obtained pure PAni/Fe₃O₄ nanocomposites and dried at room temperature for 12 h.

2.4 Electrospinning solution

As synthesized PAni/Fe₃O₄ nanocomposites were dispersed in 15 ml of Dimethyl sulfoxide (DMSO) under vigorous magnetic stirring process for a period of 1.5 h at ambient temperature to achieve a homogeneous solution of polyaniline contain a different weight ratio of Fe₃O₄ nanoparticles. Then 10% w/v of polyvinyl alcohol (PVA) was dissolved in 20 ml of distilled water under stirrer throughout the night to the obtained thick solution of PVA, furthermore, the solution of PAni/Fe₃O₄ nanocomposites in DMSO was further blended in the thick PVA solution to achieved electrospinning solution.

2.5 Electrospinning setup

During electrospinning techniques, traditional electrospinning apparatus was used to fabricate PAni/Fe₃O₄/PVA nanofibers composites, 10 ml solution of PAni/Fe₃O₄/PVA composites were loaded in the syringe and subsequently pump through the round head needle of the electrospinning apparatus. The DC power supply was connected across the needle and rotating collector, the flow of polymer solution was controlled using a syringe pump, while tip to collector distance was also recorded. Therefore, the uniformly deposited nanofibers were obtained and then dried in vacuum for 1 h at 30 °C, single nozzle schematic illustration of the electrospinning apparatus is shown in Fig. 1.

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Fig. 1

Schematic illustration of the electrospinning method.

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2.6 Characterization

The morphologies of PAni/Fe₃O₄/PVA nanofiber composites contain different level of Fe₃O₄ nanoparticles were investigated by Field Emission Scanning Electron Microscopes (FESEM) (JEOL JSM-7600F). The average diameter of the nanofiber was measured from FESEM images using Image J software (National Institute of Health, USA) from 100 fibres. Transmission Electron Microscope (TEM) (FeiTecnia G2-STWIN) was used to study the internal morphology of the composite nanofibers. The phase structure of the PAni/Fe₃O₄/PVA nanofiber composites was estimated using X-ray diffraction analysis (XRD) at a radiation wavelength of (λ = 0.154 nm) on X-pert pro MPD diffractometer using Cu Kα radiation. Fourier Transformation infrared spectroscopy (FTIR) was used to record the molecular structure and functional group of PAni/Fe₃O₄/PVA nanofiber composites samples (Nicolet 560 FTIR spectrometer). The microwave absorption of all sample was investigated by HP Vector Network Analyzer (Model 851ES) in the frequency range of 2–13 GHz at room temperature. The entire samples were cut into a rectangular shape (22.86 × 10.16 mm) to fit in rectangular wave-guide of X-band. The conductivity of PAni/Fe₃O₄/PVA nanofiber composites containing a different weight ratio of Fe₃O₄ nanoparticles (5, 10, 15, 20, 25%wt) was measured by standard four-point probe apparatus (Guangzhou semiconductor materials) at ambient temperature. The magnetic properties of the magnetite nanoparticles, as well as PAni/Fe₃O₄/PVA nanofiber composites, were measured using vibrating sample magnetometer (VSM) JDM-1 in the magnetic field of 10KOe at room temperature.

3.1 Morphology analysis

The morphology of the prepared nanofibers composites textiles materials recorded on Field Emission Scanning Electron Microscopes (FESEM) and Transmission Electron Microscope (TEM) is showed in Fig. 2. The PAni/Fe₃O₄/PVA nanofiber composites solution were loaded on 10 ml syringe and the electrospinning parameters were set at 16 kV volt, flow rate 0.3 ml/h and 10 cm tips to the needle to collector distance. The obtained results evidently revealed that the magnetite nanoparticles were spread all over the composites nanofibers materials (Kizildag et al., 2013; Liu et al., 2013). Furthermore, the magnetite nanoparticles was partially agglomerated on the surface of the nanofiber composites materials, it was further confirmed from the TEM results the primary accumulation of magnetite nanoparticles on the nanofiber surface was effectively prevented. The PAni/Fe₃O₄/PVA nanofiber composites size was found to increase with addition of Fe₃O₄ nanoparticles in the composites nanofibers as shown by TEM image, in order to confirm the actual diameter of the composites nanofibers, image-J computer software are used in our research and the result revealed as inserted in the Fig. 2, the composites nanofibers was found to be snowballing with addition of Fe₃O₄ nanoparticles in the composites nanofibers. The average diameter of the composites nanofibers were found to be in the range of 67 to 195 nm which is almost similar to that obtained using FESEM particles analysis. Moreover, embedding more number of Fe₃O₄ nanoparticles usually lower the solution viscosity and therefore the electrospinning of these may be hinder due to low viscosity as the solution would likely to spray on the collector instate of spinning, these lead to the formation of nanofiber with different diameter. Therefore, these ascribed to the facts that the addition of nanoparticles leads to the formation of more droplet on the collector, but in rare cases droplet are enforce to squish due to electrostatic force which result in the formation of nanofiber with different diameter, while some part of the nanofiber travel directly of the collector cover with aluminum foil paper which causing grip of the composites nanofibers textiles materials (Shahi et al., 2011; Hasrul et al., 2015).

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Fig. 2

FESEM image of PAni/Fe₃O₄/PVA nanofibers composites with different content of Fe₃O₄ nanoparticles spinning with 10 ml (16 kV, 0.3 m/h and 10 cm) with image-J software result inserted in the FEWEM image.

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The process of electrospinning was theoretically influenced with the amplification of the electric field which leads the jet to accelerate more and become stronger with the influence of repulsive force (Ngadiman et al., 2017). The diameter of the composites nanofiber has increased significantly over the increase of electrospinning applied volt. The size of the composites nanofibers has been influenced by different loading of Fe₃O₄ nanoparticles, these variations of the diameter were also ascribed by electrospinning applied volt to the extent that the electrospinning voltage makes the Taylor cone to be less stable to toward the formation of homogeneous composites nanofibers materials (Ngadiman et al., 2017; Song, 2017). The optimum electrospinning applied volts was found to be 16 kV as the electrospinning composites nanofibers are mostly homogeneous with almost 90% are in the range of 152–195 nm as revealed in Fig. 2.

3.2 Crystalline phase analysis for PVA, PAni/PVA and PAni/Fe₃O₄/PVA nanofibers composites

It’s well known that most polymers are not entirely crystal because the chains or parts of the chains have no order to the arrangement of their chain, therefore a polymer has two phases, crystalline portion and the amorphous portion (Song, 2017). The existence of the amorphous portion leads to the appearance of characteristic amorphous halos in a different pattern. The crystalline phase of PVA, PAni/PVA and PAni/Fe₃O₄/PVA composites nanofibers textile are determined by X-ray diffraction spectra (XRD) and the results are shown in Figs. 3 & 4 (10 ml spinning solution at 16 kV spinning voltage).

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Fig. 3

XRD plot of PVA and PAni/PVA composites nanofibers textile prepared at 0.3 ml/h, 10 cm tips to collector distance.

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Fig. 4

XRD plot of 10 ml solution of PAni/Fe₃O₄/PVA nanofibers composites prepared at 0.3 ml/h, 10 cm tips to collector distance with different content Fe₃O₄ nanoparticles.

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Generally, the XRD pattern of all the samples of PAni/Fe₃O₄/PVA composites nanofibers textile with different contents of Fe₃O₄ nanoparticles shows similar XRD diffraction pattern due to the fact that the phase structure of the composites nanofiber textile materials didn’t change with the influence of electrospinning parameters.

Furthermore, Fig. 3 record the existence of PVA and PAni/PVA nanofibers composites textile on X-ray diffractometry from 20 to 90° and 10 to 90° for PAni/Fe₃O₄/PVA composites nanofibers textile as seen in Figures (3 & 4). The phase structure that is identical to the Joint Committee on Powder Diffraction Standards file (JCPDS: 98–5970) with phase appear for each composite. The X-ray diffraction patterns of Fig. 3 clearly shows that the PVA and PAni/PVA composites nanofibers textile indicate amorphous behaviour with minor peaks at 2θ = 24.13°, 32.13°, 37.14° and 54.33° which represent the characteristic of doped PAni in the matrix. The peak at 24.13° is attributed to the periodicity parallel and perpendicular of the polymer chain direction of PAni matrix (Song, 2017; Yu et al., 2016). Additionally, the XRD pattern of the entire sample of PAni/Fe₃O₄/PVA nanofiber composites with different loadings of Fe₃O₄ nanoparticles showed an X-ray diffraction pattern similar to 10 to 90°, and the phase structure was identical to the Joint Committee on Powder Diffraction Standard file (JCPDS: 98–3860) which indicate the phase of each composite. The X-ray diffraction pattern clearly evaluates that all PAni composites exhibit amorphous behaviour with a small peak at 2θ = 24.13°, which represents the characteristics of PAni doped in the matrix (Yu et al., 2016; Quan et al., 2017).

The XRD patterns of PAni/Fe₃O₄/PVA composite nanofibers show their amorphous properties under different amounts of Fe₃O₄ nanoparticles (5, 10, 15, 20, 25 wt%). This is attributable to the higher content of PAni and PVA in the nanofibers composite, and the XRD results obtained in this study are consistent with those acquired by the other group (Li, 2018; Quan, 2018). In addition, the entire PAni/Fe₃O₄/PVA composite nanofibers show that PVA is present by indicating the peak at 2θ = 23.2°, also by the presence of Fe₃O₄ was confirm by assigned the peak at 2θ = 32.94°, 35.63°, 43.33°, 57.39°, 58.15°, 62.23°, 63.93° and 71.9° (Quan, 2018).

Therefore, it can be considered that the addition of magnetic materials (Fe₃O₄ nanoparticles) does not affect the chemical structure of PAni/Fe₃O₄/PVA nanofibers composite, as all PAni/Fe₃O₄/PVA composite nanofibers show almost the same FTIR and XRD spectrum. In addition, no characteristic diffraction peaks of any other impurities were detected. XRD analysis of PAni/Fe₃O₄/PVA composite nanofibers showed that the composite nanofibers contained Fe₃O₄ nanoparticles, as shown in Fig. 4. However, due to the encapsulation of PAni, the relative intensity is reduced compared to the pure Fe₃O₄ nanoparticle peak (Quan, 2018; Estevez, 2018)

3.3 Chemical bonding analysis for PVA, PAni/PVA and PAni/Fe₃O₄/PVA nanofibers composites

FTIR analysis were used to investigate the synthesized PVA, PAni/PVA and PAni/Fe₃O₄/PVA composites nanofibers textile and also to understand the existence of surface functional groups in metal interactions with polymers. Figs. 5 & 6 represents the FT-IR spectra of PVA, PAni/PVA and PAni/Fe₃O₄/PVA composites nanofibers textile material spinning at different parameters such as flow rate, applied voltage and tip to collector distance respectively. A weak intense peak was identified at 3436 cm⁻¹, 3332 cm⁻¹, 2967 cm⁻¹ and 2796 cm⁻¹ correspond to the O–H stretching vibrations in PVA and N-H vibrations stretching in the PAni/PVA composites nanofibers textile reveal in Fig. 5. The bands appear at 1762 cm⁻¹, 1498 cm⁻¹, 1324 cm⁻¹ and 1234 cm⁻¹ occur in all the IR spectra of PVA and PAni/PVA composites nanofibers textile are due to C–H stretching and free N–H stretching vibrations and the band at 826 cm⁻¹, 783 cm⁻¹ and 642 cm⁻¹ are the derives of H, C,O stretching (Estevez, 2018). In addition, the bands from 1480 to 1280 cm⁻¹ reveal the C–O symmetric and C = O stretching vibrations. Furthermore, in the IR spectra of PVA and PAni/PVA nanofibers textile, some peaks were observed at 510 cm⁻¹ was due to vibrating stretching of C-H groups which appears in PAni and PVA particles (Wang, 2018). Furthermore, present of peaks in a range of 1400 to 800 cm⁻¹ could be attributed to the methyl group vibration and straighten that is usually present in the PAni and PVA tube which can easily signify the loss of water molecule and scission of the methyl group (Ni et al., 2010).

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Fig. 5

FTIR spectra of PVA, PAni/PVA nanofibers textile composites spinning at 10 ml, 0.3 ml/h and 10 cm tips to collector distance.

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Fig. 6

FTIR spectra of PAni/Fe₃O₄/PVA composites nanofibers spinning at 16 kV, 0.3 ml/h and 10 ml.

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To further understand the chemical bonding analysis of PAni/Fe₃O₄/PVA nanofibers composite, FTIR spectroscopy was performed to determine the molecular structure and chemical bonding of PAni/Fe₃O₄/PVA composite nanofiber materials, 10 ml 16 kV, 10 cm and 0.3 ml/h electrospinning parameters are shown in Fig. 6. However, the infrared spectra of PAni/Fe₃O₄/PVA composite nanofibers indicate that these polymers are more likely to interact with magnetic nanoparticles. The FTIR analysis of composite nanofibers shows that the absorption band stretched at 3462 cm⁻¹. There is slightly decreased and widened of the band at, 3431 cm⁻¹, 3372 cm⁻¹ and 3275 cm⁻¹ are due to vibration stretching –NH groups, sudden disappearance of peaks in PAni/Fe₃O₄/PVA nanofibers composites containing 25 wt% Fe₃O₄ nanoparticles in textile materials clearly shows higher interaction of nanoparticles with nitrogen, hydrogen, carbon and oxygen atoms in the PAni and PVA chains (Wang, 2018; Ni et al., 2010).

Furthermore, due to the bond formation of the Fe₃O₄ nanoparticles with the O and H atoms and the disappearance of the bond, the decrease in the strength and width of the bond at 1672 cm⁻¹ , 1634 cm⁻¹ , 1521 cm⁻¹ indicates the decoupling between the OH and N-H bonds, in the PAni/Fe₃O₄/PVA nanofibers composite textile samples containing 15 and 20 wt% Fe₃O₄ nanoparticles were also observed at 1483 cm⁻¹ and also showed chemical bonding of Fe₃O₄ nanoparticles to PAni and PVA chain molecules (Xu et al., 2018; Ni, 2010). The change in bond strength occurred at 1490 cm⁻¹, 14747 cm⁻¹, 1062 cm⁻¹, 1031 cm⁻¹, 893 cm⁻¹, 784 cm⁻¹ and 693 cm⁻¹ also indicating their interaction. The main PAni matrix was doped with Fe₃O₄ nanoparticles, and some peaks were observed at the lowest wave number of 510 cm⁻¹ and 571 cm⁻¹, indicating the presence of Fe₃O₄ nanoparticles in the PAni/Fe₃O₄/PVA nanofibers composite textile (Ma et al., 2017).

3.4 Microwave absorption study

In order to investigate the microwave absorption ability of PAni/Fe₃O₄/PVA nanofiber composites, MVNA was employed to reveal the microwave absorption properties of the synthesized sample using the waveguide technique. Some parameter such as reflection loss (RL), relative permeability and permittivity at a given frequency as well as thickness layer in accordance with transmission line theory was calculated using the equation summarized below.

Here f is the microwave frequency, C in (m⁻¹) is the speed of light, d in (mm) is the thickness of the absorber, $Z_0$ in (Ω) is the impedance of the air and $Z_{\mathit{in}}$ in (Ω) is the input impedance of the absorber. However, the relative complex permittivity and relative complex permeability were recorded using microwave vector network analyzer, at a certain frequency in rang of 2–13 GHz. Therefore, considering the absorber thickness as one of the major parameter (1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm and 3.0 mm) that influences the position and intensity of the microwave frequency at reflection loss (RL) as this thickness was increase with addition of Fe₃O₄ nanoparticles in the composites nanofibers sample. The X-band microwave absorption study was found to be in range of 8.2–12.4 GHz, which is quite significant for commercial and many electronic application including maritime radio navigation, weather radar, Doppler, telephone microwave relay system and TV picture transmission (Liu et al., 2015; Zhang, 2017; Mohammed, 2019; Vyas et al., 2017).

The frequency dependency of the microwave absorbing properties of PAni/Fe₃O₄/PVA nanofiber composites is shown in Fig. 7. The RL of the composites nanofiber was calculated using equation (1), 2 and 3, while the reflection loss (RL) of the composites nanofiber contain (5–25 wt%) of Fe₃O₄ nanoparticles was observed and reported accordingly. The first reflection loss (RL) was revealed on the composites nanofiber contains 10 and 25 wt% of Fe₃O₄ nanoparticles at −6.4 dB and −6.3 dB while the frequency was 4.2 GHz and 3.5 GHz for 10 and 25 wt% of Fe₃O₄ nanoparticles content respectively. The second loss of the composites nanofiber was observed at −6.38 dB and −6.6 dB while the frequency was 12.9 GHz and 12.94 GHz respectively for nanofiber composites with 5 and 20 wt% of Fe₃O₄ nanoparticles loading. Suggesting that the nanofiber composites sample contain (5 and 20 wt%) are more suitable for X-band microwave absorption materials (Park et al., 2016; Take et al., 2014), while the composites nanofiber sample contain 10 and 25 wt% of Fe₃O₄ nanoparticles are found to be within the range of S-band microwave absorbing frequency (Guo et al., 2013; Levine, 2012) that could be used for surface ship radar, weather radar, and some communication satellite (microwave device/communications, microwave oven, radio astronomy, mobile phones, wireless LAN, Zig-Bee and GPS). Compared with the conductivity results in Table 1 and Fig. 6, can observed that the composites with higher conductivities at 5 wt% nanoparticles correspond to one of the better absorbing parameters (Terrazas Reza, xxxx), this indicated that both higher and lower conductive nanofiber sample have beneficial toward improving microwave absorbing parameter of the composites nanofibers (Sulistyaningsih et al., 2015; Hariani et al., Jan 2013).

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Fig. 7

Reflection loss study for PAni/Fe₃O₄/PVA nanofiber composites with different content of Fe₃O₄ nanoparticles.

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The microwave absorption study was further carryout to investigate the relative complex permeability ( ${\mu }_r$ ) measured in (H/m), while relative complex permittivity ${(\epsilon }_r)$ in (farad m^{− 1}) in the prepared composites nanofibers using the relation below

The real permeability is denoted by ${\mu }^{\text{'}}$ and real permittivity is ${\epsilon }^{\text{'}}$ was categorise as the storage ability of electromagnetic energy, while imaginary permeability $\mu "$ is related to the magnetic loss and imaginary permittivity $\epsilon "$ is attributed to how much energy is dissipated in the absorbing medium (Bahrain et al., 2016). The curve of ${\mu }^{\text{'}}$ ; $\mu "$ , ${\epsilon }^{\text{'}}$ , and $\epsilon "$ for the PAni/Fe₃O₄/PVA nanofiberious composites at different wt% of Fe₃O₄ nanoparticles is shown in the Fig. 8. It is observed that the composites nanofibers contain 10 wt% of Fe₃O₄ nanoparticles show higher reflection coefficient values of ${\mu }^{\text{'}}$ and $\mu "$ (Fig. 8 a & b) and decrease at higher frequency 2–13 GHz, which relate to the higher conductive values of the composites nanofibers, resulted from the fact that increase in the external applied electric field causes the induction charge phase of the PAni/Fe₃O₄/PVA nanofiber composites to lag behind the external electric field which cause the electromagnetic oscillation as well as space charge polarization to increase, this results from difference in values of ${\mu }^{\text{'}}$ and $\mu "$ (Wang et al., 2014; Qiu et al., 2006; Tang, 2011). Furthermore, the ${\epsilon }^{\text{'}}$ and $\epsilon "$ values obviously varies with variation of frequency in range of 2–13 GHz (Fig. 4 c & d), lower values of ${\epsilon }^{\text{'}}$ and $\epsilon "$ at higher frequency result in the shortening of the interfacial impedance gap thereby decreasing the reflection coefficient of the prepared microwave absorbent materials (Cao et al., 2015). But when the ratio of Fe₃O₄ nanoparticles increase in the composites nanofibers (5–25 wt%) then $\epsilon "$ and $\mu "$ values exhibit positive reflection coefficient values in the whole range, it is suggesting that the total microwave radiated can be absorb by the prepared materials (Li et al., 2013). If the values of $\epsilon "$ and $\mu "$ are found to be negative, neither indicating that the magnetic energy is radiated nor absorption (Tayebi et al., 2016; Li et al., 2013), this is to say that the composites, are, mainly exhibit electrical losses (Singh, 2012; Li et al., 2013). Hence, the microwave absorption properties of an EM wave absorber material depend on the values of ${\epsilon }^{\text{'}}$ and ${\mu }^{\text{'}}$ of the materials (Farias-Mancilla et al., 2016; Li et al., 2013). Moreover, the obtained microwave absorption could be attributed to attenuation of EM wave and impedance matching. The presence of PAni phase in the nanofiber composites has lowered the H_c of the nanocomposites and also increase the dielectric properties. The conductive properties of the PAni provide the environment for improved hopping of electrons, tunnelling or free band conduction which consequently enhanced the microwave absorption properties of the nanofiber composite (Li et al., 2013). Also, the presence of residual functional groups and defects in the PAni sheets favours the absorption of microwaves (Iqbal et al., 2017). The small crystallite size of the Fe₃O₄ nanoparticles increase dipole polarization thereby enhancing the $\epsilon "$ and $\mu "$ values of the nanofiber composites, the presence of multi interfaces in the nanofiber composites also serve as polarization centres which is vital for high absorption of microwaves.

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Fig. 8

Electromagnetic parameters of PAni/Fe₃O₄/PVA nanofiber composites with different content of Fe₃O₄ nanoparticles in the range of 2–13 GHz: (a) real and (b) imaginary part of the complex permeability (c) real and (d) imaginary parts of relative permittivity.

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3.5 The electrical conductivity studies

The electrical conductivities study of composites nanofibers with different contents of Fe₃O₄ nanoparticles were study 4-point probe apparatus and the data are shown in Fig. 9. However, the electrospinning of PAni/Fe₃O₄/PVA nanofibers composites was carried out, while 10 ml syringe was loaded with the electrospinning solution and spinning parameters were set at tips of the needle to collector distance 10 cm, flow rate of 0.3 ml/h and 16 kV, the variation of viscosity was attributed to the addition of Fe₃O₄ nanoparticles in the composites solution, the change in the electrical conductivity was ascribed to the different loading of Fe₃O₄ nanoparticles in the composites nanofiber which was confirm in the Fig. 9. The modified magnetite nanoparticles were found to vary the electrical conductivity due to insulating behaviour of the Fe₃O₄ nanoparticles in the composites. The electrical conductivity of the nanofibers composites with different loading of the magnetite nanoparticles was plotted in Fig. 9. The electrical conductivity of the nanofiber composites varies over the addition of Fe₃O₄ nanoparticles. Once the composites nanofiber were implanted with Fe₃O₄ nanoparticles, the interaction of polymers matrix with nanoparticles enhance the carrier dispersal thereby increasing the resistivity of the composites. Many factors are responsible for enhancing the carrier signals this includes electrostatic charges that usually generated during electrospinning or charges created by morphological defects or even nanoparticles themselves can play a significant role (Song, 2016; Kizildag et al., 2013; Iqbal et al., 2017). Therefore, blending magnetic (Fe₃O₄) nanoparticles in the conducting polymers will enhance and stabilized the association between the component, the properties of the composites nanofibers materials was influenced by the presence of magnetic nanoparticles loaded in the nanofibers composites materials (Take et al., 2014; Kim et al., 2001).

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Fig. 9

Conductivity of 10 ml solution of PAni/Fe₃O₄ /PVA Composites nanofibers at different Fe₃O₄ nanoparticles content.

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3.6 Magnetization studies

The saturation magnetization (M_s), coercive force (H_c) and Remnant magnetization (M_r) of the Fe₃O₄ nanoparticles and nanofibers composites were investigated using vibrating sample magnetometer (VSM) and the results were tabulated in Table 1. Several hysteresis behaviours of the prepared PAni/Fe₃O₄/PVA nanofibers composites materials produced with different electrospinning parameters (16 kV, 0.3 ml/h and10 cm), under the influence of the magnetic field of −10000 HOe to 10,000 HOe shows extraordinary saturation magnetization (M_s). Furthermore, the dependence of saturation magnetization introduces in the composites nanofibers materials recorded in Table 1. It was observed that the saturation magnetization (M_s), Remnant magnetization (M_r) and coercive force (H_c) were found to be M_s = 84.8 emus/g M_r = 7.6, H_c = 61.9. The superparamagnetic performance was observed in the absence of hysteresis behaviour in the composites nanofiber materials, the saturation magnetization (M_s) of the composites nanofibers was found to increase significantly due to increase of magnetic nanoparticles content (5 wt% (5.85 emu/g) to 25 wt% (58.8 emu/g)) in the composites nanofibers and therefore shows superparamagnetic performance. It is worthwhile to note that the observed magnetization of the nanofibers composites materials is considerably lower than the values recorded for the modified Fe₃O₄ nanoparticles. However, the interaction between d-orbital of the magnetite nanoparticles and the polymer matrix is ascribed to the movement of an electron with an unpaired spin in the Fe₃O₄ nanoparticles (Qiu et al., 2006; Medeiros, 2008). In order way round, the transfer of charges carrier on the surface of PAni and magnetite nanoparticles probably cause the variation of electron density on the surface of Fe₃O₄ nanoparticles thereby hindering the magnetic ability of the composites nanofibers (Lim and Choi, 2017; Keivani et al., 2010). The inter-phase interaction within the composites nanofibers usually varies the M_s of the composites, which was found to be lower than the saturation magnetization of pure Fe₃O₄ nanoparticles. With controllable electrical, magnetic, and electromagnetic properties of the prepared nanofibers composites can potentially be used for X-band microwave absorption applications (Wang et al., 2018; Sun et al., 2014).