A study of gas-sensitive properties of cobalt-modified polyacrylonitrile films by the methods of molecular modeling and quantum chemistry

The results of a theoretical study of the gas-sensitive properties of polyacrylonitrile (PAN) modified with cobalt compounds by using the methods of molecular modeling and quantum chemistry are presented. A surface cluster of cobalt-containing PAN formed by infrared heat treatment is simulated. The most stable configuration of the cluster has been determined, in which molecules of cobalt oxide and cobalt metahydroxide are located between two layers of PAN macromolecules without interacting with each other and with PAN molecules. This explains a composite structure of cobalt-containing PAN films. Molecular modeling demonstrated that the cobalt-modified PAN cluster is selectively sensitive to the molecules of chlorine, nitrogen dioxide, and carbon monoxide.     

Synthesis and properties of thermally reduced graphene oxide/polyacrylonitrile composites

Graphene oxide (GO) was prepared from graphite using a modified Hummers method. The GO dispersed in dimethyl sulfoxide (DMSO) was incorporated into polyacrylonitrile (PAN) dissolved in DMSO to prepare composite films using a conventional solution-casting method. DSC results showed a significant decrease in the cyclization temperature of polyacrylonitrile (PAN) in the presence of GO because the functional groups of GO initiated cyclization at lower temperature by an ionic mechanism. Heat treatment in air at 250 °C for 3 h led to stabilization of PAN and a simultaneous partial reduction of GO. A significant decrease in the electrical resistivity of the GO/PAN composite films was observed because the partially reduced GO acted as a conducting filler.     

AFM analysis of the surface morphology,structure, and mechanical properties of methylcellulose mixtures with colloidal silver dispersions

The surface morphology, structure, mechanical properties, and physical transition temperatures of film compositions between methylcellulose (MC) and colloidal silver dispersions (CSDs) stabilized by poly-N-vinylpyrrolidone (PVP) are studied via atomic-force microscopy (AFM), X-ray diffraction and thermomechanical analyses, and mechanical tests. It is established that composite films exhibit the characteristic granular (nanodomain) surface morphology. When the CSD content in the compositions increases, the degree of ordering of MC macromolecules enhances, grain sizes decrease from ～75 to ～60 nm (at 3 and 20 wt % of the CSD, respectively), and the film surface relief becomes smoother. For example, the surface roughness of composite films is three times less than that of the initial MC film. In other words, owing to CSD introduction, film compositions are structurized at the nanolevel. In this case, Young’s modulus and the yield stress of composite films increase successively. High-temperature heating increases the average nanodomain size to 120–180 nm (for mixtures with 20 wt % of the CSD) and stimulates the local ordering of MC macromolecular fragments with sizes of ～3–5 nm.     

Anisotropy of the Thermal Expansion of a Polycrystalline Ni–Mn–Ga Alloy Subjected to Plastic Deformation by Forging

The formation of a sharp crystallographic texture in a Ni–Mn–Ga Heusler alloy by the multiple isothermal forging has been studied. An analysis of the thermal expansion near the martensitic transformation temperatures in the as-cast and forged states of the alloy shows that the thermomechanical treatment leads to an increase in the anisotropy of the sample geometric size changing during the phase transformation, which favors an increase in the functional characteristics of the alloy. The structural studies show that the alloy structure after multiple isothermal forging has the bimodal distribution of grain sizes. The formation of the bimodal structure by forging is assumed to make it possible to enhance the stability of the functional properties of the alloy during repeated cycles of the phase transformation.     

辐射引发和热引发聚丙烯腈纤维的自由基研究

利用电子自旋共振波谱(ESR)研究了聚丙烯腈(PAN)纤维在真空以及空气气氛下经γ射线辐射引发和热引发产生的自由基. 结果显示,室温下辐射诱导产生的自由基为烷基自由基和聚亚胺自由基,辐射产生的自由基随温度升高而衰减,150 ℃时完全消失. 热引发的自由基则依赖于温度和氧气, 当PAN纤维在空气中加热至190 ℃时,开始产生多烯自由基,而且自由基浓度随温度升高而迅速增加;在真空条件下,PAN纤维经加热只产生极少量自由基. 据此推断,热引发自由基是通过热氧化反应产生的,这类自由基位于共轭结构上,其共轭长度也随温度的升高而增加.     

Iodine swelling of polyacrylonitrile I. Effect of orientation and evidence for a three-phase structure

The swelling of polyacrylonitrile (PAN) film in aqueous I₂/KI (or I₃ ^?) solutions of different concentrations up to 2.0 molal has been investigated, using both biaxially oriented and unoriented film. The absorption curve (equilibrium absorption vs concentration) for oriented film shows three distinct steps, at concentrations of 0.25, 0.65, and 1.6 molal, leading to weight increases of the sample of approximately 250%, 2000%, and 3200%, respectively. In unoriented film, smooth progressive increases of absorption are observed in place of the first and third steps; only the second abrupt step remains. A significant difference in desorption behavior is seen in extraction experiments carried out above and below the second step. It is hypothesized that the first and third steps of swelling correspond to the penetration of two different “amorphous” phases in the polymer, which together with a crystalline phase would indicate a three-phase structure for PAN. The second step of swelling may represent a conformational transition of the molecules in the phase penetrated in the first step. The effects of iodine swelling and extraction on the dynamic mechanical spectrum of PAN were also investigated, and it seems possible to associate the swelling in the region of the first and third steps with the two peaks (or transitions) in the tan δ curve of PAN, which might be regarded as glass transitions of the two amorphous phases. An unusual behavior of sample length vs temperature was observed during the dynamic mechanical measurements in the temperature region of these two transitions. Stress-strain curves were also measured on samples containing different amounts of absorbed iodine.     

Effect of Jet Swell and Jet Stretch on the Structure of Wet-Spun Polyacrylonitrile Fiber

The jet swell effect in the wet spinning of polyacrylonitrile (PAN) fiber was studied by optical microscopy and the jet swell ratio was obtained through directly measuring the diameter of the freely extruded fibers. For reflecting the actual drawing situation of the fibers in the coagulation process, the jet stretches were then corrected from the apparent values to the true values, and their effect on the cross-sectional morphology, internal structure, and orientation of the wet-spun PAN fibers was studied by optical microscopy, scanning electron microscopy, and X-ray diffraction, respectively. The results showed that jet stretch plays an important role in eliminating the adverse effects caused by the jet swell effect and affects the fiber structure; PAN fibers of uniform denier, dense and homogenous structure, and high orientation can only be obtained at a suitable jet stretch.     

Enhanced electrochemical performance of sulfur/polyacrylonitrile composite by carbon coating for lithium/sulfur batteries

A carbon-coated sulfur/polyacrylonitrile (C@S/PAN) core-shell structured composite is successfully prepared via a novel solution processing method. The sulfur/polyacrylonitrile (S/PAN) core particle has a diameter of ~ 100 nm, whereas the carbon shell is about 2 nm thick. The as-prepared C@S/PAN composite shows outstanding electrochemical performance in lithium/sulfur (Li/S) batteries delivering a high initial discharge capacity of 1416 mAh g^?1. Furthermore, it exhibits ~ 89% retention of the initial reversible capacity over 200 cycles at a constant current rate of 0.1 C. The improved performance contributed by the unique composition and the core-shell structure, wherein carbon matrix can also withstand the volume change of sulfur during the process of charging and discharging as well as provide channels for electron transport. In addition, polyacrylonitrile (PAN) matrix suppresses the shuttle effect by the covalent bonding between sulfur (S) and carbon (C) in the PAN matrix.

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Graphical abstract Cycling performance of the S/PAN and C@S/PAN electrodes and TEM image of the C@S/PAN composite.

     

Ionic conductivity study on electron beam irradiated polyacrylonitrileben polyethylene oxide gel

Different mass percent polyacrylonitrile (PAN)—polyethylene oxide (PEO) gels were prepared and irradiated by an electron beam (EB) with energy of 1.0 MeV to the dose ranging from 13 kGy to 260 kGy. The gels were analysed by using Fourier transform infrared spectrum, gel fraction and ionic conductivity (IC) measurement. The results show that the gel is crosslinked by EB irradiation, the crosslinking degree rises with the increasing EB irradiation dose (ID) and the mass percents of both PAN and PEO contribute a lot to the crosslinking; in addition, EB irradiation can promote the IC of PAN—PEO gels. There exists an optimum irradiation dose, at which the IC can increase dramatically. The IC changes of the PAN—PEO gels along with ID are divided into three regions: IC rapidly increasing region, IC decreasing region and IC balanced region. The cause of the change can be ascribed to two aspects, gel capturing electron degree and crosslinking degree. By comparing the IC—ID curves of different mass percents of PAN and PEO in gel, we found that PAN plays a more important role for gel IC promotion than PEO, since addition of PAN in gel causes the IC—ID curve sharper, while addition of PEO in gel causes the curve milder.     

YGdBCO/YBCO+BaHfO3 复合超导层的制备

采用脉冲激光沉积和化学溶液沉积相结合制备超导薄膜. 在物理法制备的 YGdBCO 薄膜上实现化学法YBCO+BHO 的同质外延生长. 利用 X 射线衍射和扫描电镜对复合薄膜的相组成、 织构和形貌进行了表征. 结果表明, 采用化学溶液沉积可以在 YGdBCO 层上制备出高性能的 YBCO+BHO 薄膜. 复合薄膜具有良好表面形貌和锐利织构, 而且复合薄膜在77 K、1 T 的磁场下J c 为0.3 MA/cm2 , 最大钉扎力达到3 GN/m3 .     

Structures and properties of the polyacrylonitrile fabric coated with ZnO-Ag composites

The polyacrylonitrile (PAN) fabric coated with ZnO-Ag composite was achieved by hydrothermal synthesis techniques and photochemical method. The PAN fabrics coated with ZnO-Ag composite were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR), UV-vis spectrophotometer and fabric induced static tester, respectively. The SEM images revealed the formation of the coating aggregates on the fiber surface. The FT-IR spectra and XRD patterns revealed the chemical structures of the coatings on the PAN fabrics. The results of UV-vis test showed that there was an obvious increase in ultraviolet resistant properties after coating. The antistatic properties results revealed the improvement in the antistatic performance of coated fabrics, attributed to the superior electrical and optical properties of ZnO and Ag.     

静电纺丝法制备聚丙烯腈/银纳米粒子复合纳米纤维及其SERS特性

利用静电纺丝技术制备了一种聚丙烯腈/银纳米粒子复合纳米纤维的表面增强拉曼光谱基底。通过调节聚丙烯腈溶液的浓度可得到不同直径、不同厚度的纤维薄膜,将聚丙烯腈的N,N-二甲基甲酰胺溶液与硝酸银溶液混合得到聚丙烯腈/Ag种子溶液,然后利用静电纺丝技术制备聚丙烯腈/Ag种子/AgNO₃复合纳米纤维;加入AgNO₃并利用水合肼二次还原后可制备适合拉曼检测的聚丙烯腈/Ag纳米粒子复合纤维膜,聚合物纤维表面和内部的金属纳米粒子的密度可调节。通过调节不同的纳米粒子的密集程度,可构筑出具有较高的电磁场增强效果的特殊的“热”结构(高局域强电磁场的亚波长区域)。而聚合物纤维内部的银纳米粒子可通过溶胀作用吸附更多的探针分子,提高拉曼检测的灵敏度。该基底有很好的SERS信号,并且可大规模制备。     

聚丙烯腈七单元组空间立构性的高分辨13C NMR表征

通过调整溶液浓度和测试温度等测试参数,与文献[1]比较我们获得了无规聚丙烯腈(PAN)和部分全同PAN样品更高分辨率的¹³C核磁共振谱. 合理归属了次甲基碳的五单元组（mmmm、mmmr和rmmr）、腈基碳与次甲基碳的七单元组（mmmmmm、mmmmmr和rmmmmr）各特征峰. 无规PAN样品服从伯努利统计模型. 一级马尔科夫和二级马尔科夫统计模型分别被用于定量计算部分全同PAN样品的五单元组和七单元组的立构分布. 计算了不同立构规整度样品的“全同单元段”和“间同单元段”平均长度, 从另一方面证实了上述的七单元组归属的正确性.     

Surface and interfacial morphologies of PAN-CVI carbon–carbon composite

Scanning electron microscopy (SEM), polarized light microscopy (PLM), and transmission electron microscopy (TEM) techniques have been used to characterize the normal surface and flank surface microstructure of a polyacrylonitrile (PAN)-based carbon fiber reinforced chemical vapor infiltrated (CVI) matrix carbon–carbon composite. Optical and SEM results indicate that the CVI deposit consists of two structures: an isotropic phase is present in the fiber bundle-bundle junctions and a second highly oriented lamellar structure is present in the intrabundle matrix. TEM shows that matrix platelets are highly parallel to the fiber axis and the crystallites of the matrix near the fiber surface exhibit better alignment than those farther away from fibers.     

Artificial solid electrolyte interphase based on polyacrylonitrile for homogenous and dendrite-free deposition of lithium metal

High chemical reactivity, large volume changes, and uncontrollable lithium dendrite growth have always been the key problems of lithium metal anodes.Coating has been demonstrated as an effective strategy to protect the lithium metal.In this work, the effects of polyacrylonitrile(PAN)-based coatings on electrodeposited lithium have been studied.Our results show that a PAN coating layer provides uniform and dendrite-free lithium deposition as well as better cycling performance with carbonate electrolyte.Notably, heat treatment of the PAN coating layer promotes the formation of larger deposit particle size and higher coulombic efficiency(85%).The compact coating layer of heat-treated PAN with a large Young modulus(82.7 GPa) may provide stable protection for the active lithium.Improved homogeneity of morphology and mechanical properties of heat-treated PAN contribute to the larger deposit particles.This work provides new feasibility to optimize the polymer coating through rational modification of polymers.     

Influence of the electronic distribution of polymers in the spatial conformation of polymer grafted carbon nanotube composites

In this work we report the covalent functionalization of multiwalled carbon nanotubes (MWCNTs) with polyacrylonitrile (PAN) and polyvinylpyridine (PVP) by the graft from method. Differences in the electronic distribution of both polymers resulted in different interaction between polymers and the nanotubes. It was found that PVP chains wrapped the nanotubes while nanotubes functionalized with PAN presented PAN chains forming amorphous entanglements on the nanoscale linked to the MWCNTs. Differences in the conformation between both polymers and the MWCNTs can be attributed to interactions between the aromatic groups in PVP and the MWCNTs through π–π stacking. The absence of aromatic groups in the case of the PAN chains favours the interaction between them. The functionalization efficiency was characterized using Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and UV–vis spectroscopy, while morphological changes were characterized by high resolution transmission electron microscopy.     

Nanocrystalline CoSn2-carbon composite electrode prepared by using sonochemistry

A sonochemical method has been used to prepare negative electrode materials containing intermetallic nanoparticles and polyacrylonitrile (PAN). The ultrasound irradiation is applied to achieve small particle size. After annealing at 490 °C under Ar-flow, the polymer PAN is partially carbonized and the metallic nanoparticles are surrounded by a carbonaceous matrix. The main metallic phase is CoSn₂. The carbonaceous coating and the surface oxides have been explored by using XPS. The resulting CoSn₂-carbonaceous phase electrode (CoSn₂@C) shows improved electrochemical behavior (ca. 450 mAh/g after 50 cycles) in comparison with previous reports on pure crystalline CoSn₂. The reaction between CoSn₂@C and Li has been studied by using XRD and ¹¹⁹Sn Mössbauer spectroscopy. The formation of large grains of crystalline Li_xSn phases after the first discharge is discarded. The small particle size which is achieved by using ultrasonication and the carbonaceous matrix contribute to maintain the Co-Sn interactions during the electrochemical cycling. The aggregation of the nanosized metallic particles upon electrochemical cycling can be suppressed by the carbonaceous matrix (pyrolytic PAN).     

A novel composite anode for LIB prepared via template-like-directed electrodepositing Cu–Sn alloy process

A novel composite anode material consisted of electrodeposited Cu–Sn alloy dispersing in a conductive micro-porous carbon membrane coated on Cu current collector was investigated. The composite material was prepared by template-like-directed electrodepositing Cu–Sn alloy process and then annealing. The template-like microporous membrane electrode was obtained as follows: (1) casting a polyacrylonitrile (PAN) solution on a copper foil, (2) then immersing the copper foil into deionized water for phase inversion, and (3) drying the membrane electrode. This method provided the composite material with high decentralization of Cu–Sn alloy and supporting medium function of conductive carbon membrane deriving from pyrolysis of PAN. SEM, XRD, and EDS analysis confirmed this structure. The characteristic structure was beneficial to inhibit the aggregation among Cu–Sn microparticles, to relax the volume expansion during cycling, and to improve the cycle ability of electrode. The reversible charge/discharge capacity of the composite material remained more than 426.6 and 445.1 mAh g⁻¹, respectively, after 70 cycles, while that of the electrode prepared by electrodepositing Cu–Sn on a bare Cu foil decreased seriously to only 11.3 mAh g⁻¹. These results show that the novel preparing anode process for LIB is a promising method and can achieve composite materials with larger specific capacity and long cycle life.     

Morphology of a silver/polyacrylonitrile nanocomposite

Silver/polyacrylonitrile (Ag/PAN) nanocomposites are synthesized at the stage of simultaneous acrylonitrile polymerization and the reduction of silver ions from a mixture of silver nitrate AgNO₃, acrylonitrile, and a photoinitiator. The synthesized films are transparent in the visible region and are characterized by a uniform dispersion of silver nanoparticles in a PAN matrix without any macroscopic agglomeration. The effects of the metal salt and photoinitiator concentrations on the size and density of metal nanoparticles in a composite are revealed.     

碳纳米管掺杂聚丙烯腈/铜室温环化为石墨的拉曼光谱分析及形成机制研究

石墨质碳质材料因具有良好的电学、力学、热学性能而在电子设备,复合材料,电池,传感器中得到广泛应用,但针对生产能耗高,污染大,成本高,不可控等现状是急需解决的核心问题。因此,通过使用较简单和成本低的制造技术在纳米级器件中获得石墨碳结构的方法是一个有吸引力的探索领域。表面等离激元技术因具有环境友好、能耗低等优点而受到广泛关注,利用等离激元技术诱导大分子链状聚合物石墨化就是一种具有广阔前景的制备技术,而Cu作为贱金属具有产量高,价格便宜等优势。基于表面等离激元技术,利用激光辐射粗糙Cu表面上的聚丙烯腈(PAN)+碳纳米管(CNT),而使聚丙烯腈在金属表面被石墨化。通过改变基底刻蚀时间、退火温度、退火时间、激光强度系统地研究了PAN/Cu和PAN+CNT/Cu得到最佳石墨化条件。实验结果表明：以PAN作为探针分子,在2.5 mol·L^-1硝酸刻蚀15min的铜基底上,观察到了增强因子为1.39×10⁴的表面增强拉曼散射(SERS)效应。通过使用拉曼激光作为光源,在退火温度为140℃时,可以观察到石墨化的PAN分子结构缺陷较少,碳氮三键消失,其I