Electromagnetic properties of Hollow PANFe3O4 composite nanofibers via Coaxial Electrospinning

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Electromagnetic properties of Hollow PANFe3O4 composite nanofibers via Coaxial Electrospinning


Electromagnetic properties of Hollow PAN/FeOcomposite 34

    nanofibers via Coaxial Electrospinning

    HE Tingting, LI Dawei, HUANG Fenglin, WEI Qufu, WANG Xiaoling

    5 (Key Laboratory of Eco-Textiles, Jiangnan University, JiangSu WuXi 214122)

    Abstract: FeOnanoparticles were fabricated by the chemical coprecipitation by using Triton X-100 34 as dispersant. Hollow Polyacronitrile (PAN)/FeOmagnetic composite nanofibers were fabricated 34

    through coaxial electrospinning and post-treatment. The effect of sheath feed rate on the formation of hollow structure was investigated and hollow structures of composite nanofibers were characterized

    10 using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). X-ray diffractometry (XRD) proved that FeOnanoparticles existed in composite nanofibers. The magnetic 34 properties and microwave-absorbing properties of composite nanofibers were characterized using

     Superconducting Quantum Interference Device (SQUID) and vector network analyzerrespectively.

    The study revealed that the magnetic properties of the composite nanofibers depended on the contents

    15 of FeOnanoparticles in the composites. The microwave absorption properties of hollow PAN/FeO 34 34

    composite nanofibers were better than that of PAN/FeOcomposite nanofibers. 34

    Keywords: Magnetic materials; coaxial electrospinning; hollow fibers; electromagnetic properties; FeO 34

    20 0 Introduction

    Microwave absorption materials have attracted a great deal of attention due to their potential applications in wireless data communication, satellite television and military facilities in recent years. Magnetite as a conventional microwave absorption material has played an important role in the development of microwave absorption materials for its high specific resistance and excellent

    [12]25 microwave absorption properties . However, the conventional microwave absorption materials,

    such as magnetic metal and ferrite, are too heavy to meet specific applications in many fields. [3]Coupling with low density substrates can solve this problem .

    A lot of research work has focused on polymer-based composites filled with magnetic

    [45]materials in micrometer-size, such as Ba-ferrite, Ni Zn-ferrite and FeO/YIG . However, these 34

    30 materials have difficulty in meeting the criterion in thin and light weight microwave absorber and exhibiting a strong reflection to over a wide frequency range. Coaxial electrospinning is a

    [6]straightforward technique to prepare polymer fibers with core-sheath or hollow structure . In a

    typical process, coaxial electrospinning uses one spinneret which consists of two capillaries coaxially positioned within one another. The effects of electrospinning parameters (for example

    35 voltage value) and solution properties such as viscosity, conductivity and surface tension, on the morphology and formation of nanofibers have been extensively studied. The flow rate of the outer and inner solution and the length of the outer and inner capillaries play a leading role in the

    [7-8]formation of the core-sheath structure . And magnetite (FeO), agglomerate easily for their 34

    magnetic and nano-size, which could affect the performance in its application. Electrospinning

    40 technique combines with FeOnanoparticles can reduce the aggregation of nanoparticles. 34

    The composites of hollow nanofibers with FeOnonoparticles not only have a lighter weight 34

    but also generate new absorbing mechanism to improve the performance of microwave absorption.

    Foundations: the Fundamental Research Funds for the Central Universities (No. JUSRP11102 and JUSRP20903); China National Natural Science Foundation (No. 51006046); the Natural Science Fundation of Jiangsu Province (No. BK2010140); the Research Fund for the Doctoral Program of Higher Education of China (No. 200802951011 and 20090093110004).

    Brief author introduction:He Tingting, (1989-), female, Founctional nanotextile.

    Correspondance author: Wei QuFu, (1964-), male, Professer, Functional nano-textile. E-mail:

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    In this study, solid and hollow PAN/FeOcomposite nanofibers with different FeOnanoparticle 34 34

    loadings were fabricated via electrospinning process and post-treatment. The morphology, 45 cross-sectional structure and crystal (phase) structure of the obtained nanocomposite were

    characterized by various techniques, including SEM, TEM, XRD. The magnetic and

    microwave-absorbing properties were studied using SQUID and vector network analyzer.

    1 Experiment

    1.1 Materials

    50 PAN (Mw?30000~50000 g/mol) was purchased from Sinopharm Chemical Reagent Co, Ltd,

    China. N, N dimethylformamide (DMF), Polyvinylpyrrolidone (PVP K-30, Mw?40000 g/mol) and

    Triton X-100 used were analytical grade and obtained from Sinopharm Chemical Reagent Co, Ltd,


    1.2 Preparation of FeOnanoparticles and Electrospinning Solution 34

    55 FeOnanoparticles were synthesized in the lab via chemical co-precipitation method. An 34

    appropriate amount of FeSO?7HO (0.3 mol/L) aqueous solution and FeCl?6HO (0.4 mol/L) 4232

    aqueous solution was mixed in a ratio of 2:1 (V/V).

    The mixture solution was put into 3 mouth flask under N. Then, with proper polyethylene 2oglycol addition, the temperature was increased to 70 C after the solution well-mixed. The black

    60 color precipitate of FeOwas obtained which was washed with deionized water and magnetic 34

    decantation until pH 7. Finally, FeOnanoparticles were obtained after vacuum drying for 24 h at 34


    The weight ratio of PAN and FeOwere set to 95:5, 92.5:7.5 and 90:10 and the 34

    concentration of electrospun solution was12wt%. Triton X-100, as surfactant, with the same 65 weight as FeO, was added into the spinning solutions. The FeOnanoparticles were first bath 3434

    sonicated in DMF for 12 h. Then, Triton X-100 was added to the solution and mixed solution was

    bath sonicated for another 9h. In the final step, an appropriate amount of PAN powders was added

    or another 12 h. to the previously prepared solution and bath sonicated f

    In the electrospinning process, 16 kV voltage power was applied to the solution contained in 70 a syringe via an alligator clip attached to the syringe needle. The solution was delivered to the

    blunt needle (the nozzle diameter was about 0.7 mm) tip via a microinfusion pump (WZ-50C2,

    Zhejiang, China) to control the solution flow rate at 0.6 mL/h. Fibers were collected on an

    electrically grounded aluminum foil, and the distance between needle tip and aluminum foil was

    16 cm. The solution was bath sonicated every 3h when electrospinning.

75 1.3 Coaxial electrospinning and post-treatment

    The shell fluid used for coaxial electrospinning was PAN/DMF solution with FeO34

    nanoparticles loading of 9.1 wt%( m:m: m=90:10:10). The core fluid used for PANFe3O4 Triton X-100

    coaxial electrospinning was PVP / DMF solution with a concentration of 30wt%.

    Coaxial electrospinning was performed with varying flow rate of the sheath solution. The 80 flow rate of the core solution was kept at 0.2 mL/h and the flow rate of the core solution varied

    from 0.3 mL/h to 0.5 mL/h. The length of the outer nozzle over the inner nozzle was adjusted to

    about 0.5 mm. The other conditions of coaxial electrospining are the same as the electrospun

    procession of solid PAN/ FeOcomposite nanofibers. 34

    The samples of core/shell nanofibers obtained from coaxial electrospinning were immersed in 85 deionized water at 40~50? for 48 h and the water was changed every 12 h. After immersion, the

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     core component PVP was removed, the nanofibers of hollow structure were formed. The hollow nanofibers were vacuum dried for 9 h at 60?. 1.4 Characterization Distribution of FeOnanoparticles in fibers was examined using transmission electron 34 microscopy (TEM, JEOL JEM-2100). The morphology of the PAN/FeOnanocomposite fibers 34 90 and the cross-sectional structure of hollow PAN/FeOnanofibers were observed using scanning 34 electron microscopy (SEM, Hitachi S-4800). To fix the hollow structure of nanofibers, the nanofibers were heat treated at 250 ? for 5 min under the heating rate of 3?/min when viewed the cross-sectional structure of nanofibers. The average fiber diameter of the electrospun nanofibers was measured by using Photoshop 7.0 software. 95

     The crystal structure of FeOnanoparticles and PAN/FeOfibers were investigated by 34 34 powder D8 Advance X-ray diffraction, Bruker AXS D8. The magnetic properties of the composite

     nanofibers at room temperature (300 K) were measured on MPMS (SQUID)-VSM. The microwave-absorbing properties of nanofibers were tested on N5230 vector network analyzer (Agilent technologies). 100

     2 Results and discussion 2.1 Microstructure of solid PAN/ FeOcomposite nanofibers 34 a b c Fig.1 TEM of “a” FeO“b” PAN/ FeO(92.5:7.5) and c PAN/ FeO(90:10) 34 34 34 105 TEM observations clearly revealed that structure of the FeOnanoparticles and the 34 dispersion of FeOnanoparticles in PAN nanofibers, as illustrated in Figure 1. The average 34 diameter of FeOnanoparticles was about 26.2 nm which corresponded to XRD result. The FeO34 34 nanoparticles appeared to scatter uniformly inside the fibers and FeOnanoparticles aggregated 34 110

     into small clusters in the fiber, as shown in Figures b and c. It was obviously observed that there were more FeOnanoparticles in the fibers as the FeOweight ratio increased. However, FeO34 34 34

     nanoparticles in Figure 1c looked less aggregated that that in Figure 1b, which might be attributed to the effect of ultrasonic dispersion and Triton X-100. FeOnanoparticles could agglomerate 34 into large aggregates easily due to high surface force and magnetic force. Ultrasonic vibration 115 [9]could destroy the coulomb force and van der waals force making large aggregates broken .

    Triton X-100 as nonionic surfactant adsorbed around FeOnanoparticles and made space 34 [10]repulsion force generated among FeOnanoparticles . Therefore, sonication and surfactant 34

    facilitated the dispersion of FeOnanoparticles in the elctrospun fibers. 34

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     120 a b c Fig.2. SEM of “a” PAN, bPAN/ FeO(95:5) and c PAN/ FeO(90:10) 34 34 The SEM images indicated that the addition of FeOnanoparticles did not change the 34

    125 morphology of the electrospun naofibers obviously, but the electrospun fibers looked finer when

     the FeOnanoparticles were added. The average fiber diameter of nanofibers with m:m 34 PANFe3O4

     =90:0, 95:5 and 90:10 were 280.2 nm227.6 nm and 192.7nm, respectively. It showing a reduce in average diameter of PAN/ FeOnanofibers with the increase of FeOmass fraction, which may 34 34

     be attributed to the change in surface tension and viscosity of the electrospinning solution.

130 2.2 Microstructure of solid PAN/ FeOcomposite nanofibers 34

     a b c Fig.3 Cross-sectional structure (SEM) of hollow PAN/ FeOnanofibers 34 (a V:V=0.3:0.2, b V:V=0.4:0.2, cV:V=0.5:0.2) shellcoreshellcore shellcore 135

     Figure 3 shows the structures of hollow PAN/FeOnanofibers after the removal of the inner 34 component PVP by immersing in deionized water. The different flow rates of core fluid and shell

     fluid significantly affect the structure of hollow PAN/FeOnanofibers, as indicated in Figure 3. 34 When V:V=0.3:0.2, some nanofibers became flat and collapsed. The main reason was the shellcore

    140 sheath flow rate was too slow in this case, therefore the sheath solution could not coat the core solution fully during electrospining. The sheath solution was the driving fluid in coaxial electrospinning, if its flow rate was too small, the core solution would not completely follow the

     sheath to rotate and move at high speed under high voltage electric field. Flat nanofibers would appear due to the asynchronous motion of core and sheath solution. When V:V=0.4:0.2, shellcore

    homogeneous hollow PAN/FeOnanofibers were obtained. When V:V=0.5:0.2, less 145 34 shellcore hollow fiber were formed and more solid fibers were obtained. If the sheath flow rate was too fast, the core flow rate was not fast enough to form the core-shell nanofibers, leading to the formation of solid nanofibers. 2.3 XRD


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    (311) FeOnanoparticles 34

     (511)(440) (220) (400) (422) Intensity (311) (220) PAN/FeO(9.1%) 34(440) (511) 20 40 60 80


     Fig.4 XRD patterns of FeOnanoparticles and PAN/ FeOcomposite nanofibers 34 34 Figure 4 shows the XRD patterns of FeOpowder synthesized and solid PAN/ FeO 34 34

    155 composite nanofibers. FeOnanoparticles showed crystalline peaks at 30.22?, 35.56?, 43.26?, 34 53.74?, 57.20 ? and 62.74?, which were assigned to (220)(311)(400)(422)(511) and (440)

     crystal planes of FeO(PDF #65-3107) respectively. The average grain size (D) was estimated 34 from the Scherrer Equation ,D=κλβcosθ (Where K was a constant taken as the normal value of

     0.89λ was 0.154 nmβ is the full width at half-maximum (FWHM), and θ was the Bragg angle).

    160 The peak at 2 θ= 35.56? was used to estimate the particle size. The calculated value was about

     25.9 nm which was close to the average diameter of FeOnanoparticles characterized by TEM, as 34 shown Figure 1. The crystalline peaks of solid PAN/ FeO(9.1%) composite nanofibers were 34 located at 30.22?, 35.56?, 57.20 ?and 62.74?. The diffraction peaks’ positions of composite nanofibers were the same as those of FeOnanoparticles, however, the intensity of the diffraction 34

    peak decreased significantly. These observations indicated that it was physical combination 165

     between FeOnanoparticles and PAN without chemical reaction. The crystal construction of 34 FeOnanoparticles in nanofibers did not change after electrospining. 34 2.4 Magnetic properties Figure 5 shows the plots of magnetization (M) versus magnetic field (H) of FeO34

    nanoparticles and PAN/FeOcomposite nanofibers. The result illustrated that the saturation 170 34 magnetization (Ms), remanent magnetization (Mr) and coercivity(Hc) values of FeO 34

     nanopartices were 76.9emu/g6.8emu/g and 51 Oe. However the corresponding values of PAN/ FeOcomposite nanofibers were 6.7emu/g, 0.44emu/g and 49 Oe. The FeOnanoparticle loading 34 34 estimated from the Ms was found to be 8.7 wt% (Ms is proportional to the amount of FeO). The 34 possible reason was that the magnetic FeOnanoparticles coated by PAN nanocomposite 175 34

    hindered the magnetic expression of FeOnanoparticles. It meant that the magnetic properties 34

    could be tailored by adjusting the amount of FeOin the nanocomposite. 34

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     80 Fe0nanoparticles 3460 PAN/Fe0(9.1%) 3440 20

    0 -20




    -15000 -10000 -5000 0 5000 10000 15000 H(Oe)

     Fig.5. Magnetic hysteresis loops of FeOnanoparticles and solid PAN/FeOcomposite nanofibers 34 34 180

     The magnetic properties of FeOparticles are affected by their size. FeOparticles with the 34 34 diameter below a critical size named DSD (Diameter of single domain) and DSPM (Diameter of

     superparamagnetism) are composed of single domain particles and exhibits superparamagnetism [11]. It has been reported that DSD value was 128 nm and DSPM value lied between 25 and 30 nm.

    In the single domain region, the Hc changes with the particle size. Since the particle size did not 185

    change in PAN/ FeOcomposite nanofibers and nanoparticles were dispersed uniformly in fibers, 34

    so the Hc remained similar to that of FeOnanoparticles. The FeOparticles synthesized showed 34 34

    ferromagnetic properties.

     2.5 Microwave-absorbing properties

     0 Solid PAN/Fe0(90:10) -5 34 Hollow PAN/Fe0(90:10) 34 -10 -15 -20 -25 (16.75,-34.2) -30 Reflection loss(dB) M(enu/g) -35 (16.79,-37.7) -40 8 10 12 14 16 18 Frequency(GHZ)

     190Fig.6. Reflection loss of solid PAN/ FeOand hollow PAN/ FeOcomposite nanofibers 34 34

     The reflection loss of PAN/FeOand hollow PAN/FeOcomposite nanofibers is presented 34 34 in Figure 6. The results revealed that the reflection loss of PAN/ FeOand hollow PAN/ FeO 34 34

     195 composite nanofibers was less than ?10 dB over the range of 8.7518GHz and 8.1-18 GHz respectively. The reflection loss of PAN/ FeOand hollow PAN/ FeOcomposite nanofibers was 34 34 less than ?20 dB over the range of 12.718GHz and 10.6-18 GHzrespectively. Additionally,

     when the reflectivity reached ?10 dB, the reflection loss of the microwave absorption materials achieved 90%. When the reflectivity was ?20 dB the reflection loss of microwave absorption

    materials achieved 99%. The reflection loss peak of PAN/ FeOcomposite nanofibers occurred at 200 34

    about 16.75 GHz and the value was 34.2dB. However the peak of hollow PAN/ FeOcomposite 34

    nanofibers occurred at about 16.79 GHz and the value was 37.1dB. The reflection loss of hollow

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     Ocomposite nanofibers was 7.7 dB lower than those of normal PAN/ FeOcomposite PAN/ Fe34 34 nanofibers at 12.6 GHZ.

    205 It was found that microwave absorption properties of hollow PAN/FeOcomposite 34 nanofibers looked better than those of PAN/ FeOnanocmposites. PAN/FeOnanofibers can be 34 34

     regarded as a type of monolayer microwave-absorbing material, but the hollow PAN/FeO34 nanofibers can be considered as multi-layer microwave-absorbing material with air trapped inside.

    When microwave enters the hollow fibers, it goes through three-Rams (Radar absorbing materials)

    210 and would be reflected more times in the hollow structure. Multi-layers can expand absorption bandwidth and enhances absorbing effect to a certain extent. Therefore, hollow structure not only

     contributes in weight but also improves the performance of microwave absorption. 3 Conclusion Hollow PAN/FeOcomposite nanofibers have been fabricated by coaxial electrospinning 34

    and post-treatment. It was found that homogeneous hollow PAN/FeOnanofibers could be 215 34 obtained after post-treatment, when V:V=0.4:0.2. XRD patterns indicated that it was physical sellcore combination between FeOnanoparticles and PAN and the crystal configuration of FeO 34 34 nanoparticles remained unchanged after electrospining. Magnetic properties of composite nanofibers could be changed by adjusting the amount of FeOin the nanocomposite. The hollow 34

    structure could improve the microwave absorption properties of composite nanofibers. The strong 220 absorption frequency bandwidth (RL <?10 dB and ?20 dB) of PAN/FeOand hollow PAN/FeO 34 34

     composite nanofibers was expanded from 9.25 to 9.90 GHz and 5.3 to 7.4 GHz, respectivelyand

     the maximum reflection loss increased from 34.2 to 37.7 dB. It is believed that hollow PAN/

     FeOcomposite nanofibers can be used as microwave absorption materials with light weight and 34

    strong microwave absorption. 225

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     同轴静电纺制备中空 PAN/FeO纳米复合纤维及电磁 34 性能研究

     何婷婷,李大伟,黄锋林,魏取福,王晓玲 ?江南大学生态纺织教育部重点实验室,江苏 无锡 214122 摘要,采用化 学共沉淀法制备纳米四氧化三铁,选用曲拉通 X-100 为分散剂,利用同轴静 电纺丝法结合260 后处理,制备中空 PAN/FeO磁性纳米复合材料。同时使用扫描电镜?SEM 和透射电镜 34 TEM?对内外液流速对中空结构的微观形貌影响进行研究和 FeO在纤维中的 分布进行观34 察。X 射线衍射仪?XRD?验证了四氧化三铁在复合纳米纤维中的存在。通过 磁性实验和 矢量网络分析仪研究了纳米复合材料的磁性和吸波性能。结果表明,纳米复合材 料并具有一 定磁性,并可由磁性颗粒的加入量进行控制,中空 PAN/FeO纳米复合材料的 吸波性能优34 于实心纳米纤维。 关键词,磁性材料(同轴静电纺(中空纤维(电磁性能(四氧化三铁 265


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