Preparation and optical properties of CdTe/CdO center dot nH(2)O core/shell nano-composites in aqueous solution

The deposition of CdO center dot nH(2)O On CdTe nanoparticles was studied in an aqueous phase. The CdTe nanocrystals (NCs) were prepared in aqueous solution through the reaction between Cd2+ and NaHTe in the presence of thioglycolic acid as a stabilizer. The molar ratio of the Cd2+ to Te2- in the precursory solution played an important role in the photoluminescence of the ultimate CdTe NCs. The strongest photoluminescence was obtained under 4.0 of [Cd2+]/[Te2-] at pH similar to 8.2. With the optimum dosage of Cd(II) hydrous oxide deposited on the CdTe NCs, the photoluminescence was enhanced greatly. The photoluminescence of these nanocomposites was kept constant in the pH range of 8.0-10.0, but dramatically decreased with an obvious blue-shifted peak while the pH was below 8.0. In addition, the photochemical oxidation of CdTe NCs with cadmium hydrous oxide deposition was markedly inhibited.

Prediction of Effective Moduli of Carbon Nanotube-Reinforced Composites with Waviness and Debonding

Carbon nanotubes (CNTs) have been regarded as ideal reinforcements of high-performance composites with enormous applications. However, the waviness of the CNTs and the interfacial bonding condition between them and the matrix are two key factors that influence the reinforcing efficiency. In this paper, the effects of the waviness of the CNTs and the interfacial debonding between them and the matrix on the effective moduli of CNT-reinforced composites are studied. A simple analytical model is presented to investigate the influence of the waviness on the effective moduli. Then, two methods are proposed to examine the influence of the debonding. It is shown that both the waviness and debonding can significantly reduce the stiffening effect of the CNTs. The effective moduli are very sensitive to the waviness when the latter is small, and this sensitivity decreases with the increase of the waviness. (C) 2008 Elsevier Ltd. All rights reserved.

High-Strength Composite Fibers: Realizing True Potential of Carbon Nanotubes in Polymer Matrix through Continuous Reticulate Architecture and Molecular Level Couplings

Carbon nanotubes have unprecedented mechanical properties as defect-free nanoscale building blocks, but their potential has not been fully realized in composite materials due to weakness at the interfaces. Here we demonstrate that through load-transfer-favored three-dimensional architecture and molecular level couplings with polymer chains, true potential of CNTs can be realized in composites as Initially envisioned. Composite fibers with reticulate nanotube architectures show order of magnitude improvement in strength compared to randomly dispersed short CNT reinforced composites reported before. The molecular level couplings between nanotubes and polymer chains results in drastic differences in the properties of thermoset and thermoplastic composite fibers, which indicate that conventional macroscopic composite theory falls to explain the overall hybrid behavior at nanoscale.

Photorefractive performance of a novel multifunctional inorganic-organic hybridized nanocomposite sensitized by CdS nanoparticles

A novel multifunctional inorganic-organic photorefractive (PR) poly(N-vinyl)-3-[p-nitrophenylazolcarbazolyl-CdS nanocomposites with different molar ratios of US to poly(N-vinyl)-3-[p-nitrophenylazo]carbazolyl (PVNPAK) were synthesized via a postazo-coupling reaction and chemically hybridized approach, respectively. The nanocomposites are highly soluble and could be obtained as film-forming materials with appreciably high molecular weights and low glass transition temperature (T,) due to the flexible spacers. The PVNPAK matrix possesses a highest-occupied molecular orbital value of about -5.36 eV determined from cyclic voltammetry. Second harmonic generation (SHG) could be observed in PVNPAK film without any poling procedure and 4.7 pm/V of effective second-order nonlinear optical susceptibility is obtained. The US particles as photosensitizers had a nanoscale size in PVNPAK adopting transmission electron microscopy. The improvement of interface quality between US and polymer matrix is responsible for efficient photoinduced charge generation efficiency in the nanocomposites. An asymmetric optical energy exchange between two beams on the polymer composites PVNPAK-CdS/ECZ has been found even without an external field in two-beam coupling (TBC) experiment, and the TBC gain and diffraction efficiency of 14.26 cm(-1) and 3.4% for PVNPAK-5-CdS/ECZ, 16.43 cm(-1) and 4.4% for PVNPAK-15-CdS/ECZ were measured at a 647.1 nm wavelength, respectively.

Enhanced photoresponse from the ordered microstructure of naphthalocyanine-carbon nanotube composite film

Naphthalocyanine-sensitized multi-walled carbon nanotube (NaPc-MWNT) composites have been synthesized through the pi-stacking between naphthalocyanine (NaPc) and carbon nanotubes. The resultant nanocomposites were characterized with a scanning electron microscope (SEM), a transmission electron microscope (TEM), and by UV - vis absorption and photocurrent spectra. The long-range ordering was observed in the NaPc - MWNT composites by using a TEM. The enhancement in the absorption intensity and the broadening of the absorption wavelength observed in the composite films, which were due to the attachment of NaPc on the MWNT surface, is discussed based on the measured UV - vis absorption spectra. Furthermore, the photoconductivity of the poly( 3-hexylthiophene)(PAT6) - NaPc - MWNT composite film was found to increase remarkably in the visible region and broaden towards the red regions. These new phenomena were ascribed to the larger donor/acceptor (D/A) interface and the formation of a biconsecutive D/A network structure, as discussed in consideration of the photoinduced charge transfer between PAT6 and NaPc - MWNT.

高真空强静电场下聚合物结构和形态研究

聚合物是一类软物质，软物质最典型的特征是对外场的影响易于作出响应。在外场如电场、磁场、温度场和微重力场等作用下，其内部结构会发生一系列变化，对于聚合物其分子链的构象及分子链的堆积等均有可能发生转变。通过控制外场类型和强度可以实现对聚合物材料结构的调控，从而使聚合物材料的功能能适应外界条件的变化，满足不同环境的需要。外场对聚合物形成的影响是目前聚合物材料研究的一个热点。本文目的是研究高真空强静电场对聚合物结构和形态的影响，在自行设计制造的高真空强静电场装置上进行了聚合物熔融结晶、共混物半熔融态处理和聚合物薄膜微晶生长实验，使用XRD、DSC和SEM等研究手段对上述实验样品进行了分析和观察，实验发现，随静电场强度的增大，熔融结晶的等规聚丙稀和间规聚苯乙稀的XRD峰均向低角度偏移，导致等规聚丙稀晶格参数增大，晶胞膨胀，而间规聚苯乙稀逐渐由α型向β型转变，等规聚丙稀随静电场强度的增大，逐渐由球晶变为沿电场方向取向的厚片晶，间规聚苯乙稀由混乱的片晶变为有取向规整的片晶；在强静电场下，半熔融处理的PA11／PVDF共混物，随电场强度的增加，PA11逐渐由α型向δ型转变，共混物由球晶逐渐变为沿电场方向取向的柱状晶；同样，随电场强度的增加，聚合物薄膜微晶由树枝形球晶转变成沿电场方向取向的树枝晶，且在强静电场下部分聚合物的树枝发生断裂。总之，在聚合物固化过程中施加强静电场将对聚合物的结构和形态转变产生较大的影响。

尺寸诱导的聚合物亚稳结晶

亚稳定性是凝聚态物质的一个重要特征。常温常压下，热力学上不稳定的、而实际上存在的相，都可称之为亚稳相。通常，影响物质亚稳态存在的外界因素有温度、压力、电场、磁场等等，而相态本身的大小也是决定它稳性的一个重要因素，这就是所谓的尺寸效应。随着纳米技术和微处理器技术的飞速发展，材料的应用尺寸日趋于小型化和微型化。研究聚合物相行为和相变中的尺寸效应，对于充分理解高分子凝聚态物理学的基本问题具有极度其重要的科学意义，它还为纳米科技中材料特殊的结构和性能提供新的认识途径和理论基础，这必将极度大地促进纳米材料的实用化进程。本文正是基于这样一种相变中的尺寸效应，选用了三种具有多晶型结构的结晶聚合物，聚偏氟乙烯（PVDF），聚反式1,4-丁二烯（TPBD）和尼龙1010（nylon 1010），对它们的晶体结构及其相转变过程和转变条件作了较详细的研究，着重探讨了各种晶型稳态和亚稳态的存在条件。在这三种聚合物当中，发现小尺寸晶体趋向于形成二维高有序的六方或拟六方堆积结构，成功地证明了晶体结构对尺寸的依赖性。在上述研究中，首次成功地为PVDF营造了不同程度的空间受限结晶环境，得到了尺寸小于100纳米受限结晶的亚稳态β晶；通过结合使用常温和低温的电子衍射术，并利用计算机模拟技术，提出了尺寸影响的TPBD相转变的具体实现过程；发现了培养尼龙1010单晶的另一理想溶剂二甲基甲酰胺（DMF），并首次用它培养出十分完善的单晶体；引入尺寸效应的观点来解释尼龙1010的Brill转变现象，定量地确定了基转变温度对尺寸的依赖关系，为解释这一古老但至仿仍存在极大争议的尼龙中特有的转变现象开辟了创造性的思维方式；首次用极度稀溶液喷雾法获得了尼龙1010的纳米和微米级微纤维晶，并解释了它的形成原因。

疏水微孔膜的制备及应用

疏水微孔膜主要应用于膜蒸馏、渗透蒸馏以及膜接触器等膜分离过程中。近年来随着这些膜过程应用研究的蓬勃开展，高性能疏水微孔膜的研制逐渐引起人们的广泛关注。在已经开发的疏水性膜材料中，聚四氟乙烯、聚丙烯微孔膜虽然表现出高强度、高疏水性、高抗化学腐蚀性等优异的综合性能，但其复杂的加工工艺，使其难以大规模的推广普及。聚偏氟乙烯是迄今为止唯一可以采用Loeb-Souirajann相转换法这种相对简单的工艺制膜的疏水性材料，但其较差的机械性能有可能成为其工业化应用的瓶颈。因此进一步开发新型高性能的疏水性膜材料，对于拓宽膜材料的来源，加快膜蒸馏等新型膜过程的工业化步伐具有重要的意义。本论文以F26和F24为对象，系统研究了Loeb-Sourirajann相转换制膜过程中各种操作条件对F26和F24微孔膜结构的影响，首次制备出能够应用于膜蒸馏、渗透蒸馏等新型膜过程的F26、F24疏水微孔膜。其次，通过优化各种制膜条件，所制F26、F24微孔膜的渗透性能优于相同条件下的PVDF微孔膜。与国外商品膜的比较表明：自制微孔膜的孔隙率较高，膜蒸馏组件常数与商品膜可比。第三，使用自制的F26微孔膜处理2wt.％的板蓝根溶液，当将其浓度浓缩到20wt．％时，没有检测到有效成分的损失，显示了微孔膜良好的应用前景。第四，自制F26、F24微孔膜的疏水性强于采用相同方法制备的PVDF微孔膜。机械性能的比较也表明F26、F24微孔膜优于相同条件下的PVDF膜。特别是F24微孔膜在拉伸应变和断裂伸长率方面高于PVDF微孔膜8倍之多。第五，使用乙二醇作为添加剂制备F26微孔膜的过程中，在F26微孔膜的上表面首次发现排列规则的大孔现象。利用二甘醇、草酸等作为添加剂时，也发现了同样的现象。这对于丰富微孔膜结构信息，完整地描述多孔皮层的形成机理提供了新的证据。

裂解型高聚物的共混辐射交联

本文对聚甲基丙烯酸甲酯（PMMA）和聚异丁烯（PIB）两种典型的辐射裂解型高聚物的共混体系聚甲基丙烯酸甲酯-聚氧化乙烯（PEO），聚甲基丙烯酸甲酯-聚偏氟乙烯（PVDF），和聚异丁烯-乙丙共聚物（EPR）进行了较为详细的研究，结果表明：1、PMMA-PVDF共混体系溶胶抽提发现，在此共混体系中，PMMA发生裂解，且随辐照剂量增加，体系可被抽出量增加，符合关系（D_o-D_R) = KR + b k，b是常数，R为剂量，D是归一后的PMMA的相对剩余量，PMMA在共混体系（PMMA-PVDF）中的辐射裂解遵守无规降解规则，适合1/((M-bar)_n) = K (R_o + R)关系。PMMA的裂解程度可直接由溶胶抽提决定。机械性能测定表明，PVDF的存在，对PMMA的机械性能的辐射损伤有保护作用，少量PVDF的加入，不影响材料的透明性，抗冲击强度大为增加，且经一定剂量辐照后，抗张强度和断裂伸长无显下降。结晶分析发现，PVDF不论在共混体系或均聚物中，经辐照到一定高的剂量，其DSC曲线上的结晶熔峰分裂为双重。和国外文献报道的结果正相反。由此得出PVDF中多种晶型的存在，及晶型在一定温度发生转化。2、PMMA-PEO共混体系 凝胶抽提，热形变测定，付立叶变换红外光谱和动态力学粘弹谱测定都证明，PMMA和PEO共混以后，无论是在真空，还是在空气中辐照，PMMA发生了交联。并且交联是在一定的PEO-PMMA混合配比和一定辐照剂量范围内进行的。在某一配比时，交联率达最高。用扫描电镜和透射电镜对共混体系的相结构形态进行研究表明。交联最好的组成比是在PMMA-PEO共混体系的相倒转点附近。溶液共混时，PMMA-PEO体系的互溶程度与共混的温度条件有关，温度高于PEO的熔点时，共混体系的互溶性要比常温时共混要好，这和理论预测的结果一致。红外分析的结果说明，PMMA的交联主要是通过残基结合的方式进行的。3、PIB-EPR共混体系 采用低温DSC对PIB-EPR共混体系的互溶性进行了研究，发现PIB-EPR的互溶性较好，其Tg转变为-拓宽的单峰。凝胶抽提指出，聚异丁烯经与乙丙共聚物共混以后，在一定配比和一定辐照剂量范围内，聚异丁烯发生了交联，且在一定配比时交联率达到最高。交联是否发生，还与共混的方式有关，溶液共混时不发生交联。低温DSC研究显示，溶液共混时，其互溶性不如机械共混时PIB与EPR的互溶性好，前者的Tg转变呈现出分裂的双峰。4、裂解型高聚物与交联型高聚物共混以后，是否可以发生交联，首要的是体系的互溶程度，体系越均匀，交联的可能性越大（但不是充分条件）。由于互溶性不好，PMMA和很多橡胶共混合不产生交联，PIB与1，2-PBD以及和其它一些不饱和橡胶共混合不产生交联。在PIB，1，2-PBD共混体系的DSC分析曲线上，Tg转变是两独立的双峰，对应于PIB和1，2-PBD的Tg转变。交联的可能性能否实现，还与交联聚合物的链结构，柔顺性，及两种分子链间的相互作用有关。PMMA与PEO和PVDF两者的共溶性都很好（分子水平上），但前者可交联，而同后者共混后则裂解。

微孔憎水膜结构控制及基与膜蒸镏行为的关系

膜蒸镏是以蒸气压差为驱动力的新的膜过程，与基它膜过程相比，其优点是在常压和适中的温差条件下进行，并可以处理极高浓度的溶液。本工作首先用聚偏氟乙烯为膜材料制备疏水性微孔膜，研究了用于膜蒸镏的PVDF膜孔结构控制问题，用三元相图讨论了各种制膜因素如：添加剂用量、分子量；聚合物浓度，混合溶剂比；凝固浴组成与温度对膜 孔结构的影响。本工作对每一条件形成的膜的断面都做了扫描电镜图示分析，归纳了膜孔结构随条件变化的规律，同时也讨论了这些制膜因素与膜蒸镏性能的关系。研究结果表明，控制添加剂PEG分子量在1000左右，PEG/PVDF在20/80左右，固含量在10～12%之间，Ac-DMF混合溶剂 Ac/DMF > 40/60（或纯DMF溶剂），无需蒸发时间，凝固浴组成：水／乙醇 ＜ 7/3（δ在18.0左右），凝固浴温度40 ℃左右，能够得到较好的适合于膜蒸镏的憎水微孔PVDF膜。我们还研究了膜后处理问题，用红外光谱定量分析添加剂含量，通过添加剂含量对水、乙醇浸泡、酸煮和乙醇－水萃取等处理方法进行了评价。其次，我们对用辐照法或等离子体法在通用纤维素类膜上接枝或镀上憎水单体使亲水膜憎水化进行了研究。研究结果表明，CA膜辐照接枝苯乙烯时，Pyd/St控制在10/90左右较好，并能够得到适用于膜蒸镏的改性憎水膜。等离子体法镀膜要注意镀层均匀性。我们还着重研究了凝固浴组成对PVDF膜孔结构的影响，确定了选择凝固浴介质的物化原则，建立了凝胶介质溶解度参数与孔结构的定量关系。认为：r_f = A (δ - δ')~2 + B δ > δ'时膜为指状孔结构，δ < δ'时膜为海绵状结构。我们还讨论了PVDF膜的一些蒸镏特性，结果表明，海绵状或具有较小指状孔结构的PVDF膜，不易被润湿，适合于膜蒸镏。

高效膜蒸馏用膜及其膜蒸馏的研究

膜蒸馏是一种以水蒸汽压差为推动力的新型膜过程，可望在海水及苦咸水淡化、高纯水制备、化学物质浓缩与分离和废水处理等方面得到应用。但膜蒸馏由于通量较低，至今未能在大规模工业生产中得到应用。膜蒸馏用疏水微孔膜的结构和性能是影响膜蒸馏通量的重要因素，如何制备高效膜蒸馏用膜是当前迫切需要解决的问题。本论文主要围绕制备高通量的膜蒸馏用疏水微孔膜，采用多种制膜手段进行了系统的研究，取得了较好的结果。首先，以疏水的聚偏氟乙烯为膜材料，利用相转换法制备出了高效膜蒸馏用聚偏氟乙烯疏水微孔膜。通过对各种制膜条件的系统研究，使聚偏氟乙烯微孔膜的形态结构能得到有效的控制。在研究中，利用无机盐氯化锂为添加剂来代替传统的水溶性高分子添加剂，解决了添加剂残留于膜中而影响膜的膜蒸馏性能的问题，提高了PVDF微孔膜的截留率和膜蒸馏通量，使其通量达到反渗透膜过程的水平。其次，首次采用等离子聚合和聚合物表面涂敷的方法将亲水性微孔膜疏水化，使之能够用于膜蒸馏中，大大地拓宽了膜蒸馏用膜材料的选择范围。同时改性得到的疏水复合膜的膜蒸馏通量超过了文献报道的数值，解决了膜蒸馏通量低的问题，为膜蒸馏的实用化奠定了良好的基础。除了高效膜蒸馏用膜的研究外，本论文还进行了膜蒸馏的应用研究，首次发现膜蒸馏能够用于分离共沸混合物，为膜蒸馏的应用开辟了新的途径。

Preparation and characterization of multiwalled carbon nanotube-supported platinum for cathode catalysts of direct methanol fuel cells

Multiwalled carbon nanotube-supported Pt (Pt/MWNT) nanocomposites were prepared by both the aqueous solution reduction of a Pt salt (HCHO reduction) and the reduction of a Pt ion salt in ethylene glycol solution. For comparison, a Pt/XC-72 nanocomposite was also prepared by the EG method. The Pt/MWNT catalyst prepared by the EG method has a high and homogeneous dispersion of spherical Pt metal particles with a narrow particle-size distribution. TEM images show that the Pt particle size is in the range of 2-5 nm with a peak at 2.6 nm, which is consistent with 2.5 nm obtained from the XRD broadening calculation. Surface chemical modifications of MWNTs and water content in EG solvent are found to be the key factors in depositing Pt particles on MWNTs. In the case of the direct methanol fuel cell (DMFC) test, the Pt/MWNT catalyst prepared by EG reduction is slightly superior to the catalyst prepared by aqueous reduction and displays significantly higher performance than the Pt/XC-72 catalyst. These differences in catalytic performance between the MWNT-supported or the carbon black XC-72-supported catalysts are attributed to a greater dispersion of the supported Pt particles when the EG method is used, in contrast to aqueous HCHO reduction and to possible unique structural and higher electrical properties when contrasting MWNTs to carbon black XC-72 as a support.

Preparation and characteristics of nonflammable polyimide materials

The thermal and flame-retardant properties of homo- and copolyimides were evaluated. Those containing sulfone linkages in the backbone were found to be more flame retardant. Both properties were dependent on the composition. A polyimide/silica nanocomposite was obtained through sol-gel processing. The effects of the addition of silica an the dispersion, interfacial adhesion, fire resistance, mechanical properties, and thermal stability of the composites were investigated. SEM analysis showed a good dispersion of silica with a diameter of 50-300 nm in the organic matrices. The addition of silica increased the fire retardancy and mechanical properties of the composites. (C) 2000 John Wiley & Sons, Inc.