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【6h】 Thermal conductivity and multiferroics of electroactive polymers and polymer composites.

机译电活性聚合物和聚合物复合材料的热导率和多铁性。

【摘要】Electronically conducting polymers and electromechanical polymers are the two important branches of the cutting-edge electroactive polymers. They have shown significant impact on many modern technologies such as flat panel display, energy transport, energy conversion, sensors and actuators. To utilize conducting polymers in microelectronics, optoelectronics and thermoelectrics, it is necessary to have a comprehensive study of their thermal conductivity since thermal conductivity is a fundamental materials property that is particularly important and sometimes a determining factor of the device performance. For electromechanical polymers, larger piezoelectric effect will contribute to the improvement of magnetoelectric (ME) coupling efficiency in their multiferroic composites. This dissertation is devoted to characterizing electronically conducting polymers for their electrical and thermal conductivity, and developing new classes of electromechanical polymers and strain-mediated electromechanical polymer-based multiferroic ME composites.;Conducting polymers opened up new possibilities for devices combining novel electrical and thermal properties, but there has been limited understanding of the length-scale effect of the electrical and thermal conductivity, and the mechanism underlying the electricity and heat transport behavior. In this dissertation, the analytical model and experimental technique are presented to measure the in-plane thermal conductivity of polyaniline thin films. For camphorsulfonic acid doped polyaniline patterned on silicon oxide/silicon substrate using photolithography and reactive ion etching, the thermal conductivity of the film with thickness of 20 nm is measured to be 0.0406 W/m˙K, which significantly deviates from their bulk (> 0.26 W/m˙K). The size effect on thermal conductivity at this scale is attributed to the significant phonon boundary scattering. When the film goes up to 130 nm thick, the thermal conductivity increases to 0.166 W/m˙K, greatly affected by the phonon-phonon scattering and phonon boundary scattering. When the films are thicker than 130 nm, heat capacity also plays an important role in thermal conduction in polyaniline.;The same technique is extended to measure the electrical and thermal conductivity of 55 nm thick polyaniline thin films doped with different levels of camphorsulfonic acid. Results indicate that the effect of the doping level (camphorsulfonic acid/polyaniline ratio) is more pronounced on electrical conductivity than on thermal conductivity, thereby greatly affecting their ratio that determines the thermoelectric efficiency. At the 60% doping level, polyaniline thin film exhibits the maximum electrical and thermal conductivity due to the formation of mostly delocalized polaron structures. It is suggested that polarons are the charge carriers responsible for the electrical conduction, while phonons play a dominant role in the heat conduction in doped polyaniline thin films.;Multiferroic materials combine unusual elastic, magnetic and electric properties, and have promising applications in many areas, such as sensors, transducers and read/write memory devices. For strain-mediated multiferroic ME composites, their ME effect are generated as a product property of the piezoelectric phase and magnetostrictive phase. In this dissertation, new multiferroic composites are developed and presented. One of them is based on chain-end cross-linked ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE). With a low dc bias magnetic field, the ME coefficient of this composite is 17.7 V/cm Oe at non-resonance and 383 V/cm Oe at resonance, well above the reported ME voltage coefficient of polymer based ME composite in current literature.;ME composite based on poly(vinylidene fluoride-co-hexafluoropropylene) P(VDF-HFP) are also developed in this dissertation. Crystalline beta phase structure in P(VDF-HFP) is produced by uniaxially stretching of pre-melted and quenched films. ME voltage coefficient as a function of dc magnetic field at different poling fields is measured. It is found that there is a linear relationship between the ME voltage coefficient of the composite and the poling field. Moreover, an electric field-induced phase transition is observed in P(VDF-HFP), manifested by the evolution of a double hysteresis D-E loop at intermediate poling field to a single loop at high poling field. The double hysteresis loop is due to the antiferroelectric phase that will transform into the ferroelectric phase when poled at high electric field. It is also found that in antiferroelectric-like and ferroelectric P(VDF-HFP), there is a linear relationship among piezoelectric strain coefficient, remanent polarization and the poling field.;P(VDF-HFP) copolymer is further investigated for its use in multiferroic ME composite, and various chemical modifications and processing methods are utilized to alter the crystalline structure. (Abstract shortened by UMI.).

【摘要机译】导电聚合物和机电聚合物是尖端电活性聚合物的两个重要分支。它们已对许多现代技术产生了重大影响,例如平板显示器,能量传输,能量转换,传感器和执行器。为了在微电子学,光电子学和热电学中使用导电聚合物,有必要对它们的热导率进行全面研究,因为热导率是基本的材料特性,这一特性尤其重要,有时甚至是决定器件性能的因素。对于机电聚合物,较大的压电效应将有助于提高其多铁复合材料的磁电(ME)耦合效率。本论文致力于表征导电聚合物的电导率和热导率,并开发新型的机电聚合物和应变介导的机电聚合物基多铁磁ME复合材料。导电聚合物为结合新型电学和​​热学性质的器件开辟了新的可能性。 ,但对电导率和热导率的长度尺度效应以及电和热传递行为的潜在机理的了解有限。本文提出了分析模型和实验技术来测量聚苯胺薄膜的面内热导率。对于使用光刻和反应性离子刻蚀在氧化硅/硅衬底上构图的掺杂樟脑磺酸的聚苯胺,测得厚度为20 nm的薄膜的热导率为0.0406 W / m·K,大大偏离了其体积(> 0.26) W / m·K)。在此尺度上,尺寸对导热系数的影响归因于明显的声子边界散射。当膜达到130nm厚时,热导率增加到0.166W / m·K,极大地受到声子-声子散射和声子边界散射的影响。当薄膜厚度大于130 nm时,热容量在聚苯胺的热传导中也起着重要作用。;扩展了相同的技术来测量掺杂有不同樟脑磺酸含量的55 nm厚聚苯胺薄膜的电导率和热导率。结果表明,掺杂水平(樟脑磺酸/聚苯胺比率)对电导率的影响比对热导率的影响更为明显,从而极大地影响了决定热电效率的比率。在60%的掺杂水平下,聚苯胺薄膜由于形成了大部分离域的极化子结构,因此具有最大的电导率和导热率。建议极化子是负责导电的电荷载体,而声子则在掺杂的聚苯胺薄膜的热传导中起着主导作用。;多铁性材料结合了不同寻常的弹性,磁性和电学性质,在许多领域具有广阔的应用前景,例如传感器,传感器和读/写存储设备。对于应变介导的多铁性ME复合材料,其ME效应是作为压电相和磁致伸缩相的产物而产生的。本文研究并提出了新型的多铁性复合材料。其中之一是基于链端交联的铁电聚偏二氟乙烯-共三氟乙烯(PVDF-TrFE)。在低直流偏置磁场下,该复合材料的非共振ME系数为17.7 V / cm Oe,共振为383 V / cm Oe,远高于目前文献中聚合物基ME复合材料的ME电压系数。本文还开发了基于聚偏二氟乙烯-共-六氟丙烯共聚物P(VDF-HFP)的ME复合材料。 P(VDF-HFP)中的结晶β相结构是通过单轴拉伸预熔融和淬火的薄膜而产生的。测量了在不同极化场下作为直流磁场函数的ME电压系数。发现复合材料的ME电压系数与极化场之间存在线性关系。此外,在P(VDF-HFP)中观察到电场诱导的相变,这由中间极化场的双磁滞D-E环向高极化场的单环演变而来。双磁滞回线是由于反铁电相在高电场下极化时会转变为铁电相。还发现在类铁电体和铁电体P(VDF-HFP)中,压电应变系数,剩余极化率和极化场之间存在线性关系。多铁ME复合材料,并使用各种化学修饰和加工方法来改变晶体结构。 (摘要由UMI缩短。)。

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