往复射流分散与超声分散对纳米碳管在不饱和聚酯中分散效果的研究

分别采用超声分散法和本课题组研究的新技术-往复射流分散法对一系列含不等量多壁纳米碳管的前驱体混合物进行了分散,并将其固化制得了不同的复合材料.其中,前驱体混合液的粘度通过旋转粘度计测定,并使用扫描电镜观测最终所得复合材料中纳米碳管的分布状态.检测结果表明,一方面,往复射流分散工艺相对于超声分散更有利于纳米碳管在聚合物中的分散,而且碳管的分散均匀程度随工作次数的增加而有所提升.但另一方面,前驱体混合液的粘度同时亦随之大幅度下降,而这将减弱后续的前驱体固化过程的工艺性.     

力学所发明自组装制备手性可控纳米碳管新方法

<正>纳米碳管作为潜在的第三代晶体管,其手性决定其表现出的金属导体或半导体性能。然而,如何制备手性可控的纳米碳管,成为制约纳米碳管在微纳电子、集成电路等领域应用的关键问题。国外最新实验研究表明:石墨烯纳米条带在纳米碳管的辅助下,可以自组装形成螺旋结构,有趣的是部分实验中发现了自组装纳     

乳液聚合法制备纳米SiO2/PMMA复合粒子及其表征

利用可聚合乳化剂在纳米SiO2表面进行乳液聚合,成功制备出了具有核壳结构的纳米SiO2/PMMA复合粒子,并通过FTIR、TEM、XPS和TGA分析了其粒子形态和包覆效果.结果表明:偶联剂MPTMS已成功接到了改性后的纳米siO2的表面,其谱图呈现了PMMA和纳米SiO2的复合结构而没改变原来纳米SiO2结构.复合粒子的粒径约50～100 nm,形态具有外层较浅内层较深的核壳结构.XPS分析表明,SiO2被PMMA包覆后,其表面的Si含量降为1.29;,用甲苯对纳米SiO2/PMMA复合粒子抽提后,Si含量增加到3.50;.基于索氏抽提实验和TGA分析,PMMA与SiO2比(fp)、PMMA对SiO2接枝率(fr)和PMMA的有效接枝率(fe)分别为95.8;、63.4;和67.1;.     

纳米石墨和纳米碳管薄膜在低电场下的稳定场发射

采用微波等离子体化学气相沉积法(MPECVD)制备出了纳米石墨和纳米碳管混合薄膜材料.通过扫描电镜(SEM)和拉曼光谱(Raman)对薄膜材料的结构和形貌进行了分析.研究了薄膜材料的场发射性能.场发射结果显示:其开启电场为0.7 V/μm1,在较低电场下(3.7 V/μm1)即可获得5.2 mA/cm2的电流密度,此电场下发射点密度可达1.6×107 cm-2,发射点均匀,亮度稳定.迭代法计算结果表明制备的纳米石墨和纳米碳管混合薄膜材料的功函数仅为3.2 eV.这些表明该薄膜材料为优良的场发射冷阴极材料.     

梳子状ZnO纳米棒阵列的制备及表征

采用水热法在HTlc-ZnAlCO3纳米片上对称生长出平行排列的梳子状ZnO纳米棒.利用X射线衍射(XRD)、场发射扫描电子显微镜(FESEM)对得到的样品进行表征.揭示ZnO纳米棒的可控生长规律,在此基础上对其生长机理进行初步探讨.     

火焰热解法生长定向碳纳米管

本文研究了火焰热解法的碳纳米管制备实验(催化剂为Fe/Mo/Al2O3),发现在火焰热解法条件下碳纳米管阵列可在火焰热解腔中定向生长,产物较为整齐,碳管形态较好.本课题组之前在电场作用下采用Fe(CO)5为催化剂,在V型体火焰中亦可制得碳纳米管阵列,对比两者发现热解腔内制得阵列碳纳米管长度较长,定向性更优;而电场作用下的V型体火焰中制得阵列中的碳纳米管较直.进而,在火焰热解法制备中施加电场,发现随电压增加,碳纳米管阵列更直,碳管长度和产量明显增长.     

取向性二氧化硅纤维的制备及其发光性能研究

通过气相输运沉积的途径成功制备了大量定向排列的SiO2纤维.对比实验发现,取向性氧化硅纤维的生长与载气的气流量、原料的球磨处理有关.并利用XRD、SEM等方法分析表征样品,结构表明取向性纤维为无定形结构,平均直径为700 nm.在波长为260 nm的Xe灯激发下,产物的室温光致发光谱在450 nm和415 nm处分别出现两个蓝光发光峰,其将在微纳米光电器件中发挥作用.     

乙酰丙酮对PMMA负载锐钛矿型TiO2薄膜及其光催化性能影响

以钛酸丁酯作为钛源,水为溶剂,乙酰丙酮(AcAcH)为表面修饰剂,采用微波水热辅助溶胶-凝胶法制备了纳米晶二氧化钛水溶液,利用提拉镀膜法在聚合物聚甲基丙烯酸甲酯(PMMA)基板上沉积得到了透明TiO2纳米晶薄膜.通过X射线衍射(XRD)、红外光谱(FTIR)、透射电子显微镜(TEM)、原子力显微镜(AFM)和紫外-可见光吸收光谱(UV-Vis)等对TiO2纳米颗粒和薄膜的晶相组成、表面形貌及光学性能进行表征.同时通过紫外光光催化降解罗丹明B研究了TiO2薄膜的光催化性能.结果表明:通过引入乙酰丙酮,可以得到高度分散、晶相为锐钛矿型的TiO2水溶胶,在PMMA基板上沉积得到的薄膜表面平整、致密,具有良好的透光率,经过180 min紫外光照射,对罗丹明B的降解率达到90;以上.     

用AAO模板法制备高度定向碳纳米管阵列的研究进展

用二步氧化法可以在草酸或硫酸中制备多孔氧化铝（AAO）模板,这种模板成本低,高度有序,六角排列。利用化学气相沉积技术可以制备高度定向生长的碳纳米管,这将有利于研究碳纳米管的性质和它在纳米电子器件及其他领域的应用。本文介绍了AAO模板的阳极氧化工艺,成膜机理以及不同电解液,氧化电流、电压等因素对纳米孔道的影响。讨论了催化剂和气相沉积温度对碳纳米管特性的影响,并指出这种制备碳纳米管的技术需要深入研究的问题。     

氮化铝纳米结构的生长与物性研究

氮化铝(AlN)纳米结构除了具备AlN本身宽带隙、高热导率、高击穿场强和高热稳定性等优异物理性能外,还具备表面效应和小尺寸效应所引起的独特物理和化学性质,因而受到人们的广泛关注.在国内外研究学者多年的不懈努力和研究下,目前已经能够生长结晶质量较高的AlN纳米结构,并在光学、电学和磁学等领域发挥着重要的作用.在本文中,首先探讨了包括化学气相沉积法、物理气相传输法、直流电弧放电法、氢化物气相外延法、分子束外延法等不同AlN纳米结构制备方法的研究进展.随后系统地总结了在不同方法制备过程中,温度、源、气氛、生长时间和催化剂等因素对AlN纳米结构的形貌和结晶质量的影响,并分析了它们的生长机理.最后还详细介绍和讨论了AlN纳米结构的物理性质.     

烧结工艺对碳纳米管/羟基磷灰石复合材料力学性能与微观结构的影响

本文主要研究了不同烧结工艺对碳纳米管/羟基磷灰石复合材料力学性能与微观结构的影响.力学性能测试结果显示,在真空气氛下烧结的复合材料力学性能在总体上要高于Ar或N2气氛保护下烧结所得复合材料,断裂韧性的提高幅度最大,其最高值达到了2.2 MPa·m1/2,远高于纯羟基磷灰石.XRD及IR研究发现,所制备复合材料纯度高,无其它杂质.SEM观察发现,1100℃,真空下所得复合材料的致密性高,晶粒细,但碳纳米管管径增大;而Ar或N2气氛保护下所得复合材料中碳纳米管容易以原始形态保存,但孔隙率高,晶粒粗.     

Surface morphology and lattice distortion of heteroepitaxial GaInP on InP

We examine the relation between surface morphology and lattice distortions of a number of Ga_xIn_1-xP epilayers (x ≈ 0.04) grown on InP (001) substrates using atomic force microscopy (AFM) and high resolution X-ray diffractometry (HRXRD). The heteroepitaxial layers (thickness ≈ μm) were grown by low pressure metalorganic vapour phase epitaxy (MOVPE) at temperatures from 600 to 660°C. AFM images over a scale of 75 μm by 75 μm show no surface corrugations for samples grown at 640°C. For other growth temperatures between 600 and 660°C, unidirectional corrugations aligned along the [1 0] direction or a cross-hatched pattern can be seen on the sample surfaces with a typical interline separation of 10 μm. Another feature revealed by AFM is the presence, for some samples, of weak parallel corrugations along the direction making a 54° angle with the [1 0] direction. HRXRD spectra recorded first with the [110] and then with the [1 0] direction in the plane of incidence reveal an asymmetric relaxation in the sample plane accompanied by a broadening of the epilayer X-ray peak for diffraction with the [110] direction in the plane of incidence. The lattice distortion changes from tetragonal to orthorhombic as the surface corrugations appear along the [1 0] direction. Proton microprobe scans indicate that these samples are compositionally uniform so that the asymmetry is not the result of lateral variations of the alloy composition. Finally, low temperature photoluminescence from these samples shows good agreement between observed and calculated peak positions on the basis of the strains obtained from HRXRD measurements.     

Growth and photoluminescence properties of vertically aligned SnO2 nanowires

Vertically aligned SnO₂ nanowires (NWs) were grown for the first time by a vapor–liquid–solid method on c-sapphire with gold as a catalyst under Ar gas flow. Electron backscatter diffraction analysis indicated the NWs are single crystalline having the rutile structure, grow vertically along the [1 0 0] direction, and exhibit a consistent epitaxial relationship where lattice mismatch is estimated to be 0.3% along the SnO₂ [0 1 0] direction. The growth of these NWs is sensitive to many parameters, including growth duration, substrate type, source vapor concentration, and the thickness of the catalyst layer. Photoluminescence measurements at room temperature showed that the vertically aligned NWs exhibit an intense transition at 3.64 eV, a near band-edge transition which is rarely observed in SnO₂.     

TiAl金属间化合物/羟基磷灰石生物复合材料的制备及性能表征

首先采用机械合金化的方法制备出TiAl金属间化合物,用化学沉淀法制备出HA粉体,然后将二者球磨混合,经过真空热压烧结工艺制得TiAl/HA复合材料.力学性能检测结果表明,TiAl/HA复合材料的硬度比纯HA生物陶瓷要低,并且随TiAl质量分数的增加呈现降低趋势;复合材料的抗弯强度随着TiAl金属间化合物含量的增加呈上升趋势,含量为15;以下,其强度低于纯羟基磷灰石,含量处于15;到30;之间,其强度高于纯羟基磷灰石;断裂韧性高于纯HA生物陶瓷,最高可比纯羟基磷灰石提高78.7;,并且随着TiAl质量分数的增加呈上升趋势.X射线衍射结果表明复合材料中只含有TiAl金属间化合物和HA两种成分;断口扫描电镜照片显示,纯羟基磷灰石材料比较致密,而复合材料中存在一定量的气孔,其部分断裂区域显示出穿晶断裂的形态.     

Characteristics of composites based on PMMA modified gel silica glasses

Gel silica glass prepared by the sol-gel process can be modified by incorporating an organic phase into the intrinsically porous inorganic gel matrix, which results in a composite material with much improved mechanical and optical properties. Characterisation of PMMA modified gel silica glass prepared by the in situ polymerisation method using FT-Raman spectroscopy, gel permeation chromatography and the nitrogen adsorption technique are reported. Some essential problems encountered in the preparation are discussed.     

Characterization of organic adsorbates on model glass surfaces

Model silicate glasses in planar thin film structures are prepared using sol/gel techniques. A typical structure consists of 3.0–12.0 nm of glass on vapor deposited Ag. In this study, a pure silica and a 50/50 binary alumina-silica films are examined. Poly(methyl methacrylate) (PMMA) is adsorbed from chlorobenzene solution onto the surfaces. Infrared reflection (IR) spectroscopy, ellipsometry and quartz oscillator microgravimetry (QOM) are applied to characterize the PMMA/silicate glass interfaces formed. The QOM and IR data show that PMMA adsorption on the pure silica surface is irreversible with respect to removal by pure solvent rinse while on the binary glass surface and on a pure alumina surface, solvent rinses remove the initially adsorbed polymer. These results are interpreted in terms of Bronsted acid-base interactions involving the basic properties of the PMMA C=O group, the acidic nature of the silica and the more basic nature of the alumina containing surfaces. Further evidence for this interpretation is given by the IR spectral data which show broadening of the C=O stretching mode to lower frequencies for the irreversible adsorbed polymer on silica as compared with simulated spectra of non-surface bonding PMMA thin films. This spectral perturbation is interpreted as evidence for a hydrogen bonding interaction between OH groups on the silica surface and the C=O groups. The overall conclusion is that the surface of a 50/50 binary alumina-silica composition is dominated by the basic nature of alumina.     

Direct structural observation of the alignment and elongation in lyotropic chromonic liquid crystals under shear flow

The structural characterization of the orientation and elongation under shear flow in Lyotropic Chromonic Liquid Crystals (LCLCs) molecules, Sunset Yellow FCF (SSY), was performed by in situ rheological small/wide angle X-ray scattering (Rheo-SAXS/WAXS). The X-ray measurement results clearly demonstrated that the stacked aggregates were oriented and elongated to the shear direction under shear flow. Further shear rate increase caused the enhancement in the orientation and elongation with the inter-aggregate distance constant, and then the structural change decreased implying the onset of the orientation saturation at high shear rates.     

双向有序Ti3C2Tx/rGO复合气凝胶的制备及其电化学性能的研究

近年来,二维材料MXene因其优异的电化学性能引起了人们的关注,被广泛应用于电化学储能领域。然而,在组装电极过程中,MXene纳米片往往会产生严重的自堆积效应从而大幅限制了其电化学性能。设计三维结构的气凝胶是解决MXene自堆积问题同时开发高性能MXene基超级电容器电极材料的关键。本文利用氧化石墨烯(GO)改善了Ti₃C₂T_x气凝胶的力学强度,并通过双向冷铸和冷冻干燥、温和还原的方法制备了具有双向有序结构的Ti₃C₂T_x/rGO复合气凝胶(A-TGA)。A-TGA具有较好的力学性能和导电性,因此可直接作为超级电容器的电极材料。同时,双向有序的独特结构为电解质离子提供了无阻碍的传输通道,大幅提升了气凝胶的电化学性能。A-TGA在电流密度为1 A·g^-1时的比电容为370 F·g^-1,在100 mV·s^-1扫速下经过5 000次循环后,电容保持率高达94%,表现出优异的循环稳定性。     

Properties of Well-Aligned Polyacetylene Obtained with a Shear Proceure

We have developed a procedure to polyerize acetylene under shear conditions and graphoepitaxially in a couette type arrangement. With this procedure (CH)_n is obtained in the form of thin films consisting of highly aligned fibers. Electron diffraction patterns evidence that thepolymer chain axis is oriented parallel to the fiber direction in the (CH)_n film plane. From striations appearing perpendicular to the fiber during e-beam irradiation, from staining experiments and from dark field imaging in strong reflections of the fiber pattern it is concluded, that the (CH)_n fibers consist of lamellae with a periodicity of about 110 Å.     

Three‐dimensional numerical investigation of the effects of an open window on the convective heat transfer of an oxide Czochralski system

A three‐dimensional numerical analysis was carried out for a real Czochralski crystal growth furnace containing only gas and without any melt and crystal in order to investigate the effects of a small observation window on the temperature and flow field of the system. For this approach, the induction heating equations, the Navier‐Stokes equation with Boussinesq approximation, the continuity and energy equations have been solved in cylindrical coordinates using the finite element method. It has been found that the flow and thermal fields in the system are obviously three‐dimensional and non‐axisymmetric. The gas enters the system through the window is directed towards the opposite side wall where it is divided into two parts of vertical direction as well as expands in horizontal direction. Consequently, there is a spiral gas flow in the crucible and afterheater which rotates upwards in azimuthal direction along the walls. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)