【作者】 徐平；

【导师】 韩喜江；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2010， 博士

【摘要】 导电聚合物及其复合材料在抗静电材料、电磁屏蔽材料、人工肌肉、二极管和晶体管等领域具有重要的应用价值,而且发现导电聚合物可以化学还原比其还原电位高的金属离子。本论文基于聚苯胺(PANI)和聚吡咯(PPy),对导电聚合物纳米纤维和薄膜材料上纳米金属的可控生长及分子检测性能、磁性导电聚合物复合材料的制备及其电磁吸收性能进行了研究。采用表面活性剂辅助化学氧化聚合方法制备了PANI、PPy和PANI-PPy一维纳米纤维材料。研究表明,PPy纳米球和纳米纤维的光谱性能基本一致,但两者具有依赖于形貌的电化学性能:PPy纳米球的电化学过程受半无限扩散控制,而PPy纳米纤维的电化学过程受阻挡层扩散控制。PANI-PPy共聚材料的化学成分对其性能的影响体现在:含有较多PANI或PPy的共聚材料具有类似于单一聚合物(PANI或PPy)的物理化学性能,而含有等量PANI和PPy的共聚材料表现出特有的性能。对导电聚合物纳米纤维化学还原制备金属纳米粒子的研究发现,不同的种类、形貌和掺杂剂使导电聚合物具有不同的还原电位和表面性质,使还原得到的金属纳米粒子具有不同的形貌和粒径。将PANI材料制备成薄膜,探讨了不同的掺杂剂、薄膜种类(多孔膜和密实膜)、导电类添加剂、外加电场等工艺参数对薄膜上纳米金属成核和生长的影响。不同的掺杂剂和薄膜种类使薄膜具有不同的化学性质和表面性质,可以生长不同的金属结构。在PANI多孔膜中加入导电类添加剂(石墨或碳纳米管)可以提高多孔膜表面的掺杂均一性,使其表面生长均匀的金属纳米粒子,并使多孔膜的导电性增强。外加电场可以改变多孔膜上Ag的成核和生长机理,产生一个由树枝状、花状和微球状Ag组成的梯度结构,其机理是电场作用下多孔膜表面Ag+的移动是纵向扩散和横向电场驱动的协同效应,而不加电场时Ag+的移动仅受扩散动力学控制。多孔膜上树枝状、花状和微球状Ag都具有较强的表面增强拉曼光谱(SERS)性能。PANI多孔膜上预先构造的纳米Au层和掺杂剂对均匀三维纳米片状Ag结构的形成至关重要,这种Au-Ag复合金属结构整个表面都具有均匀的SERS信号,检测灵敏度达到10 ppm,可以应用于化学和生物分子的检测。柠檬酸分子吸附在Au核或Ag核上对后续生长的Ag纳米粒子自组装成片状结构具有导向作用,这一认识实现了未掺杂PANI多孔膜上均匀纳米Ag片状结构的构造。基于这种机理构造的由片状纳米Ag自组装而成的线状结构对20 ppm三聚氰胺具有很好的SERS响应。仅在柠檬酸掺杂的PANI密实膜上可以生长得到Ag纳米线,而且在同一PANI密实膜上生长有不同结构的Ag纳米线。在-0.05~+0.05 V及0~+4 V电位区间内测试了Ag纳米线的电学稳定性,单一Ag纳米线的熔断电压位于1.5 V左右。电迁移和表面扩散是造成Ag纳米线在电性能测试中熔断或发生形貌改变的主要原因。由Ag纳米粒子组装而成的Ag纳米线存在生长缺陷,电导率要比光滑Ag纳米线低。采用反相微乳液法合成了六角片状纳米钡铁氧体(BaFe12O19),确定了烧结工艺、Fe/Ba比例。以纳米BaFe12O19和Ni为磁性核,采用原位化学氧化聚合法制备了BaFe12O19-PANI、BaFe12O19-PPy、Ni-PPy磁性导电聚合物复合材料,发现无机材料和导电聚合物之间没有明显的化学作用,无机材料只是作为有机单体聚合时的成核中心。复合材料的导电性、磁性、电磁吸收性能可以通过调节无机相和有机相的相对比例而进行调控。复合材料电磁吸收性能结合了磁性材料的磁损耗和导电聚合物的介电损耗,而且无机磁性材料表面包覆导电聚合物后其复磁导率和复介电常数可以得到调节,符合传输线理论中对材料阻抗与自由空间阻抗匹配的要求。经过调控制备的磁性导电聚合物复合材料在2~18 GHz频率范围内具有增强的电磁吸收性能,并可调节吸收频带。更多还原

【Abstract】 Conducting polymers and their composites have significant applications in electrostatic materials, electromagnetic shielding materials, artificial muscles, diodes, transistors, etc. It has been recognized that a metal ion having a higher reduction potential than that of a conducting polymer can be chemically reduced by the conducting polymer. Based on polyaniline (PANI) and polypyrrole (PPy), controlled growth and molecule detection properties of metal nanostructures reduced by using conducting polymer nanofibers, membranes and films, as well as prepration and electromagnetic properties of magnetic conducting polymer composites were studied in this thesis.One-dimensional (1D) PANI, PPy and PANI-PPy copolymer nanofibers are prepared by a surfactant-assisted chemical oxidative polymerization. Though spectroscopic properties of PPy nanospheres and nanofibers are almost identical, the electrochemical responses are morphology-dependent: electrochemical process of PPy nanospheres is controlled by semi-infinite diffusion, while that of PPy nanofibers is dominated by barrier diffusion. Effect of chemical composition on the properties of PANI-PPy copolymers can be described as: PANI-PPy nanofibers synthesized with an excess of either PANI or PPy show similar physico-chemical characteristics as the individual homopolymers, whereas nanofibers from an equimolar mixture of An and Py display unique properties. Preparation of metal nanostructures from chemical reduction of metal ions by conducting polymer nanofibers is also discussed. Conducting polymers with different catagories, morphologies and dopants have various reduction potentials and surface properties, which can be accounted for the yield of metal nanoparticles with different morphologies and sizes.PANI porous membranes and dense films are fabricated, and effects of technique parameters such as dopant, conductive additive, external electric field on the nucleation and growth of metal nanostructures are discussed. Different dopants render PANI porous membranes or dense films with different chemical natures and surface properties, leading to different metal structures grown on PANI membranes or films. Addition of conductive additives (graphite or carbon nanotube) in PANI porous membranes can increase the conductivity of the membrane and improve the doping inhomogeneity of the membrane surface, thus homogeneous metal nanoparticles can be produced. Application of an external electric field to the P-G or P-CNT porous membranes can alter the nucleation and growth mechanism of Ag, resulting in a Ag gradient structure comprised of dendrites, flowers and microspheres. It is believed that the formation of such silver gradient is a synergetic consequence of a vertical diffusion and a lateral electrokinetic flow in the field-assisted model when Ag+ ions move to the membrane surface and are reduced by PANI. While in the absence of an electric field, the movement of Ag+ ions is dominated by a simple diffusion process. It is revealed that the Ag dendrites, flowers and microspheres all possess strong surface enhanced Raman spectroscopy (SERS) properties.Both the pre-fabricated gold nanolayer and chemical nature of the PANI porous membrane play pivotal roles in the formation of homogeneous 3D Ag nanosheet structures. The fabricated Au-Ag hybrid structures show strong and uniform SERS enhancement of the absorbed molecules over the whole surface, with a detection sensitivity of 10 ppm, indicating a promise for sensitive detection of chemical and biological analytes. It is revealed that citric acid absorbed onto the pre-fabricated Au or Ag nanoparticles directs the self-assembly of subsequent grown Ag nanoaprticles into nanosheet structures. This recognition makes the fabrication of homogeneous Ag nanosheet structures on undoped PANI porous membranes become available. Moreover, based on the above mechanism, a wire structure consisting of assembled Ag nanosheets is also successfully fabricated, which shows promising SERS recognition of 20 ppm melamine molecules.Current study reveals that Ag nanowires can only be grown on citric acid doped PANI dense films. Ag nanowires with a wide range of morphologies and sizes can be obtained on one single PANI film. Electrical stability of the Ag nanowires is tested in the voltage range of -0.05~+0.05 V and 0~+4 V respectively, and a meltdown voltage of about 1.5 V is determined. Electromigration and surface diffusion can both be accounted for the meltdown or morphology change of the Ag nanowires during the electrical measurements. The nanowires comprised of self-assembled Ag nanoparticles usually have lower electrical conductivities than those with smooth surfaces, due to the presence of growth defects.Hexagonal barium ferrite (BaFe12O19) nanoparticles have been prepared from a reverse microemulsion technique, and optimum sintering condition and Fe/Ba ratio are determined. Using BaFe12O19 nanoparticles and nickel powder as magnetic cores, BaFe12O19-PANI, BaFe12O19-PPy and Ni-PPy composites are prepared through an in situ chemical oxidative polymerization method. There is no obvious chemical interaction between the conducting polymer and inorganic phase, where the inorganic phase simply plays a role of nucleation center during the polymeri- zation of organic monomers. Electrical conductivities, magnetic properties and electromagnetic properties of the composites can be modulated by controlling the relative content of the inorganic phase and organic phase. Electromagnetic properties of the composites result from a combination of magnetic loss of magnetic materials and dielectric loss of conducting polymers. Complex permeability and permittivity of the composites can be tuned by coating the magnetic materials with conducting polymers, leading to a better impedance matching between the compistes and free space as required according to the transmission line theory. Magnetic conducting polymer composites show promising electromagnetic absorption properties in the frequency range of 2~18 GHz, and the absorption band can be finely tuned.更多还原