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 analyzer，respectively.
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
[1–2]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. Coupling with low density substrates can solve this problem .
A lot of research work has focused on polymer-based composites filled with magnetic
[4–5]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
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.
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 3