Accepted Manuscript

Investigation of microwave absorbing properties for magnetic nanofiber ofpolystyrene-polyvinylpyrrolidone

Seyed Hossein Hosseini, Mahsa Sadeghi

PII: S1567-1739(14)00057-1

DOI: 10.1016/j.cap.2014.02.020

Reference: CAP 3581

To appear in: Current Applied Physics

Received Date: 8 November 2013

Revised Date: 3 February 2014

Accepted Date: 22 February 2014

Please cite this article as: S.H. Hosseini, M. Sadeghi, Investigation of microwave absorbing propertiesfor magnetic nanofiber of polystyrene-polyvinylpyrrolidone, Current Applied Physics (2014), doi:10.1016/j.cap.2014.02.020.

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Investigation of microwave absorbing properties for

magnetic nanofiber of polystyrene-

polyvinylpyrrolidone

Seyed Hossein Hosseini1∗∗∗∗

, Mahsa Sadeghi2

1. Department of Chemistry, Faculty of Science, Islamshahr Branch, Islamic Azad

University, Tehran-Iran

2. Department of Chemistry, Faculty of Science and Engineering, Saveh Branch, Islamic

Azad university, Saveh, Iran

*Correspondence to: Seyed Hossein Hosseini, Department of Chemistry, Faculty of Science,

Islamshahr Branch, Islamic Azad University, Tehran-Iran; Email: shhosseini@iiau.ac.ir.

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ABSTRACT

Aligned magnetic blend of polystyrene-polyvinylpyrrolidone (PS-PVP) nanofibers

were prepared by this method. First, polystyrene-polyvinylpyrrolidone (PS-PVP)

blend solution in THF was synthesized. Then magnetic of PS-PVP-Fe3O4-

polyethylene glycol (PEG) was prepared by masking method. Finally, magnetic

nanofiber of PS-PVP-Fe3O4- PEG was prepared by electrospinning method, too.

An electric potential difference of 25 kV was applied between the collector and a

syringe tip, and the distance between the collector and the tip was 13 cm. Fe3O4 is

exhibit various magnetic properties of which the complex permeability and the

permittivity, in particular, are important in determining their high frequency

characteristics. The magnetic oxide particles and nanofiber of nanometer size were

characterized by TEM and SEM respectively. The thermal properties of nanofibers

were determined by TGA and DSC. The magnetic characterization of the fibers

was also performed by VSM and AFM techniques. On the other hand, nanofiber

with diameters ranging from 30 to 40 nm, showing at room temperature, coercive

field values of around 25 KV and saturation magnetization was 1.1 emu/g.

Microwave reflection loss of the sample was tested at 8–12 GHz microwave

frequencies and the results showed that magnetic nanofiber possessed the

microwave absorbing properties.

Keywords: Nano-structures; Polymer (textile) fiber;

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Polymer-matrix composites (PMCs); Electrical properties; Magnetic properties

1. Introduction

Many types of radar absorbing materials are commercially available and, at

present, the most cost effective means of shielding radar radiation, controlling

electromagnetic interference and dissipating electrostatic charge is to use either

magnetic or dielectric fillers [1] or intrinsically conducting polymers [2].

Magnetic absorption materials made by dispersing magnetic fillers in an insulating

matrix continue to play an important role in the investigation and application of

microwave absorption materials [3]. As ferrites can avoid the skin effect at high

frequency and make the electromagnetic wave enter effectively due to their high

resistivity, they can attenuate electromagnetic wave efficiently. In addition, for its

higher efficiency and lower cost than that of other materials, they have been

among the most popular conventional magnetic fillers. However, for a long period

of time, much attention about ferrites has been focused on researching microwave

absorption properties of new types of ferrites [4,5]. We have reported synthesis of

nanocomposites containing some of ferrites compounds and investigated their

microwave absorption properties [6,7].

Nanofibers are fibers that have diameter equal to or less than 100 nm. Considering

the potential opportunities provided by nanofibers there is an increasing interest in

nanofiber technology. Amongst the technologies including the template method

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[8], vapor grown [9], phase sepration [10] and electrospinning has attracted the

most recent interest. Electrospinning is a simple and versatile method for

generating ultrathin fibers from a rich variety of materials that include polymers,

composites and ceramics [11].

In this paper, the main object is to develop a fiber compounds with microwave

absorption properties. So we have synthesized magnetic nanofiber with

polystyrene-polyvinylpyrrolidone- Fe3O4-polyethylene glycol, PS-PVP-Fe3O4-

PEG.

2. Experimental

2.1. Material

Polystyrene (Merck chemical Co.) and polyvinylpyrrolidone (Merk chemical Co.)

and ferrous sulfate heptahydrate and poly ethylene glycol (Mw: 4000).

Tetrahydrofuran (THF, 99.5%, Duksan chemical Co.) and hydrogen proxide and

chloroform were used as solvent.

2.2. Measurement of properties

An ultrasonic reactor (Bandelin Sonorex Digitec) was used to provide the

ultrasonic field. The physical properties of nanofibers and topographic pictures of

nanofibers were studied by Atomic Force Microscopy (AFM). Transition electron

microscopy (TEM) measurements were performed using PHILIPS EM 208. One

drope of the sample solution was deposited on to a copper grid and the excess of

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the droplet was blotted off the grids with a filter paper. The sample was dried

under ambient conditions. The Nanoparticles size & morphology were observed

by TEM images. The magnetic properties of fibers and magnetic nanoparticles

were measured by a Vibrating Sample Magnetometer (VSM), The morphology of

fibers was examined by Scanning Electron Microscopy (SEM, PHILIPS XL30).

Microwave absorbing properties were measured by a Vector Network Analyzers

(Agilent Technologies Inc. 8722) in the 8–12 GHz range at room temperature.

2.3. Synthesis of Fe3O4 Nanoparticles

Fe3O4 Nanoparticles were prepared by Core-Shell system. First, 70 gr of PEG

(Mw: 4000) and 3 gr of FeSO4.7H2O were solved in 140 ml of distilled water. This

solution was transferred to a three-neck flask equipped with a condenser and

nitrogen gas inlet and outlet with vigorous stirring for 30 min. Then 20 ml of H2O2

20% was added to the solution. This reaction was performed at 50°C for 6h at pH:

13. The pH of the reaction was set with NaOH 3 M. Then the solution was

centrifuged. The Fe3O4 magnetic nanoparticles were prepared

2.4. Preparation of the blend solution

The polystyrene-polyvinylpyrrolidone (PS-PVP) blend solution was prepared. A

4:1 mole ratio of PS and PVP were dissolved in THF to a final concentration of 11

wt%. The solution was then stirred at room temperature at 1000 rpm for a period

of 7 h using a mechanical stirrer, and then filtered through a filter paper to remove

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any particulate matter. Finally, by adding Fe3O4-PEG to the filtered solution,

magnetic PS-PVP-Fe3O4-PEG solution was prepared, which was then stirred for a

period of 2 h. This solution was made using the following procedure.

2.5. Electrospinning

Electrospinning, have only 6 or 7 molecules across. The PS-PVP blend and PS-

PVP-Fe3O4-PEG nanofibers were synthesized on a aluminum electrode

(10cm×10cm). An electric potential difference of 25 kV was applied between the

collector and a syringe tip, and the distance between the collector and the tip was

13 cm. Although we tried to fabricate the same number of blend nanofibers as

composite nanofibers on the electrode, a slightly different number of both fibers

were generated and collected.

3. Results and discussion

The electrospinning process has been documented using a variety of fiber forming

polymers. By choosing a suitable polymer and solvent system, nanofibers with

diameters in the range of 40-2000 nm be made. Magnetization studies have shown

that the magnetic PS-PVP-Fe3O4-PEG nanofibers exibit superparamagnetic

behavior and shows no hysteresis. The magnetic characterization of the fibers was

performed by Vibrating Sample Magnetometer (VSM) and Atomic Force

Microscopy techniques. The magnetization curve of PS-PVP-Fe3O4-PEG

nanofibers is presented in Figure 1. An electric potential difference of 10 kV was

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applied between the collector and a syringe tip, and the distance between the

collector and the tip was 13 cm. On the other hand, nanofiber with diameters

ranging from 30 to 40 nm, showing at room temperature, coercive field values

was around 25 kV and saturation magnetization was (M r =1.1 emu/g).

In our study, the physical properties of PS-PVP-Fe3O4-PEG nanofibers were

exhibit by Atomic Force Microscopy (AFM) with different size. The dark spots

that were shown like tops are magnetic nanoparticles Fe3O4 and light area of

polymer are base and are PS-PVP nanofibers (Figure 2).

The histogram nanofibers of polystyrene and magnetic nanoparticles of Fe3O4-

PEG have been shown in Figure 3. The height of the peak shows the size of

nanoparticles that is scattered in polymeric-bed.

Figure 4 shows the size of MNPs of Fe3O4-PEG were almost 61.5 nm. The TEM

images show that size of nanoparticles Fe3O4 were about 10-50 nm.

The SEM images of PS-PVP (w/w 4:1) and PS-PVP-Fe3O4-PEG nanofibers were

shown in Figures 5 and 6. The average of diameter of nanofibers is about 100-150

nm. In the current study nanoparticle are microhollow spherical and the diameter

of each hole is about 2 to 5 micrometers.

3.1. Reflection loss

Different Fe doped Fe3O4 have the similar change for the dielectric and the

magnetic spectra which suggests that their electromagnetism loss mechanism

should be the same. Now, the electromagnetism loss mechanism of the materials

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will be explained by the characteristic change of loss factor for sample. A novel

phenomenon is discovered that the electromagnetic loss factor has suddenly a step

change at a certain frequency. Loss factor is depended to Fe value. When Fe

concentration is increased, there is a sharp increase of loss factor [12]. The energy

state of anti-ferromagnetic clusters could be linked with the content, which affects

the potential barrier height between ferromagnetic clusters and anti-ferromagnetic

clusters [13]. Besides, the microwave loss may also come from the resistive part

[14]. The lower resistivity may arouse larger dielectric losses.

In the other hands, according to transmission line theory, the reflection loss (RL)

of electromagnetic radiation, under normal wave incidence at the surface of a

single-layer material backed by a perfect conductor can be given by

(1)

where is the characteristic impedance of free space,

(2)

Zin is the input impedance at free space and materials interface:

(3)

where µr and εr are the complex permeability and permittivity of the composite

medium respectively, which can be calculated from the complex scatter

parameters, c is the light velocity, f is the frequency of the incidence

electromagnetic wave and t is the thickness of composites. The impedance

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matching condition is given by Zin = Z0 to represent the perfect absorbing

properties.

In this research, nanofiber was pasted on glass or aluminum plate with the area of

10mm×10mm as the test plate. The microwave absorbing properties of the

nanofiber with the 20 w.% Fe3O4 NPs at 1 mm nanofiber thicknesses were

investigated by using vector network analyzers in the frequency range of 8 –

12GHz. Figure 7 shows the variation of reflection loss versus frequency

determined from PS-PVP-Fe3O4- PEG. For nanofiber of PS-PVP-Fe3O4- PEG with

the coating thickness of 1 mm the reflection loss values less than -11 dB were

obtained in the frequency of 8–14 GHz. Its value of minimum reflection losses are

-11 and -8 dB at the frequencies of 10 and 12 GHz, respectively. The absorbing

bandwidth at -10 dB is 0.3 GHz.

Such suitable conductivity and magnetic transformation will be beneficial to the

materials absorbing microwave. Further studies on the relationship among the

absorbing properties, electrical conductivity and magnetic domain structures of the

compounds are in process.

4. Conclusion

Fe3O4-PEG solution was added into blend precursor solution to improve the

magnetic and morphology properties and distribution of diameter of PS-PVP-

Fe3O4-PEG nanofibers. The average of diameter of nanofibers is about 100-150

nm and microhollow spherical for nanoparticles. This nanofiber is good candidate

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for microwave absorbing materials. The value of minimum reflection loss for the

nanofiber with 20 w.% Fe3O4 NPs is approximately −11 dB with a thickness of 1

mm at the frequency of 10 GHz.

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Figure Titles:

Figure 1. Magnetization vs. applied field plot for PS-PVP-Fe3O4-PEG nanofibers

at room temperature

Figure 2. AFM images of electrospun nanofibers of PS-PVP-Fe3O4-PEG

Figure 3. Magnetic histogram of Fe3O4-PEG nanofibers at room temperature

Figure 4. TEM images of electrospun nanofibers of PS-PVP-Fe3O4-PEG

Figure 5. SEM images of PS-PVP (w/w 4:1) nanofibers

Figure 6. SEM images of electrospun nanofibers of PS-PVP-Fe3O4-PEG

Figure 7. Frequency dependence of RL for the PS-PVP-Fe3O4-PEG

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Highlights

• We report a PS-PVP-Fe3O4-PEG nanofiber with magnetic property

• PS-PVP-Fe3O4-PEG nanofiber is good candidate as microwave absorbing materials