【作者】 江美娟；

【导师】 党智敏； 白晋波；

【作者基本信息】 北京化工大学 ， 材料学， 2009， 博士

【摘要】 压敏导电复合材料电阻随外加压力的变化而变化(压阻性能),可作为压力传感器材料。压力传感器材料应具有较高的压敏强度、较低压缩永久变形、性能稳定且弹性模量与其接触材料相匹配。然而,在过去的发展过程中,受填料和加工工艺的限制,压敏材料可控性低,重复性较差,发展较缓。同时,导电填料填充聚合物复合材料是一类新型高介电材料,尽管在过去的一段时间,人们对这类复合材料的介电行为和逾渗现象进行了一定的研究,然而对于其在交变电场下的极化规律以及电导机理仍然不是很清楚。本文选择性能优异的多壁碳纳米管作为功能填料,在对其改性的基础上,采用湿法和三辊研磨机制备了碳纳米管/硅橡胶复合材料,对其导电、介电和压阻性能及影响因素作了详细研究。通过对碳纳米管表面修饰研究发现,硅烷偶联剂KH550是碳纳米管/硅橡胶复合材料一类简单有效的改性剂,可直接与原始碳纳米管表面存在的有机基团发生化学反应,维持了碳纳米管原有的性能,提高了碳纳米管与硅橡胶之间的结合力,使碳管较均匀的分散在基体中,提高了复合材料的机械性能。同时,采用三辊研磨机制备得到填料完全分散的改性碳纳米管/硅橡胶复合材料。本文对碳纳米管/硅橡胶复合材料的逾渗情况作了详细研究,考察了复合材料导电性能的影响因素,总结了导电性和填料分散之间的关系。研究发现,复合材料的渗流阈值较小,仅为1.0 vol.%,这保证了复合材料较好的弹性和性能稳定性。但相对结晶高聚物基体复合材料,碳纳米管/硅橡胶基复合材料的渗流阈值较大。并且由于碳管在聚合物基体中弯曲分布,其有效长径比降低,导致其渗流阈值高于理论估算值。同时,碳管表面被基体包裹,复合材料中主要为隧道和跃迁导电。在一定范围内,电导率随着温度的增大而增大。较强的界面作用在提高碳纳米管分散的同时也阻碍了电子的传导。本文通过对交流阻抗谱图的分析,建立了复合材料等效电路,对其弛豫机制和交流导电机理进行了比较详细的分析。研究发现,两个并联的电阻-电容电路串联构成了复合材料的等效电路。在低频时,复合材料电导率不随频率变化而变化;中高频时,由于电容和界面极化松弛作用,电导率随频率的增大而增大。当复合材料电导率达到一定程度时,材料具有电感性,在高频时,电导率随频率的增大而减小。同时,复合材料介电常数随频率变化曲线可分为三部分,在低频下发生低频介电弥散现象(LFD),介电常数随频率成指数性变化;中频率阶段,极化主要为碳纳米管和基体形成的界面局域电荷跃迁,类似于偶极子,介电常数对频率的依赖性较低;高频主要是碳纳米管本身电子云的极化。中频区域介电常数的大小取决于两个方面,一方面为复合材料中局域电荷的数量,另一方面为界面势垒能的大小。因为在一定范围内随着碳纳米管含量的增大,复合材料内部界面势垒能的高低,局域电荷和导电网络同时增多,导致其介电常数和电导率都增大。但当碳纳米管含量继续增大,大多数碳管参与形成导电网络,局域电荷变少,介电常数下降。以上导电和介电理论的提出为制备高导电、高介电复合材料提供了理论基础。最后,本文对复合材料压阻性能的机理和影响因素作了详细考察。研究发现,碳纳米管/硅橡胶复合材料的电阻随着压力的增大而增大,而且在一定压力范围内电阻的对数与压力呈良好的线性关系,属于一种新型压敏材料。压阻性能与复合材料中填料的含量直接有关,当填料含量较多时,粒子之间的平均距离较小,压力的作用可使粒子之间相互接触,从而电导率增大;但当填料含量比较少时,粒子之间的平均距离较大,压力主要破坏已经形成的导电网络,而难以促使新的导电渠道形成。对于碳纳米管/硅橡胶复合材料,较少量的碳管首尾相接形成了导电网络,致使碳管之间的平均距离较大,因而复合材料电阻随着压力的增大而增大。通过对压阻性能影响因素研究,本文制备了线形可控、压敏强度高和重复性强的压敏导电复合材料。更多还原

【Abstract】 The electrical conductive rubber-based composites can be used as pressure-sensors in practice. However, in the past, the pressure-sensitive materials developed slowly due to the limitation of fillers and the preparation technology. Meantime, this kind of materials is a new type of high-dielectric constant materials. The law of polarization and the mechanism of electric conductance under the alternating current (AC) field are still uncertain, although dielectric performance and percolation effect were studied in the past years.In this paper, multi-walled carbon nanotubes(MWNT) with excellent properties are used as the functional fillers, their composites with silicone rubber(SR) were prepared by wet method and three roll mills mixing method and the electrical conductive, dielectric and resistance-pressure properties of composites were investigated.It is found that coupling agent KH550 was a kind of simple and effective modifier, which can improve the interfacial interaction, the dispersion and the mechanical properties of composites. Meanwhile, the dispersion of the modified MWNT/SR composites prepared by three roll mills is completely homogenous.The percolation effect and the factors of electrical conduction were studied. It is found that the percolation threshold of MWNT/SR composites is small and only 1.0 vol. %, which guarantees the good elasticity and stabilization of composites. Meanwhile, the relationship between dispersion and electrical conductive properties was explored and the conduction mechanism is summed up.According to the analysis of the alternating current impedance spectra, the equivalent circuits of MWNT/SR composites are built and the law of polarization and mechanism of electric conductance under the alternating current (AC) field were explored. It is founded the resistance of MWNT/SR composites increases with the applied pressure, which is different with the traditional pressure-sensitive conductive materials. The mechanism and factors of pressure-sensitive properties are investigated. It is concluded that the MWNT/SR composites have high resistance-pressure sensitivity, good controllability and stable property as force-sensitive element, which are potential to be used a novel type of pressure sensor.更多还原