Co-reporter:Xiuchao Yao, Xuechen Kou, Jun Qiu
Carbon 2016 Volume 107() pp:261-267
Publication Date(Web):October 2016
DOI:10.1016/j.carbon.2016.05.055
Intrinsic double negative metamaterials have been found in metal particles/ceramic composites, but polymer composites haven’t achieved negative permittivity and negative permeability simultaneously until now. Negative permittivity and negative permeability appear simultaneously in multi-walled carbon nanotubes (MWCNTs)/polyaniline (PANI) composites in present study. No significant change in chemical bond and crystallization is found in MWCNTs/PANI composites through ATR and XRD tests. It is found from SEM analysis that MWCNTs/PANI composites form different morphology with the increase of MWCNT content. Occurrence of negative permittivity and permeability in MWCNTs/PANI composites derives for conductive network, closed circuit structure of MWCNTs and MWCNTs/PANI composite particles. The double negative property appears in the frequency range 955–1000 MHz in 40 wt% MWCNTs/PANI composites, 930–1000 MHz in 50 wt% MWCNTs/PANI composites, 925–1000 MHz in 60 wt% MWCNTs/PANI composites and 915–1000 MHz in 70 wt% MWCNTs/PANI composites. This study makes the properties of metamaterials no longer only depend on specific combination of structures, thus possesses great significance on research and development of metamaterials.
Co-reporter:Jun Qiu, Xiangyi Wu, Tingting Qiu
Ceramics International 2016 Volume 42(Issue 4) pp:5278-5285
Publication Date(Web):March 2016
DOI:10.1016/j.ceramint.2015.12.056
Activated hollow carbon fibers (ACHFs) decorated with carbon nanotubes (CNTs) and nickel nanoparticles (CNTs–Ni–ACHFs) were prepared by thermal reduction and chemical vapor deposition technique. Microwave reflection loss, permittivity and permeability of CNTs–Ni–ACHFs composites as novel electromagnetic wave absorbents were studied in the frequency range of 2–18 GHz. It was demonstrated that CNTs–Ni–ACHFs absorbents possessed the best microwave absorbing performances whose minimum reflection loss was −43.457 dB at 13.10 GHz with a thickness of 2.0 mm, which is much better than those of Ni–ACHFs and ACHFs samples. The dielectric polarizations and magnetic loss derived from the effect of the porous structures, Ni nanoparticles, and defects in the CNTs–Ni–ACHFs composites are playing an important role for the excellent microwave absorbing performances.
Co-reporter:Xiuchao Yao, Xuechen Kou, Jun Qiu and Mark Moloney
RSC Advances 2016 vol. 6(Issue 42) pp:35378-35386
Publication Date(Web):05 Apr 2016
DOI:10.1039/C6RA03956A
Conductive polymers filled with carbon nanotubes have been proved to have negative permittivity but the mechanism of its strange properties has not been intensively studied. Thus we need to study the mechanism of negative permittivity of conductive polymer metamaterials and reveal the relationship between the permittivity and fillers. Polyaniline (PANI) filled with multi-walled carbon nanotubes (MWCNTs) is chosen as the target to explore the generation mechanism of the negative dielectric properties. PANI with low resistivity (CPA0) and MWCNTs/CPA0 composites synthesized are found to possess negative permittivity. A structure model of “double nano wires” is initially constructed after some structure and properties analysis, and the amplification mechanism of MWCNTs on negative permittivity of CPA0 and the transition phenomenon of permittivity from negative to positive value are correlated with this model. In order to verify the model, PANI with high resistivity (CHK0) and MWCNTs/CHK0 composites are prepared. The surface of MWCNTs is then coated with polyvinylpyrrolidone (PVP). These results further demonstrate the validity of the structure model of “double nano wires” to account for the negative permittivity of MWCNTs/PANI composites. This study provides an experimental basis on further exploration of metamaterials of carbon nanotube/conductive polymer composites.
Co-reporter:Xuechen Kou, Xiuchao Yao, Jun Qiu
Organic Electronics 2016 Volume 38() pp:42-47
Publication Date(Web):November 2016
DOI:10.1016/j.orgel.2016.07.029
•Negative permittivity and negative permeability appeared in multi-walled carbon nanotubes/polypyrrole nanocomposites.•The negative permittivity behavior stems from the plasma oscillation of delocalized electrons.•The negative permeability is attributed to the diamagnetic response of ring currents in the plentiful conductive loops.Multi-walled carbon nanotubes(MWCNTs)/polypyrrole(PPy) nanocomposite particles were synthesized by in-situ polymerization. Negative permittivity and negative permeability appeared simultaneously in MWCNTs/PPy nanocomposites with different content of MWCNTs. It was found from SEM analysis that MWCNTs/PPy nanocomposite particles were randomly packed with a large number of micropores, and formed a lot of conductive loops around the micropores, some MWCNTs could be cross the micropores and increase the number of conductive loops. In the meantime, MWCNTs themselves in MWCNTs/PPy composite also formed many conductive networks. The negative permittivity behavior stem from the plasma oscillation of delocalized electrons in the conductive networks, and the negative permeability was attributed to the diamagnetic response of ring currents in the plentiful conductive loops. This study should initially find a double negative metamaterial in polymer composites.Double negative property of MWCNTs/PPy nanocomposites in a wide frequency band.
Co-reporter:Xiuchao Yao, Xuechen Kou, Jun Qiu
Organic Electronics 2016 Volume 38() pp:55-60
Publication Date(Web):November 2016
DOI:10.1016/j.orgel.2016.07.033
•MWCNTs-COOH/PANI composites with 1 wt% MWCNTs-COOH had the largest negative permittivity ever reported.•The results derive from different dispersion state of MWCNTs-COOH in PANI through XRD and SEM analysis.•The present study would be beneficial to expand the application range of negative permittivity materials.Acidified multi-wall carbon nanotubes (MWCNTs-COOH) have been synthesized using mixed acid acidification, and then acidified multi-wall carbon nanotubes (MWCNTs-COOH)/polyaniline (PANI) composites with negative permittivity have been successfully synthesized by in situ polymerization. At the same time, the effects of composition and structure on the permittivity of MWCNTs-COOH/PANI composites have been systematically studied. The effects of MWCNTs-COOH content on the generation and variation of negative permittivity are illuminated by the structure model of “nano wires”. XRD analysis indicates that MWCNTs-COOH becomes the crystal nucleus and affects the crystallinity of the MWCNTs-COOH/PANI composites. SEM results indicate that different contents of MWCNTs-COOH cause various dispersion states of MWCNTs-COOH, thus lead to different morphologies of MWCNTs-COOH/PANI composites and variation of permittivity.Negative permittivity of MWCNTs-COOH/PANI composites.Download high-res image (226KB)Download full-size image
Co-reporter:Xiuchao Yao, Xuechen Kou, Jun Qiu
Organic Electronics 2016 Volume 39() pp:133-137
Publication Date(Web):December 2016
DOI:10.1016/j.orgel.2016.09.027
•Nano-Al2O3/PANI composites had negative permittivity, which was higher than that of PANI and micron-Al2O3/PANI composites.•Nano-Al2O3/PANI composite with 5 wt% nano-Al2O3 has the largest negative permittivity.•The present study would be beneficial to expand the application range of negative permittivity materials.Polyaniline (PANI) composites filled with ferroferric oxide and barium titanate were discovered to have metamaterial characteristics in recent years. In this paper, based on micron-Al2O3/PANI composites with negative permittivity, the dielectric properties of nano-Al2O3/PANI composites were studied. Nano-Al2O3/PANI composites had negative permittivity, which was considerably higher than that of PANI and micron-Al2O3/PANI composites. The higher negative permittivity was caused by the better dispersibility of nano-Al2O3, resulting in the enlargement of polarization voltage on a greater range of PANI molecular chain. Moreover, nano-Al2O3/PANI composite with 5 wt% nano-Al2O3 has the largest negative permittivity (−2.24 × 106) that has not been reported so far in oxide/PANI composites.Negative permittivity of nano-Al2O3/PANI composites.
Co-reporter:Xiuchao Yao
The Journal of Physical Chemistry C 2016 Volume 120(Issue 9) pp:4937-4944
Publication Date(Web):February 12, 2016
DOI:10.1021/acs.jpcc.5b12352
Inorganic particles/polyaniline (PANI) composite materials showed negative permittivity in recent years so that different conductive polymers filled with a wide variety of inorganic particles have been investigated for higher negative permittivity. However, the generation mechanism on negative dielectric properties of these inorganic particles/conductive polymers was still controversial. For this target, the generation mechanism of the negative dielectric properties of the metal oxide/PANI composite was studied in present study. Both PANI and Al2O3/PANI composites synthesized were found possessing negative permittivity. On the basis of structural analysis, the structure model of “crystal-nanowire” was constructed to explain the generation mechanism of negative permittivity of Al2O3/PANI composites. For further verifying the structure model, a variety of metal oxides were selected to prepare metal oxide/PANI composite materials. Negative dielectric effects were also found, proving the universality of this structure model to understand the generation mechanism of negative permittivity of Al2O3/PANI composites.
Co-reporter:Jun Qiu, Tingting Qiu
Carbon 2015 Volume 81() pp:20-28
Publication Date(Web):January 2015
DOI:10.1016/j.carbon.2014.09.011
Absorbents with “tree-like” structures, which were composed of hollow porous carbon fibers (HPCFs) acting as “trunk” structures, carbon nanotubes (CNTs) as “branch” structures and magnetite (Fe3O4) nanoparticles playing the role of “fruit” structures were prepared by chemical vapor deposition technique and chemical reaction. Microwave reflection loss, permittivity and permeability of Fe3O4–CNTs–HPCFs composites were investigated in the frequency range of 2–18 GHz. It was proven that prepared absorbents possessed the excellent electromagnetic wave absorbing performances. The bandwidth with a reflection loss less than −15 dB covers a wide frequency range from 10.2 to 18 GHz with the thickness of 1.5–3.0 mm, and the minimum reflection loss is −50.9 dB at 14.03 GHz with a 2.5 mm thick sample layer. Microwave absorbing mechanism of the Fe3O4–CNTs–HPCFs composites is concluded as dielectric polarization and the synergetic interactions exist between Fe3O4 and CNTs–HPCFs.
Co-reporter:Pincheng Xie;Yuchao Li
Journal of Applied Polymer Science 2014 Volume 131( Issue 24) pp:
Publication Date(Web):
DOI:10.1002/app.40229
ABSTRACT
Graphite nanoplatelet (GNP) was modified by polyvinylpyrrolidone (PVP), Cetyltrimethyl ammonium bromide (CTAB), γ-aminopropyltriethoxysilane (KH-550), and Stearic acid (SA), respectively. The polyvinylidene fluoride (PVDF)/modified GNP (m-GNP) nanocomposites were fabricated via solution mixing method. SEM, TEM, XRD, FTIR, and impendence analyzer were used to characterize the morphology, structure, and their electrical properties. Results showed that PVP and CTAB modified-GNP enables a better homogeneous dispersion of GNP in N,N-dimethylformamide (DMF) solvent than that of KH-550 and SA, which leads to a decreased conductivity in PVDF/m-GNP system. The permittivities of these nanocomposites were found to decrease with increasing frequencies. The SA modified-GNP filled PVDF nanocomposite has the largest dielectric constant and lowest dielectric loss. Such electrical behavior can be well interpreted in terms of the percolation theory. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40229.
Co-reporter:Yuxia Kong, Tingting Qiu, Jun Qiu
Applied Surface Science 2013 Volume 265() pp:352-357
Publication Date(Web):15 January 2013
DOI:10.1016/j.apsusc.2012.11.011
Abstract
The hollow activated carbon fibers (HACF) were prepared by using commercial polypropylene hollow fiber (PPHF) as the template, and phenol-formaldehyde resin (PF) as carbon precursors. Final HACF was formed through the thermal decomposition and carbonization of PF at 700 °C under the nitrogen atmosphere, and activation at 800 °C with carbon dioxide as the activating agent, consecutively. Then, carbon nanotubes (CNTs) were grown by chemical vapor deposition (CVD) techniques using the as-grown porous HACF as substrate. The growth process was achieved by pyrolyzing ethanol steam at 700 °C using nickel as catalyst. Finally, CNTs was grown successfully on the substrate, and a novel tree-like micro–nano carbonous structure CNTs/HACF was fabricated. The as-grown HACF and micro–nano CNTs/HACF were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), and thermogravimetric analysis (TG), respectively. Moreover, the formation mechanisms were also discussed.
Co-reporter:Yuxia Kong;Jie Yuan;Zongming Wang
Polymer Composites 2012 Volume 33( Issue 9) pp:1613-1619
Publication Date(Web):
DOI:10.1002/pc.22298
Abstract
The oriented carbon nanotubes (CNTs)/polylactic acid (PLA) composite fibers was prepared by the modified electrospinning technology, and characterized by Raman, X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR), and thermogravimetric (TG)/differential scanning calorimetric (DSC) analyses, respectively. Results showed that functionalized MWNTs have obvious orientation along the fiber axial in the interior of the electrospun PLA fibers, and improved the crystallization degree of PLA in the composite fibers due to the heterogeneous nucleation effect. The influences of polycaprolactone-functionalized multiwalled carbon nanotubes (MWNTs-PCL) on the performances of PLA fibers were studied. The crystallization region inside the MWNTs–PCL/PLA composite fibers was enlarged by increasing the MWNTs-PCL content. As a result, enhanced crystallization temperature was obtained. Moreover, a small amount of MWNTs-PCL (0.5%) improved the thermal stability of PLA matrix, while excess MWNTs-PCL (3.0%) induced the decrease of the thermal stability of PLA resin due to the agglomeration of MWNTs-PCL. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers
