Co-reporter:Guobin Xue, Jiang Zhong, Yongliang Cheng, Bo Wang
Electrochimica Acta 2016 Volume 215() pp:29-35
Publication Date(Web):10 October 2016
DOI:10.1016/j.electacta.2016.08.063
Cross-linked carbon nanofiber (CLCNF) was successfully prepared by directly carbonizing electrospun polyacrylonitrile (PAN) nanofiber. Comparing to non-cross-linked carbon nanofiber (NCLCNF) obtained via carbonizing of pre-oxidation PAN nanofiber, CLCNF shows better conductivity owing to its cross-linked structure. Then CLCNF was used as scaffold to support polyaniline (PANi) nanorods for supercapacitor electrode material. The hierarchical CLCNF/PANi composite displays a capacity of 206C g−1 at 0.5 A g−1 with excellent rate capability (remains 49% even at 800 A g−1), which is much higher than that of NCLCNF/PANi composite (17%). More interestingly, supercapacitor device based on CLCNF/PANi composite achieves 75.3% capacity retention after 10000 charge-discharge cycles at 10 A g−1, suggesting excellent cycle stability. All these experimental results indicate that this method for fabricating CLCNF is a substantial advancement towards the practical applications of carbon nanofiber in energy conversion and storage field.
Co-reporter:Jiang Zhong, Shu Gao, Guobin Xue, and Bo Wang
Macromolecules 2015 Volume 48(Issue 5) pp:1592-1597
Publication Date(Web):February 13, 2015
DOI:10.1021/ma502449k
Polypyrrole (PPy)/graphene oxide (GO) nanosheet composites with different GO content have been successfully prepared. The morphology, microstructure, defect property and conducting mechanism were examined by Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), field-emission scanning electron microscope (FE-SEM), X-ray photoelectron spectra (XPS), positron annihilation technology (PAT), and electrical conductivity measurements for PPy/GO conducting nanocomposites, respectively. Experimental results indicated that PPy was deposited onto the GO surface homogeneously. Four orders of magnitude increase in electrical conductivity was successfully achieved with small quantities of GO compared to pristine PPy. In order to elucidate the conducting mechanism, an electron transfer model was used to describe bipolaronic formation, which can be confirmed by XPS and positron annihilation parameters measured including positron annihilation lifetimes, positron annihilation Doppler broadening spectroscopy (DBS) and continuous distribution of positron lifetime. Electronic conductivity enhancement can be attributed to (a) the interfacial interaction between the GO layers and PPy results in the electron transfer, which leads to the increase of bipolaronic concentration, and (b) the π–π stacking between the GO layers and PPy can improve the conjugation degree of the PPy chains and the longer conjugation length makes the conducting particle delocalization more easily, leading to the increase in electron mobility. On the other hand, the continuous conducting network structure of graphene nanosheets homogeneously dispersed in the PPy matrix and carriers between localized states formed at the graphene–PPy interfaces where hopping occurred, also result in increase of conductivity.
Co-reporter:XiaoLi Yan, ZhenLi Gong, Jing Gong, Shu Gao, Bo Wang, XueFeng Ruan
Polymer 2013 Volume 54(Issue 2) pp:798-804
Publication Date(Web):24 January 2013
DOI:10.1016/j.polymer.2012.12.004
The influences of free volume and temperature on the viscoelastic properties of polycarbonate (PC)/multi-walled carbon nanotube (MWNT) composites were investigated by positron annihilation lifetime spectroscopy (PALS) and dynamic mechanical analysis (DMA). Three methods, including PALS, DMA and differential scanning calorimetry were used to determine the glass transition temperature (Tg) of PC/MWNT composites. The experimental results indicated that the higher the MWNT contents, the lower the Tg, which attributes to the large free volume hole and the enhanced polymer mobility in PC/MWNT composites with higher MWNT contents. The effect of MWNTs on viscoelastic property has been investigated in detail. A direct linear relationship between fractional free volume and viscoelastic property has been obtained using the Williams–Landel–Ferry equation based on free volume theory, which indicates that the free volume plays an important role in determining the viscoelastic property.
Co-reporter:XiaoLi Yan, ZhenLi Gong, Jing Gong, Shu Gao, Zhongliang Zhang, Bo Wang
Carbon 2012 Volume 50(Issue 8) pp:2899-2907
Publication Date(Web):July 2012
DOI:10.1016/j.carbon.2012.02.059
The microstructure, rheological and conductive properties of multi-walled carbon nanotube (MWCNT)/polycarbonate (PC) composites were investigated by positron annihilation lifetime spectroscopy, positron annihilation coincidence Doppler broadening (CDB), oscillatory rheometry and electrical resistivity for different MWCNT contents. A 10 orders of magnitude increase in electrical conductivity was achieved with very small quantities of MWCNTs. CDB was used to determine a percolation threshold value, which was in good agreement with the electrical conductivity and rheological measurements. The results showed that with increasing MWCNT content, the composites underwent a phase transition from insulating to conducting at room temperature, which was attributed to the formation of a MWCNT network. The effect of MMCNTs on the microstructure of MWCNT/PC composites has been studied by positron annihilation lifetime measurements. The results showed that the fractional free volume decreased because of the MWCNTs and the formation of conductive network. The effects of MWCNT filler on the atomic scale free volume and mechanical property of MWCNT/PC composites were also discussed.
Co-reporter:Zhenli Gong;Xiaoli Yan;Jing Gong;Junjun Wang
Journal of Applied Polymer Science 2012 Volume 125( Issue 5) pp:4028-4033
Publication Date(Web):
DOI:10.1002/app.36706
Abstract
Microstructure and damping characteristics were investigated for polycarbonate/multiwalled carbon nanotube (PC/MWCNT) composites. Dynamic mechanical analysis results show that the damping factor and the value of the energy loss fraction w are significantly increased. Especially, nearly 300% improvement in damping factor is observed in the temperature range from 140 to 150°C. Positron annihilation lifetime measurements indicate that both the o-Ps lifetime and the free volume increase with increasing MWCNT content, leading to decrease in the glass transition temperature and increase in the damping properties. The relationships among the damping, mechanical property, and the free volume have been first observed, that is, the increase of the free volume brings about a reduction in tensile strength and an increase in damping. The interfacial friction slipping of MWCNTs and the free volume play an important role in determining the damping property of PC/MWCNT composites. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012
Co-reporter:Jing Gong;Wei Gong;Zhenli Gong;Shu Gao
Polymer Engineering & Science 2012 Volume 52( Issue 8) pp:1701-1707
Publication Date(Web):
DOI:10.1002/pen.23127
Abstract
The effects of organophilic rectorite (OREC) content and interfacial interaction on the nanoscale free volume, the crystallinity, and the heat distortion temperature (HDT) have been studied for nylon 6/layered nanocomposites by positron annihilation lifetime spectroscopy (PALS) and dynamic mechanical analysis (DMA) etc. Experimental results indicated that both HDT and crystallinity increase with filled OREC due to the nucleating or epitaxial effect of nanoparticles filled and interfacial interaction between the OREC and matrix. A continuous positron lifetime analysis program based on maximum entropy lifetime method (MELT) was used to obtain the free volume distribution, which revealed the existences of two long-lived lifetime components (τ3 and τ4) corresponding to two kinds of different free volumes. We introduced a new parameter A defined as A = Aτ3/A (τ3 + τ4) and found a direct linearly relationship between the A and the crystallinity, which suggested that τ3 is mainly attributed to ortho-positronium pick-off annihilation in the interstitial free volume of the crystalline region. Experimental results also found that the interfacial interaction has different effect on the free volume properties in the different temperature range, which can be explained by a model that describes the evolution of the interfacial interaction area with temperature. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers
Co-reporter:Zhenli Gong ; Jing Gong ; Xiaoli Yan ; Shu Gao
The Journal of Physical Chemistry C 2011 Volume 115(Issue 38) pp:18468-18472
Publication Date(Web):August 16, 2011
DOI:10.1021/jp205354e
The effects of temperature and strain on the free volume and damping properties of polycarbonate/multiwalled carbon nanotube (PC/MWCNT) composites were investigated by positron annihilation lifetime spectroscopy and dynamic mechanical thermal analysis. The damping dependence on temperature indicated that the damping factors remain at a low constant value in the polymer glassy state and increase rapidly in the glass-transition area. During the glass-transition area, a direct linear relationship between the fractional free volume and the damping has been obtained using the Williams–Landel–Ferry equation based on the free volume theory, which indicates that the free volume plays an important role in determining the damping property. The strain–damping experiments reveal that a high damping factor is still obtained. A “stick–slip” model has been used to analyze the damping dependence on strain for PC/MWCNT composites, which reveals a damping mechanism of interfacial slip between the MWCNTs and the matrix.
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