【作者】 张世玲；

【导师】 武利民；

【作者基本信息】 复旦大学 ， 材料物理与化学， 2010， 博士

【摘要】 有机-无机复合材料兼具有两组分的优势,并赋予材料新的结构和性能。聚合物乳液与纳米SiO2结合,是提高聚合物性能的重要途径。文献中对聚合物/SiO2纳米复合乳液的制备方法、复合粒子形态、复合涂层的性能等方面进行了大量研究。但人们的兴趣主要集中在以上三个方面,且复合乳液的成膜温度一般为环境温度。本论文基于聚合物/SiO2纳米复合乳液,将其直接在不同的温度下干燥,分别得到三维有序大孔聚合物膜和表面形貌梯度材料,并进一步利用该乳液为二元粒子体系,将其用作模板,采用原位自组装法制备了多级有序多孔材料,从而为传统的聚合物/SiO2纳米复合乳液开发了新的用途。具体的研究内容和结果如下：(1)采用无皂乳液聚合法和分散聚合法制备一系列单分散的聚合物微球分散液,再与SiO2纳米粒子混合均匀,得到稳定的纳米复合乳液。将此复合乳液直接在较高的温度下强迫干燥,成功制备了三维有序大孔聚合物膜,制备过程无需去除模板,方法简单、价廉且环境友好,可进行大量制备。然而,要得到有序大孔结构的聚合物膜,必须首先保证复合乳液的稳定性,聚合物微球和二氧化硅纳米粒子之间的强的静电排斥作用是制备稳定纳米复合乳液的必要条件。在此基础上,详细考察了形成大孔结构的条件和影响因素,研究发现,聚合物玻璃化转变温度(Tg)、聚合物微球壳层亲水组分的含量、SiO2纳米粒子的粒径、聚合物微球的粒径、分散介质的挥发速度以及聚合物微球的结构对孔的形成和结构都有重要的影响,而采用聚合物空球则有望制备相互连通的大孔结构。SEM的形貌观察和USAXS的晶面衍射结果表明,得到的有序大孔膜属于典型的面心立方(FCC)结构。调整乳液的干燥程序,综合XPS、TGA和SEM等实验结果,大孔结构可能的形成机理为：复合乳液的干燥从气-液的界面开始,孔的形成也从膜的表面开始,随着介质的蒸发,孔的形成逐层进行,并一层层向基材推进,最终形成三维有序的大孔结构。制得的有序大孔聚合物膜具有光子晶体效应,呈现结构色,并对不同折光指数的溶剂和乙醇/水介质具有光学响应性。该技术为有序多孔膜的制备提供了新的范例,所得到的有序多孔膜可应用于光子晶体、生物传感、模板、催化剂载体等。(2)基于聚合物/SiO2纳米复合乳液,进一步控制复合乳液的干燥条件,直接在较低的温度下干燥,可直接得到有序多孔的表面形貌梯度,制备过程简单快速,不需精确控制梯度参数。聚合物的Tg、分散介质、复合乳液的干燥温度以及SiO2的含量对表面形貌都有显著影响。当聚合物的Tg相对较低时,在室温或稍高的温度下干燥均可制备形貌梯度表面；而当聚合物的Tg较高时,则不能形成形貌梯度表面。而当干燥温度较高时,得到的复合膜为三维有序的大孔结构,而不能形成表面形貌梯度。干燥温度对复合膜形貌的影响可能是由于不同的成膜机理造成的：当成膜温度较低时,成膜过程遵循对流自组装机理；而在较高的温度下干燥时,成膜过程主要遵循气-液界面自组装机理,而在中间温度干燥时,则这两种机理同时发挥作用。该方法提出了一种制备聚合物表面形貌梯度的新方法,该方法有望用来制备其它功能性有机和无机组分的表面形貌梯度材料。(3)基于聚合物/SiO2纳米复合乳液的二元粒子体系,以蔗糖为碳源,硫酸为碳化催化剂,采用原位自组装法制备多级有序多孔炭材料。该方法将纳米复合乳液在程序升温过程中,历经干燥成膜、初步碳化和最终碳化过程得到三维有序大孔碳/SiO2复合膜,最后除去SiO2纳米粒子,得到有序大孔/介孔炭材料。与常用的其它模板法相比,该方法既不需预先合成多级有序多孔硬模板或胶体晶体模板,也不需额外的反填,聚合物胶体晶体的形成过程和碳源的填充在同一体系中同时完成。因此,制备过程非常简单快捷,大孔和介孔的尺寸可分别进行调节,其中,介孔的尺寸可以在整个介孔的范围内进行调节。BET结果表明,所制得多孔炭材料具有较高的比表面积和孔容；XRD和R(?)an光谱分析表明,该多孔炭材料具有部分石墨化的结构。为检验其载体效应,用甲酸还原法将制得的多级有序多孔炭用作Pt-Ru合金催化剂载体,与商业Pt-Ru合金催化剂相比,在甲醇燃料电池中对甲醇的氧化反应具有更优异的催化性能。更多还原

【Abstract】 Organic-inorganic composite materials combine the advantages of the two components, and have novel structures and properties. Combination of polymer latex with SiO2 particles is an important strategy to improve the properties of polymeric materials. Recently, researchers have done a lot of work on the preparation of polymer/SiO2 nanocomposite latex, morphology of composite particles, and properties of composite coating. But most of the researches only focus on the above three fields, and on the film-formation at ambient temperature. In this dissertation, when polymer/SiO2 nanocomposite latex was forced-dried at different high temperatures,3-dimensional-ordered-macroporous (3-DOM) film and surface morphology gradient can be directly obtained, respectively. We also use the nanocomposite latex as binary particle system, and prepared hierarchically ordered porous carbon via in-situ self-assembly of polymer spheres and silica particles with carbon source. All the research content and results are as follows:(1)A series of colloidal polymers with various Tg, composition, and sphere size were synthesized by surfactant-free emulsion polymerization and dispersion polymerization methods and then blended with colloidal silica particles to obtain stable polymer/silica nanocomposite latexes. When these nanocomposite latexes were forced dry at relatively high temperature (e.g.,110℃) for 2 h, a 3-DOM structure was directly obtained. Neither complex processes nor removal of any templates like in a templating method was needed. Therefore, it is really feasible, inexpensive, and environmentally friendly. More importantly, this process can be used for a large-scale fabrication of ordered porous polymer films. However, the strong repulsive force between polymer sphere and colloidal silica particles is necessary to successfully prepare the stable nanocomposite latex and then the ordered porous film. In addition, we investigated the effects of some key parameters, e.g., polymers with various glass transition temperature (Tg), composition, hydrophilic component, structure and sphere size, solvent with different volatility and silica particle size on the formation of ordered porous film, and tried to really understand the formation mechanism of this ordered porous structure via the forced-drying strategy, these ordered pores should form from the top surface and then propagate layer by layer from the top surface to substrate. The films are typical faced-centered-cubic structure, and show structure colors, and can be used as solvent sensors.(2) The second part presents a novel and feasible approach for fabrication of morphological gradient surfaces based on the film-formation of nanocomposite polymer latex. In this method, when the polymer latex with relatively low Tg was blended with colloidal silica and then dried at certain temperatures, a morphological evolution with deeper pores from the center to the edge could be directly obtained on polymer surface. Neither careful control of experimental conditions nor any complex processes are needed. The Tg of polymer, the silica content, the solvent and the drying temperature have significant influences on this surface morphology. The film-formation mechanisms at different drying temperatures are also discussed.(3) The third part presents an one-pot method to synthesize hierarchically ordered porous carbons with interconnected macropores and mespores, via in-situ self-assembly of colloidal polymer and silica spheres with sucrose as carbon source. Compared with other techniques, this procedure is veritably simple, neither pre-synthesis of the macropore/mesopore or crystal templates nor additional infiltration is needed, the self-assembly of polymer spheres into crystal template and the infiltration are finished in-situ in the same system. The sizes of macropores and mesopores can be independently tuned by the sizes of polymer and silica spheres, respectively. The obtained bimodal porous carbons have large BET surface areas, large pore volumes, and partially graphitized frameworks. And they show very good supports of Pt-Ru alloy catalyst in direct methanol fuel cell.更多还原