【作者】 陈倩；

【导师】 杜丕一；

【作者基本信息】 浙江大学 ， 材料学， 2007， 硕士

【摘要】 随着电力电子设备发展的日新月异，高储能电容器向多功能，小型化的方向发展。高介电常数的柔性聚合物基电介质复合材料在电子工业领域可能有广泛的应用前景，它可以被用来制作具有任意形状的多层片式电容器，因此提高电介质材料的介电常数具有非常重要的意义。根据渗流理论，对于导体/聚合物复合材料，当导体的体积分数逼近渗流阈值时，复合材料的介电常数将发生非线性变化且大幅提高。因此，渗流理论对于制备高介电常数聚合物基复合材料是十分有意义的。本文利用渗流理论，研究了以聚偏氟乙烯（PVDF）柔性聚合物与聚偏氟乙烯/钛酸钡为基体，成本低廉的乙炔黑粉末作为填料制备的复合厚膜的微结构和介电性能。以DMF为溶剂，采用浸渍提拉法制备了PVDF厚膜，PVDF/AB复合厚膜，PVDF/BT复合厚膜，PVDF/BT/AB复合厚膜，利用XRD和SEM等手段对材料的物相组成和微结构进行了分析，利用阻抗分析仪等仪器对材料的介电性能进行了研究。研究结果表明，在较低温度下（60℃），由于基板的诱导作用，得到的PVDF厚膜呈β相结构，其介电常数比较高。热处理时间对其晶相的形成，晶相的含量和介电性能均无影响。当乙炔黑的体积分数在f=1.3％附近，亦即处于渗流阈值附近时，PVDF/AB复合厚膜呈现显著的渗流效应，材料的介电常数大幅度提高，介电常数达到56左右，是PVDF基体的7～8倍。在复合体系中，由于乙炔黑具有长条形链状结构，比球形颗粒更易相互连接形成渗流通路，其渗流阈值明显低于典型渗流阈值。此超低的渗流阈值，即极少的无机粒子添加量即可保证复合厚膜良好的弹性和加工性能。此外，PVDF/AB复合厚膜的介电损耗在渗流阈值附近保持在0.15以下可能是由于复合体系中的非晶相的存在。在低频下，PVDF/AB复合厚膜的介电常数并不随着频率的变化而变化，这表明了在复合体系中并不存在空间电荷极化效应。研究结果还表明，当钛酸钡体积分数等于30％，PVDF/BaTiO₃（BT）复合厚膜介电常数最大。当BaTiO₃体积分数小于30％，复合材料的介电常数随BaTiO₃体积分数的变化趋势与Maxwell-Garnett方程计算出的理论值相符；而当BaTiO₃体积分数大于30％时，复合材料的介电常数随BaTiO₃体积分数增加而下降，与Bruggemant方程计算理论值不相符。这是因为随着BT的含量的增加，PVDF不能很好结晶，复合厚膜的微观结构也出现较大孔洞，材料彻底失去弹性。在渗流阈值(f_AB=3.3％)附近，PVDF/BT(f_BT=30％)/AB复合厚膜的介电常数达到了652，是PVDF/BT基体的40多倍，是PVDF基体的90多倍。使用硅烷偶联剂KH550对BaTiO₃粒子表面处理，能有效解决BaTiO₃粒子在前驱体悬浊液中的沉降导致复合厚膜中BaTiO₃粒子分布不均和不稳定的问题，一定程度上改善了纳米BaTiO₃粒子的团聚现象，可以提高PVDF/BT/AB复合厚膜的介电常数。更多还原

【Abstract】 With fast development of the electronic equipment, high-performance capacitors call for smaller size and multi-function. And the flexible composites with a high dielectric constant have a great future in the electronic industry field. The composites may be used to prepare a shape-bend mutilayer chip capacitors. Therefore, it is very significant for improving the dielectric constant of the composites.According to the percolation theory, as for the conductor/polymer composites, when the volume fraction of the conductor is close to the percolation threshold, the dielectric constant of such material will undergo a nonlinear transition and increases sharply. Therefore, it is meaningful to use the percolation theory to prepare the material with high dielectric constant.The microstructure and dielectric constant of composite films were studied, which were made of polymer matrix, such as polyvinylene fluoride （PVDF） or PVDF/BaTiO₃ （BT） , and cheap conductor filler, such as acetylene black （AB）. PVDF/AB composite film, PVDF/BaTiO₃ composite film, and PVDF/ BaTiO₃/AB composite film were prepared by using dip-coating method with N,N-dimethyllformamide （DMF） as solvent. Phase structures and morphologies of the composite films were characterized by X-ray diffraction and Field Emission-Scan Electron Microscopy （FE-SEM） respectively. The dielectric properties of samples were measured using Agilent 4294A precision impedance analyzer in the frequency range of 100 Hz -10 MHz at room temperature.The experimental results reveal that, as for PVDF films, at lower heat treatment temperature （60°C） ,β-PVDF forms, and its dielectric constant is relatively higher; while, at higher heat treatment temperature （100°C）, α-PVDF forms, and its dielectric constant is relatively lower. And the time for heat treatment has no effect on the crystalline phase formation, crystalline content and dielectric property of the PVDF film. As for PVDF/AB composite film, when AB volume fraction is close to the percolation threshold （f=1.3%）, the dielectric constant of PVDF/AB composite film reach about 56, which is 7-8 times higher than that of PVDF film. Due to the longchain structure of AB particles, the percolation threshold （f_c=1.3%） of PVDF/AB film is much lower than the typical one （f_c=16%）, which ensures the excellent flexibility and processing property. In addition, due to the existence of amorphous state, the dielectric loss of PVDF/AB film is below 0.15, when AB volume fraction is close to the percolation threshold. The fact that, dielectric constant of PVDF/AB film is independent of low frequency, shows no space charge polarization occurs.The experimental results also show that, when BaTiO₃ volume fraction is 30%, the dielectric constant of PVDF/ BaTiO₃ composite film is highest. When BaTiO₃ volume fraction is lower than 30%, the variation of dielectric constant of PVDF/ BaTiO₃ film with BaTiO₃ volume fraction is in good agreement with the data calculated by Maxwell-Garrett equation; when BaTiO₃ volume fraction is higher than 30%, the variation of dielectric constant of PVDF/BaTiO₃ film with BaTiO₃ volume fraction is not in agreement with the data calculated by Bruggemant equation. This is because when BaTiO₃ volume fraction is higher than 50%, the crystallinity of PVDF is low and the film quality deceases. When AB volume fraction is close to the percolation threshold （f=3.3%）, the dielectric constant of PVDF/BaTiO₃/AB composite film reach about 652, which is 90 times higher than that of PVDF film and 40 times higher than that of PVDF/BT film.The problem of BaTiO₃ precipitation is solved by surface treating of BT particles using KH550. This method can not only solve the BT aggregation problem, but also enhance the dielectric constant of PVDF/BT/AB composite films.更多还原