论文标题:碲化镉纳米晶的制备及其与聚合物的复合
Study on the Preparation and Composites of CdTe Nanocrystals
论文作者 张皓
论文导师 杨柏,论文学位 博士,论文专业 高分子化学与物理
论文单位 吉林大学,点击次数 112,论文页数 145页File Size5123k
2004-04-01论文网 http://www.lw23.com/lunwen_14053387/ 建筑性,现代性,存在美学,实践美学,中国语境,现代性现象学
architecturity,modernity,being aesthetics,practical aesthetics, Chinese context,modernity phenomenology
具有光致荧光性质的半导体纳米晶，在光电转换、传感、光学显示、及生物成像等领域具有潜在的应用价值。实现这些纳米晶的实际应用，就需要将它们复合进惰性介质中。在本论文中，我们针对水溶性 CdTe 纳米晶，以最终制备纳米晶与聚合物的功能性复合物为目的，系统的研究了纳米晶的制备方法，对纳米晶进行了精确的表面修饰，从而制备出一系列的膜相、体相、液相复合材料，并实现了对复合材料的微加工。 首先，我们建立了以 NaBH4还原 Te 粉制备 NaHTe，并与 CdCl2反应得到 CdTe 纳米晶前驱体的廉价方法，考查了制备条件对纳米晶光谱性质的影响。发现 Cd-SR: HTe-的比例，前驱体浓度，前驱体溶液 pH 值，稳定剂结构等对纳米晶都有重要影响。以此为基础，发展了一种在低前驱体浓度，及中温水热条件下制备高质量 CdTe 纳米晶的新方法。高温加快了纳米晶的生长速率和荧光半峰宽的窄化。不需要任何后处理，黄绿光样品的室温量子效率就可以超过 30 %。该方法弥补了水相合成不利制备较大尺寸纳米晶的缺点。产品纳米晶可直接用于标记各种蛋白和细胞，潜在应用于生物成像。 为了更好的实现纳米晶与聚合物的复合，我们研究了表面修饰对 CdTe纳米晶光谱性质的影响。我们以传统的层状组装方法为桥梁，建立了系统研究纳米晶表面结构的新方法。该方法是利用表面带负电荷的 CdTe 纳米晶与 I摘 要带正电荷的聚电解质交替沉积组装成 CdTe 纳米复合膜，避免了溶液中杂离子的干扰，最大程度上保持了纳米晶表面结构。用表面光电子能谱表征与CdTe 纳米晶相关的元素，可得到纳米晶组成的信息，从而推算纳米晶表面结构的变化。回流过程，适当的酸碱性可以促进巯基羧酸和 Cd2+离子复合物在纳米晶表面的沉积。由于这层复合物的存在，不同的巯基羧酸具有各自的 pH 值敏感最佳发光。多聚羧酸在适当的 pH 值下也可以增强发光，结合荧光光谱和 XPS 表征，系统的考察了羧基对 CdTe 纳米晶光致发光及稳定性的影响。羧基和纳米晶表面 Cd2+离子的配位可以有效提高纳米晶的发光强度。这一现象只能在酸性条件下才能观察到，说明羧基和纳米晶表面的相互作用可以有效减弱电子-空穴间的非辐射复合，转化为辐射复合。 利用多聚羧酸对 CdTe 纳米晶的表面修饰，进一步构筑了水溶性纳米晶与非水溶性咔唑/吡啶共聚物的交替沉积膜。多聚羧酸被证明是一种有效的中介物增加了纳米晶与共聚物间的相互作用，红外光谱证明成膜驱动力为氢键相互作用。通过控制咔唑、吡啶基团在共聚物中的比例，CdTe 溶液中多聚羧酸的浓度，实现了 CdTe 纳米晶和咔唑两类荧光体在膜中的可控沉积。利用 CdTe 纳米晶与重氮树脂间的静电相互作用制备了自组装沉积膜。在紫外光照射下将 CdTe 纳米晶与重氮树脂间的连接方式由离子键转化成共价键，有效提高了基于纳米晶超薄膜的稳定性。先用多聚羧酸修饰纳米微粒，然后静电组装，最终形成共价键连接的方法，还被用于制备含 Fe3O4纳米微粒的超薄膜。 利用静电相互作实现了可聚合表面活性剂对 CdTe 纳米晶的表面修饰，将纳米晶从水相转移到油相。可聚合表面活性剂修饰的 CdTe 纳米晶可以和自由基单体共聚，制备出纳米晶-聚合物复合体材料。自由基单体可以是苯乙烯，也可以是甲基丙烯酸酯类单体。可聚合表面活性剂的使用，提高了纳米晶与聚合物的相容性，防止了纳米晶的相分离，对复合材料的透明性至关 II张皓 吉林大学博士学位论文 2004重要。纳米晶充当了交联点。系统研究了季铵盐类分子结构、纳米晶表面稳定剂种类、及相转移条件对复合物性能的影响。纳米晶表面的巯基羧酸稳定剂层起到保护荧光的作用，防止了加热聚合过程中自由基对荧光的淬灭。巯基丙酸的稳定效果比其它巯基羧酸的稳定效果好。另外，我们还通过溶胀交联聚苯乙稀微球的方法制备了亚微米尺寸的复合荧光微球。用季铵盐类两亲性大分子对 CdTe 纳米晶直接进行表面修饰，制备了油溶性纳米晶-聚合物复合物，纳米晶充当了物理交联点。纳米晶无需经受加热聚合过程，就可以得到与聚合物的复合物，回避了自由基对荧光的淬灭。该复合物具有良好的可加工性，能够灵活的被加工成各种宏观形状的纤维，利用这些纤维，我们构造出荧光防伪条形码。结合软光刻技术、诱导水滴冷凝技术和去润湿过程，实现了复合物的图案化。首次以制备好的纳米晶-聚合物复合物为原料，并结合分散乳化技术，制备了微米尺寸的复合荧光微球。
Highly fluorescence (PL) semiconductor nanocrystals have wide applicationsin optoelectronic conversion, sensor, optical display, and especially biologicalimaging. Making these nanocrystals to real-world application, it is required tostabilize them in inert matrices. Attention is paid on water-soluble CdTenanocrystals in this thesis that the preparation and surface modification ofnanocrystals, and the assembly of nanocrystals with polymers for compositefilms, bulks, and solutions are investigated in detail. First, we develop a simple and cheap method to prepare water-soluble CdTenanocrystals by using the materials of Te powder and CdCl2. The Cd-SR/HTe-ratio, the concentration of precursor, the pH of precursor, and the structure ofstabilizer are important in the preparation of CdTe nanocrystals. Based on theseresults, we develop a method to high quality CdTe nanocrystals under the lowprecursor concentration, and middle hydrothermal condition. High temperatureaccelerates the growth rate and full width at half maximum (FWHM) narrowingof nanocrystals. Without any post-treatment, the quantum yields (QY) are up to30 % for green-yellow samples at room temperature. Our approach is a simpleand cheap method to produce high-quality nanocrystals with good biologicalcompatibility. We investigate the influence of surface modification on the spectral propertiesof CdTe nanocrystals for the further assembly of them with polymers. The IV张皓 吉林大学博士学位论文 2004popular method of constructing multilayer films is adopted as a tool tocharacterize surface composition of CdTe nanocrystals. By this method, theinterference of small molecular in solution is avoided without destroying theimportant surface composition of nanocrystals. Combined with XPS and opticalspectroscopy, the correlation between CdTe PL intensity and particle surfacecomposition is analyzed systematically. It is experimentally observed that Cd-SRcomplexes on the surface of the CdTe nanocrystals provide the crucial chemicalpassivation responsible for the high PL intensity of CdTe nanocrystals.Ploy(carboxylic acid) can also enhance the CdTe PL at proper pH range.Systematic pH-dependent photoluminescence and XPS studies havedemonstrated that carboxyl groups have a great influence on bothphotoluminescence and stability of the mercaptocarboxylic acid stabilized CdTenanocrystals. The coordination between the carboxyl groups and cadmium ionscan effectively improve the PL efficiency of the CdTe nanocrystals. But thisenhancement effect is only observed in certain acidic range, which suggests that,the interaction between carboxyl groups and the CdTe particle surface caneffectively diminish the nonradiative channel for electron-hole recombination. In this section, poly(acrylic acid) (PAA) acts as an important medium toenhance the interaction between nonionic copolymers and aqueous CdTenanocrystals. PAA has a strong coordinative interaction with CdTe nanocrystalsin acidic range via the interaction between the carboxyl in PAA and the cadmiumon the surface of CdTe. Meanwhile, the strong H-bonding interaction betweenPAA and pyridine groups in copolymers makes it possible to fabricate depositedfilm. As characterized by optical spectroscopy, IR spectroscopy and TEM, ourresults show that CdTe nanocrystals can be embedded into carbazole-containingcopolymers using layer-by-layer (LBL) assembly technique. Moreover, thephotoluminescence of the resulted films can be tuned by using copolymers withdifferent ratio of pyridine/carbazole and CdTe solutions with different PAAconcentration. A precursor film has been fabricated from CdTe nanocrystals andnitro-containing diazoresin (NDR) using electrostatic interactions and thestandard LBL assembly method, covalent bonds are formed under ultravioletirradiation. The long-term stability of these films has been d
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