【作者】 王杨勇；

【导师】 井新利；

【作者基本信息】 西安交通大学 ， 化学工程， 2007， 博士

【摘要】 聚苯胺(PANI)纳米纤维的合成方法和应用是近年来颇受关注的研究热点。PANI的原料易得、合成方法简单、电导率可调、环境稳定性好,是目前研究最为深入、应用前景广阔的本征型导电高分子之一。PANI纳米纤维兼具有机导体和低维纳米结构的特点,可应用于分子导线、传感器、能量存储和场发射等领域。PANI纳米纤维的出现在一定程度上克服了PANI较差的加工性,极大地促进了PANI的广泛应用。本论文提出了一种适合规模化制备PANI纳米纤维的新方法,即在PANI的化学氧化聚合过程中引入超声波,方便地实现PANI纳米纤维的合成和结构调控。论文比较了超声波辐射聚合和界面聚合两种PANI纳米纤维的制备方法,探讨了PANI纳米纤维的形成机理,研究了PANI纳米纤维在导电透明薄膜和电磁干扰(EMI)屏蔽涂料方面的应用。论文取得以下创新性研究成果。1.在常规PANI的化学氧化聚合过程中,以超声波辐射代替机械搅拌,实现了无模板制备PANI纳米纤维,合成过程具有方便、简单和产率高(59%)等特点。论文通过反应物的二次滴加过程证实了超声波能够有效的抑制PANI纳米纤维的生长和团聚。研究还发现,超声波聚合速率加快,但产物分子量和电导率降低。反应体系中,较低的过硫酸铵(APS)/苯胺摩尔比(≤1.0)有利于制备高品质、直径约50nm的PANI纳米纤维;较高APS/苯胺摩尔比(2.5)则会得到PANI无规颗粒和直径约100nm PANI纳米纤维的混合物。2.通过改变APS和苯胺溶液的混和方式进一步证实超声波对初始PANI纳米纤维的生长和团聚的抑制作用。在普通直接混合聚合中,只能在较低苯胺浓度(≤0.05 M)下得到PANI纳米纤维;随着聚合体系中苯胺浓度的提高(如0.10 M),产物转变为直径约100nm的纤维团聚体和无规颗粒的混合物;超声波辐射可以抵消苯胺浓度提高对PANI纳米纤维形成带来的负面效果,在较高苯胺浓度下也可以得到PANI纳米纤维。反滴加方式下,随着反应的进行,磁力搅拌体系中产物逐渐从起始的初始PANI纳米纤维演变成为层片状PANI和PANI纳米纤维团聚体的混合物,而在超声波辐射体系中,产物始终是PANI纳米纤维。3.在超声波作用下,以双氧水为氧化剂合成的PANI纳米纤维更长(约300～1000nm)、更规整。在机械搅拌作用下,反应体系的诱导期较长,反应过程近似为一种直接混合聚合,反应初期,产物是PANI纳米纤维;随反应进行,产物转变为无规颗粒和直径较大、表面粗糙的PANI纤维的团聚体。在超声波辐射条件下,反应诱导期显著缩短,表明反应速率的提高,所得PANI纳米纤维形貌更加均匀、长径比更高,但产率有所降低。4.界面聚合中互不相容的两相界面的存在并不能完全抑制和阻止初始PANI纳米纤维的二次生长,体系中单体浓度才是决定PANI形貌的重要因素。此外,搅拌速率也对产物形貌有一定影响。5.化学氧化聚合中,在机械搅拌或静置条件下,若能在PANI纳米纤维生成后切断其与单体及氧化剂的接触(如界面聚合、低浓度下的直接混合聚合等),就可以直接获得PANI纳米纤维。反之,这些PANI纳米纤维的存在会进一步催化与其接触的苯胺分子的聚合,致使PANI纳米纤维的进一步长大,并最终转变为PANI无规颗粒(如常规的PANI合成过程)。在超声辐射作用下,即使在已有PANI纳米纤维和更多苯胺单体的共存下,体系中主要发生的还是PANI纳米纤维的生成,即超声波可以抑制PANI纳米纤维的二次生长和团聚。6.超声波作用下得到的PANI纳米纤维和常规PANI无规颗粒具有相同的化学结构和结晶程度,PANI分子链在PANI纳米纤维内部呈无规分布状。氧化剂的改变不会影响PANI纳米纤维的FTIR和XRD特征、分散性以及电导率,在以H2O2为氧化剂所得的PANI纳米纤维中只有头-尾结构的PANI分子,这与以APS为氧化剂合成的PANI纳米纤维有所不同。PANI纳米纤维具有良好的分散性,可以方便的分散在水、乙醇、甲基异丁基甲酮(MIBK)等溶剂中。7.采用超声波辐射聚合方法,在硫酸体系中合成了硫酸掺杂的PANI纳米纤维。以此PANI纳米纤维为填料,仅采用机械搅拌和超声波振荡处理,分别制备了PANI纳米纤维在聚甲基丙烯酸甲酯(PMMA)和聚丙烯酸树脂(PA)的MIBK溶液中的分散液,并分别以此分散液制备了导电透明PMMA/PANI纳米纤维复合薄膜和PA/PANI纳米纤维EMI屏蔽涂层。该薄膜和涂层制备过程具有方法简单、能耗低等特点,有利于工业化制备,是很有前景的PANI加工途径,并有助于它的广泛应用。更多还原

【Abstract】 Both the discovery of new approaches for synthesizing polyaniline (PANI) nanofibers and the demonstration of potential applications of the nano-materials have been the research focuses in recent years. PANI is one of the most intensively investigated intrinsically conducting polymers because of its low cost, easy synthesis, tunable conductivity, environmental stability and many promising applications. PANI nanofibers exhibit the advantages of both the organic conductors and low-dimensional nano-structures, demonstrating potential applications in the fields of molecular conducting wires, actuators, energy storage and field emitting and so on. Furthermore, PANI nanofibers solved, to some extent, the problem of intractability of PANI, facilitating the wider applications of PANI. In this dissertation, a novel template free method with good scalability was put forward to prepare PANI nanofibers, i.e. by exerting ultrasonic irradiation in the chemical oxidative polymerization of aniline, PANI nanofibers with controlled structures were successfully prepared. The ultrasonic irradiation method was compared with the interfacial polymerization for preparation of PANI nanofibers, and the formation mechanism of PANI nanofibers was discussed. The applications of PANI nanofibers in the fields of transparent conductive films and electromagnetic interference (EMI) shielding were explored. All results and conclusions obtained are listed below.1. By simply replacing the mechanical stirring in the traditional PANI synthesis procedure with ultrasonic irradiation, PANI nanofibers were facilely prepared without use of any template, and a relatively higher yield of 59% was demonstrated. The effect of ultrasonic irradiation on preventing the growth and agglomeration of PANI nanofibers was confirmed by the secondary addition of the reagents. It was found that the polymerization rate of the ultrasonic irradiated system increased, but the molecular weight and conductivity of the polymer decreased. In the case of lower ammonium peroxydisulfate (APS)/aniline molar ratios (e.g.≤1.0), PANI nanofibers in diameters of 50nm with high quality were achieved, while in the case of higher APS/aniline molar ratios (e.g. 2.5), mixtures of PANI nanofibers in diameters of 100nm and micro-sized irregular PANI particles were obtained. 2. By changing the mixing manner of the solutions of APS and aniline, the effect of ultrasonic irradiation on preventing the growth and agglomeration of PANI nanofibers was confirmed further. With the conventional rapid mixing polymerization, PANI nanofibers can only be achieved at lower aniline concentrations (≤0.05 M), and aggregates of PANI nanofibers with diameters of 100nm mixed with irregular shaped PANI particles were formed at relatively higher aniline concentrations (e.g. 0.10M). However, with exertion of ultrasonic irradiation, the negative effect of higher aniline concentration on formation of PANI nanofibers was neutralized, and PANI nanofibers were also prepared easily at higher aniline concentration (e.g. 0.10M). With the solution of aniline added dropwise into that of APS, i.e. in the reverse addition manner, the primarily formed PANI nanofibers changed into mixtures of PANI nanofibers and laminas with continue of the polymerization under mechanical stirring, while under ultrasonic irradiation, PANI nanofibers were resulted for all the time.3. PANI nanofibers with higher lengths (ca. 300-1000nm) and purity were synthesized employing H2O2 instead of APS as the oxidant by the ultrasonic irradiation method. In the case of mechanical stirring, the induction period of the reaction was so long that the polymerization can be considered as a rapid mixing polymerization. Though PANI nanofibers were initially formed at early stages of polymerization, mixtures of irregular PANI particles and aggregates of PANI nanofibers with rough surfaces were resulted with progressing of the polymerization. In the case of ultrasonic irradiation, the induction period reduced greatly, indicating the increasing of the polymerization rate. The product exhibit more uniform morphology, higher aspect ratio, but slightly decreased polymer yield.4. The presence of an interface formed between two immiscible liquids was not able to depress and prevent completely the secondary growth of the primary PANI nanofibers in an interfacial polymerization, and the aniline concentration is the key factor that determines the morphology of PANI. Besides, the stirring speed had some effect on the morphology of the polymers.5. With mechanical stirring or no stirring during chemical oxidative polymerization, if the contact between aniline and the formed PANI nanofibers can be avoided (e.g., in the case of the interfacial polymerization, rapid mixing polymerization with lower aniline concentration, etc.), PANI nanofibers can be achieved in the final product. Whereas, the PANI nanofibers would catalyze further the polymerization of the aniline around them, leading to the growth of PANI nanofibers, and final product of irregular micro-sized PANI particles were obtained (e.g. the conventional prepared PANI). In the case of ultrasonic irradiation, although the PANI nanofibers co-existed with excess aniline molecules, what happened mainly were the transformation from PANI molecules to PANI nanofibers, but not the growth of PANI nanofibers, i.e., the ultrasonic irradiation prevented effectively the growth of PANI nanofibers, resulting in completely PANI nanofibers in the final product.6. The sonochemically prepared PANI nanofibers exhibited the same chemical and crystal structures as the traditionally prepared PANI irregular particles, with all the PANI molecules distributed randomly inside the PANI nanofibers. Variation of the oxidants had no influence on the Fourier transformed infrared (FTIR) spectra, X-ray diffraction (XRD) patterns, dispersibility and conductivity of the PANI nanofibers. While only head-to-tail structured PANI molecules were observed inside the PANI nanofibers prepared with H2O2 as oxidant, which is different from the product prepared with APS as oxidant. PANI nanofibers demonstrated good dispersibility and can be dispersed easily in a variety of solvents, such as water, ethanol, methyl isobutyl ketone (MIBK) and so on.7. Sulfuric acid doped PANI nanofibers were sonochemically prepared in a reaction medium of sulfuric acid. By dispersing the sulfuric acid doped PANI nanofibers in either the solution of poly (methyl methacrylate) (PMMA) or polyacrylate (PA) in MIBK with just mechanical stirring and ultrasonicating processing, transparent conductive PMMA/PANI nanofibers composite films or PA/PANI nanofibers electromagnetic interference (EMI) shielding coatings were prepared. Preparation of the PANI nanofibers based films or coatings is one of the most promising processing techniques owing to its easiness and low energy consuming characteristics, which is beneficial for practical application of PANI.更多还原