摘要
高介电常数材料是一种应用前景非常广泛的绝缘材料,它有着很好的储存电能和均匀电场的性能,在电子、电机和电缆行业中都有非常重要的应用。因此,提高电介质材料的介电常数具有重大意义。具有轻质、易加工、低成本和良好机械性能等优点的高介电常数聚合物基复合材料正受到世界广泛地关注。在现有的高介电常数聚合物基复合材料体系中,与两相的陶瓷/聚合物复合材料及导体/聚合物复合材料相比,导体/陶瓷/聚合物复合材料三相复合材料具有更高的介电常数。因此,开展导体/陶瓷/聚合物三相复合材料的研究具有重大的现实意义。
目前此类复合体系研究选用的导体材料多为金属、石墨及碳纳米管等无机材料,采用导电高分子聚苯胺(PANI)作为导体的研究较少。在复合体系的制备工艺方面,目前绝大多数研究采用的是传统的机械共混法及溶液共混法,而对于能将体系多相组分更好复合的原位聚合法制备工艺鲜见报道。
本论文采用原位聚合工艺,制备出一类导体(PANI)/陶瓷(BaTiO_3)二元复合材料前驱体,进而以综合性能优异的环氧树脂(Epoxy)作为基体,制备出导体(PANI)/陶瓷(CCTO)/聚合物(Epoxy)三相复合材料。分别研究了两类复合材料体系的微观形貌、电学性能、介电性能及热性能,从而为这类新型聚合物基复合材料的应用提供理论及实验基础。
通过原位聚合法制备了盐酸(HCl)及十二烷基苯磺酸酸(DBSA)掺杂体系的PANI(HCl)/BaTiO_3(K)及PANI(DBSA)/BaTiO_3(K)复合材料前驱体,二者均呈现PANI包覆BaTiO_3的核壳结构。对比研究了PANI(HCl)/BaTiO_3(K)及PANI(DBSA)/BaTiO_3(K)复合材料的热稳定性、电导率及介电性能。与PANI(HCl)/BaTiO_3(K)相比,PANI(DBSA)/BaTiO_3(K)复合材料的热稳定性明显提高,且具有更高的电导率和介电常数。
通过原位聚合法制备了PANI/CCTO/Epoxy复合材料,研究了Epoxy树脂、CCTO/Epoxy和PANI/CCTO/Epoxy复合体系的固化反应性。凝胶时间及DSC分析表明,CCTO及PANI的加入均对Epoxy的固化产生了阻碍作用,降低了体系的固化速率。SEM研究表明,填料CCTO及PANI分散性良好,与Epoxy基体有较好的相容性。通过DMA及TG手段研究了复合材料的热性能。DMA研究表明,随着CCTO及PANI/CCTO混合填料的加入,复合材料的Tg逐渐下降。TG研究显示,CCTO(K) 20%/Epoxy复合材料的热稳定性最优,PANI 5%/CCTO(K) 20%/Epoxy次之,二者较树脂基体Epoxy的耐热性能均有提高。通过宽频介电谱仪研究了复合材料的电导率及介电性能。研究表明,PANI m/CCTO(K) 20%/Epoxy复合材料的渗流阈值在0.06左右,复合材料的电导率、介电常数和介电损耗在渗流阈值附近显著突变。当PANI的体积分数低于渗流阈值时,复合材料的介电常数随频率的变化很小;当PANI的体积分数接近渗流阈值时,复合材料的介电常数随PANI含量的增大迅速增大,且随频率的增大迅速降低。在室温1KHz条件下,PANI m/CCTO(K) 20%/Epoxy复合材料在PANI体积分数为10%(m=10%)时得到最大介电常数220,相对于基体树脂Epoxy提高了62倍。?
High dielectric constant material is an insulation material with very broad application prospects in many fields such as electrical and cable industries, so it is important to enhance its dielectric constant. High dielectric constant polymeric matrix composites with advantages of light weight, easy processing, low cost and good mechanical properties, have caught worldwide attention. In the existing systems of high dielectric constant polymeric matrix composites, comparing to the two-phase ceramic/polymer composites and conductor/polymer composites, the three-phase conductor/ceramic/polymer composites have higher dielectric constant. Therefore, the study in the three-phase conductor/ceramic/polymer composite is of great practical significance.
At present the conductor of such complex systems are mostly inorganic materials such as metals, graphite and carbon nanotubes. It is rare to use conductive polymer as a conductor like conducting polyaniline (PANI). In aspects of preparing the composites, most of the studies took the traditional mechanical mixing and solution blending method, while the in-situ polymerization technique was rarely reported.
In this thesis, by the technique of in-situ polymerization, a series of conductor (PANI)/ceramic (BaTiO_3) binary composites were prepared as intermediates, then a conductor (PANI)/ceramic (CCTO)/polymer (Epoxy resin) three-phase composite was prepared taking epoxy resin (Epoxy) as substrate. The morphology, electrical properties, dielectric properties and thermal properties of the two series of composites were studied to provide theoretical and experimental basis for application of these new polymer matrix composites.
Two kinds of PANI/BaTiO_3 composites (coded as PANI(HCl)/BaTiO_3 and PANI(DBSA)/BaTiO_3) were synthesized by in-situ polymerization technique, in which PANI was doped with hydrochloride acid (HCl) or dodecylbenzene sulfonic acid (DBSA). The structure, morphology, thermal resistance, AC conductivity and dielectric ?properties of the composites were evaluated. Results show that the two kinds of composites have core-shell structure, in addition, comparing to PANI(HCl)/BaTiO_3, PANI(DBSA)/BaTiO_3 has better thermal stability, higher AC conductivity and dielectric constant.
A series of PANI/CCTO/Epoxy composites were prepared by in-situ polymerization. The curing behaviors of epoxy resin, CCTO/Epoxy and PANI/CCTO/Epoxy composites were studied. Gel time and DSC analyses show that the addition of CCTO and PANI/CCTO into epoxy reduces the curing rate of epoxy. SEM studies show that the CCTO and PANI fillers have good dispersion and compatibility with epoxy matrix. The thermal properties of the composites were studied by DMA and TG analysis. DMA analyses shows that the addition of CCTO and PANI/CCTO into epoxy slightly decreases the glass transition temperature (Tg). TG studies show CCTO(K) 20%/Epoxy has better thermal stability than PANI5%/CCTO(K) 20%/epoxy, and both of them have better thermal resistance than epoxy resin. AC conductivity and dielectric properties of the composite were studied by broadband dielectric spectroscopy. The results show that the percolation threshold of PANIm/CCTO(K)20%/Epoxy composites was about 0.06, and a significant mutation of AC conductivity, dielectric constant and loss appears near the percolation threshold. When the content of PANI is lower than the percolation threshold, the dielectric constant of the composites changes little with the increase of the test frequency, however, when the content of PANI is more than the percolation threshold, the dielectric constant of the composite increases rapidly with the increase of PANI content and decreases quickly with the increase of the test frequency. Under the condition of 1KHz at room temperature, PANI10%/CCTO(K)20%/Epoxy composite has the highest dielectric constant of 220, which increased 62 times than epoxy resin.
引文
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