单分散无机/PNIPAM核壳纳米结构的设计合成及其性能研究

There has been increased interest in coating surfaces of nanoparticles with a shell of stimuli-responsive polymer for their prospective applications in fields such as catalysis, photonics, electronics, optics and biomedicine. Among these, nanoparticles coated with thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) have been extensively studied for PNIPAM dissolved in water could undergo a clear-to-opaque transition at a temperature exceeding its lower critical solution temperature (LCST ≈ 32 oC), which is close to the physiologic temperature of human body, and nanospheres with PNIPAM as shell have been applied to biomedical field such as nucleic-acid extraction and purification, controlled release, and cell-culture substrates. However, during the traditional method to inorganic/PNIPAM core-shell nanostructures, the formation of "core" and the growth of "shell" were independent and retreatment was requisite to the "core" surface otherwise the polymerization cannot be confined onto the "core" surface. As to these research project, a two-step approach was designed to obtain inorganic/PNIPAM nanostructure. In the first step, monodisperse nanoparticles were prepared using an certain chain transfer agent as surfactant, and the obtained nanoparticles can be dispersed stably in ceratin solvent (THF, CHCl3, etc) because of the hydrophobic nature of chain transfer agent absorbed on the core surface. In the second step, the polymerization was initiated and was restricted on the surface of core surface, thus nanoparticles coated with well-defined PNIPAM can be obtained. Furthermore, the good dispersity of nanoparticles in organic solvent avoided the possible agglomerization during the polymerization process. The thermoresponsive core-shell nanostructures can be applied to many fields for their function can be tailored according to different purposes by adopting different inorganic matter as core materials.

聚异丙基丙烯酰胺(PNIPAM)包覆无机纳米粒子形成的无机/PNIPAM核壳结构在催化剂、化学分离、化学传感器和药物释放等方面具有广泛的应用前景，发展新颖的无机/PNIPAM纳米核壳结构的制备方法是一项具有挑战性的课题。本申请的核心是利用PNIPAM可控聚合所需的链转移剂是表面活性剂的结构特点，首先制备出单分散纳米粒子，因其表面键合有疏水性的链转移剂，因而在聚合介质中具有稳定的分散性，然后进行溶液聚合，实现单体在纳米粒子表面的可控限域聚合，形成PNIPAM包覆无机纳米粒子的核壳结构，获得具有温敏特性的多功能纳米复合材料。采用不同的无机物作为核材料，所得核壳结构将具有不同的功能，从而实现核壳纳米粒子在多个领域的应用，为无机/高分子纳米核壳结构的制备提供思路，对开发设计新型功能材料具有重要意义。

本项目的研究内容是金属及金属氧化物（如Fe3O4，Ag，CoO）的生长机制、结构及催化性能，分为三个部分，第一部分单分散超顺磁Fe3O4纳米粒子的形貌控制，形成机理及催化研究。通过调控种子溶剂热反应的条件，得到高质量的三角片和六边形FE3O4单分散纳米粒子，对纳米粒子的结构研究表明，两种粒子所有暴露晶面都是（111）面，它们都不是单晶，三角形粒子内部含有一个孪生晶面，六边形粒子的内部含有两个角度为60度的孪生晶面。孪生晶面的数目和取向是影响晶核生长模式和最终形貌的关键。研究表明，在极性不同的多种溶剂中所得四氧化三铁可以催化邻苯二胺和1,2-二苯基乙二酮生成喹喔啉，产率高达80%以上。本部分从能量角度对反常生长机理的解释，适用于其他面心立方晶体的生长，深化了对小尺度纳米晶体生长机制的理解，其优异的催化性能与溶剂无关，具有很大的应用前景。第二部分是醇溶性Ag/聚油酸复合微球的形成机制及结构研究。通过简单的一步法反应，硝酸银与油酸溶解后加热，油酸的羧基被银离子氧化后脱羧，形成非常稳定的自由基，这种高活性的自由基能够催化油酸分子链中间的双键聚合，得到链状聚合物分子。而银离子被还原后与油酸的羧基作用，银粒子尺度被控制在4-5纳米，并被链状聚油酸包裹起来，由于聚油酸上大量羧基的存在，所得Ag/聚油酸复合纳米微球在极性较强的乙醇中分散性良好，而在极性较弱的正己烷中沉淀。本部分的催化剂能引发低活性的双键聚合，对其形成，结构的研究对探索开发高效催化剂有重要意义。本项目的第三部分是研究了银离子对CoO生长的影响。在硝酸钴和油胺体系中，当质量为硝酸钴十分之一的硝酸银参与反应时，所得氧化钴为7-8纳米的立方块，当不使用硝酸银时，得到形貌不规则的CoO粒子。对比实验证明体系中银离子首先被还原，油胺的氧化产物（如氮氧化合物）与氧化钴晶核与{002}和{220}晶面有着更强的结合力，这类晶面在晶核生长过程中生长缓慢并最终保留，本部分为合成不同活性晶面的选择性调控提供了新颖的思路。