【作者】 贺国文；

【导师】 李衡峰；

【作者基本信息】 中南大学 ， 材料物理与化学， 2012， 博士

【摘要】 聚酰亚胺(PI)具有其它高聚物无法比拟的优异的热、机械和电性能,在微电子领域和航空航天领域有着广泛的应用。随着材料的不断向高性能化、多功能化和低成本化方向发展,聚酰亚胺自身的一些缺点(如吸湿性和热膨胀系数较高)单纯的聚酰亚胺材料不能满足市场对其偏高(低)介电、低吸水率和良好的力学性能的要求。为了提高P1的应用性能,拓展聚酰亚胺材料的应用领域,以PI为基体的复合材料的开发与应用一直是学术界和工业界研究与开发的热点。本论文改善PI/无机纳米复合材料的制备方法,考察无机纳米粒子含量对复合材料的结构、形貌、性质的影响,可为PI/无机复合材料的制备和性能研究提供数据和理论参考。研究中,采用纳米粒子原位法或原位溶胶凝胶法,分别将二氧化硅(Si02)、多壁碳纳米管(MWNTs)与PI或含氟聚酰亚胺(FPI)复合制备聚酰亚胺基合材料,分别采用原位溶胶凝胶法和纳米粒子原位法制备了PI/TiO2和PI/TNTs复合材料,期望得到综合性能优异的复合材料,全面考察了各种复合材料的结构、形貌及其与性能的关系。论文采用纳米粒子原位法和原位溶胶凝胶法两种工艺制备了掺杂二氧化硅聚酰亚胺复合材料。研究发现采用原位溶胶凝胶法制备的复合薄膜相比纳米粒子原位法制备的材料具有更好的热稳定、透光性、电阻性和介电性能(介电常数可达3.0以下)、具有更大的储能模量(ε)和更高的玻璃化转变温度(Tg)。两种方法制备的复合薄膜的5wt%质量损失温度高于540℃,其热稳定性可很好满足它在众多器件中作为介电材料使用的要求。采用原位溶胶凝胶法制备了掺杂二氧化硅的FPI复合材料,该复合薄膜保持了纯FPI良好的热稳定性,复合薄膜的介电常数随二氧化硅含量的增加先略微增大再减小,在二氧化硅含量为10wt%时达到最大值,所有的复合薄膜拥有很低的介电常数。聚酰亚胺基体中加入MWNTs能保持很好的热稳定性。制备的PI/MWNTs和FPI/MWNTs纳米复合材料璃化转变温度分别在280℃和360℃以上,分解温度分别在550℃以上和约在500℃。碳纳米管本身良好的热稳定性和在基体中良好的相容性使得制备PI/MWNTs和FPI/MWNTs纳米复合材料具有很好的动态力学性能,其动态力学性能随着碳纳米管含量的增大而增强,50℃时MWNTs含量为10wt%的PI复合材料的储能模量为2.03Gpa,较纯PI提高了23.1%。PI和FPI的介电常数都随着掺杂碳纳米管含量的增大而增加。在1MHz PI中加入10wt%的碳纳米管时其介电常数为66.7,是纯PI的18.6倍,说明少量的加入量就可使材料的介电性能有很大的提高。含碳纳米管聚酰亚胺基纳米复合材料是一种具有良好热学和动态力学性能的高介电材料。在PI/TiO2和PI/TNTs两种复合薄膜中的无机相以无定型的状态均匀分散在PI基体中,但其透光性有所下降。两种复合薄膜在有无紫外光照射下具有不同的吸水趋势。在无紫外光照射下复合薄膜的吸水率随着TiO2含量的增大而减少,TiO2含量为20wt%时复合薄膜相比纯PI薄膜可降低吸湿水量0.3个百分点。复合薄膜在有紫外光(λ=365nm)照射下的吸水率随着TiO2的质量分数的增大而增大。PI/TNTs有与PI/TiO2同样的吸水特性,并且在有无紫外光照射下PI/TNTs均比PI/TiO2较高的吸水率。在PI/TNTs复合材料中TNTs由于外壁大量的羟基的作用使其与基体相互交联起来,具有较PI/TiO2更优异的热学和力学性能。TNTs质量分数为3%的复合薄膜的5%失重温度达到了535.4℃,较纯PI提高了64.2℃。TiO2和TNTs对复合薄膜的导电性影响比较小,复合膜的电阻率相比纯P1只下降了3个数量级。复合膜的介电常数也只得到了略微的提高,但复合膜的介电常数具有一定的紫外响应性。在波长365nm的紫外光照射下其介电常数,尤其是PI/TNTs薄膜,得到了一定的升高。更多还原

【Abstract】 Polyimides (PI) are widely used in the fileld of microelectronics and aerospace industry because of their favorable electric and mechanical properties, superior thermal stability and high strength that can not be compared by other polymer materials. With the materials continuously developing towards performance-enhancing multi functions and cost degradation, pure PI with some shortcomings of its own (such as moisture absorption and thermal expansion coefficient is higher) does not meet market requirement of low water absorption, slightly higher (or lower) dielectric constant and good mechanical properties. In order to improve application performance and expand the applications of polyimide materials, the PI matrix composites for the development and application in academic and industry has been a hot research focus. The purpose of this paper is to improve the preparation method of PI/inorganic nanocomposites. In this paper, the structure, morphology and properties of the composites influenced by the levels of inorganic nanoparticles were investigated. It shoule offer reference for prepare and properties study of PI/inorganic composites.In this paper, the methods of in situ polymerization with nanoparticle and in situ prepared by sol-gel process have been adopted to prepared composites of PI/SiO2, FPI/SiO2, PI/MWNTS, FPI/MWNTs, PI/TiO2and PI/TNTs. The relationship between properties of resulting materials and their structure, morphology have been further studied.In this paper, PI/SiO2nanocomposites were prepared by two methods, i.e., in situ prepared with nanopartocle and in situ prepared by sol-gel process. Study results indicated that composite film in situ prepared by sol-gel process,compareing to method of in situ prepared with nanoparticle, had better thermal stability, light transmittance, resistance and dielectric properties (dielectric constant less than3.0), higher storage modulus(ε) and glass transition temperature(Tg).5wt%mass loss temperature of composite thin films prepared by two methods all above540℃, this can be good to meet requirements of materials used as a dielectric material in nurmuous devices.FPI/SiO2composites in situ prepared by sol-gel process. The composite films maintained good thermal stability, and the water absorption rate decreased with the incorporation of silica nanoparticles increasing. The dielectric constants of composite films increased and then slightly decreased with the increased of silica contents, reaching to maximum when the content of silica reached to10wt%. All the composite films beared low dielectric constants.Other two PI composites, PI/MWNTs and FPI/MWNTs, successfully prepared by two-step method. The storage modulus and Tg continuously increased with increasing of MWNTs level. Tg of PI/MWNTs and FPI/MWNTs composites were above280℃and360℃, respectively, and decomposition temperature (Td), above550℃and about500℃. Because of MWNTs itself has excellent thermal stability and after modified hold good compatibility with PI matrix,PI/MWNTs possesed favorable dynamic mechanical properties. The dynamic mechanical properties improved with increasing of the mass fraction of MWNTs. The value of storage modulus was2.03GPa at50℃when the fraction of MWNTs was10wt%. Compared with that of pure PI, the storage modulus increased23.1%. The dielectric properties enhanced sharply with the increasing of mass fraction of MWNTs. For the nanocomposites containing10wt%of MWNTs, the dielectric constant reached to66.7at1MHz, which came up to18.6times of3.6for pure polyimide, indicating the dielectric of PI composites can be increased greatly by adding small amount of MWNT. Therefore, the PI/MWNTs is a kind of nanocomposite material with favorable properties of thermal properties, dynamic mechanical properties, dielectric properties.PI/TiO2and PI/TNTs films were prepared. The inorganic reinforcing phase TiO2or TNTs dispersed in the PI matrix homogeneously as amorphous state which caused transmittance of composite films decreased. The water absorption rate of two types of composite films had different trends with or without irradiation of UV. Water absorption rate of PI composite films decreased with increasing TiO2content without UV irradiation. Water absorption rate of the20wt% TiO2/PI film decreaed0.3percentage points compared to that of pure PI film, water absorption rate increased with the increase of TiO2content with UV irradiation (λ=365nm). PI/TNTs composite films had the same water absorption feature with PI/TiO2, and PI/TNTs had higher water absorption than PI/TiO2with or without UV irradiation.Massive Hydroxy (-OH) existed on exine of TNTs can act with matrix PI, then crosslinking between them was produced. Compered with PI/TiO2, PI/TNTs composites had better properties of thermal and mechanical properties. Temperature of5%weight loss of PI composite film with3wt%TNTs reched to535.4℃, increasing64.2℃compared to that of pure PI. Effect of TNTs and TiO2on the conductivity of composite film was relatively little.Compared to pure PI, the resistivities of composite films fell by only3orders of magnitude. Dielectric constants of the composite films had been only slightly improved but had a responsiveness to the UV. Under UV irradiation with a wavelength of365nm the dielectric constant of composite film, especially in PI/TNTs film, had a certain increase.更多还原