六方氮化硼/聚合物导热复合材料研究进展

随着电子技术快速的发展,聚合物材料自身较低的热导率已不能满足现代电子器件的散热需求,因此提高聚合物热导率,实现高效率的传热具有重要意义。六方氮化硼(h-BN)具有良好的高电击穿强度,导热性能、介电性能、低吸湿率、高温耐氧化等诸多特性,是制备低介电常数、低介电损耗和高导热聚合物的理想填料。本文分别从目前制备BNNSs的主要方法及提高BN复合材料热导率的不同思路两个方面,综述了以六方氮化硼(h-BN)为填料的导热聚合物复合材料的研究现状。     

Ag负载KTa1-xNbxO3-BaTiO3颗粒掺杂P(VDF-TrFE-CTFE)复合材料的制备及介电性能

通过光照还原法制备了银颗粒负载的铌钽酸钾-钛酸钡复合粉体（Ag/KTN-BT）,并将其与聚偏氟乙烯-三氟乙烯-三氟氯乙烯（P（VDF-TrFE-CTFE））聚合物复合,获得Ag/KTN-BT聚合物基复合材料。研究发现,Ag/KTN-BT填料颗粒在聚合物基体中分散均匀,复合材料结构致密,无明显气孔和裂纹,且具有较好的柔韧性。银纳米颗粒的负载,一方面在复合材料中引入了额外的界面,导致界面极化作用增强,明显提高复合材料的介电常数;另一方面银纳米颗粒的量子尺寸效应和库伦阻塞效应使得复合材料保持较低的介电损耗。当填充体积分数为20%的Ag/KTN-BT颗粒时,聚合物基复合材料的介电常数大幅提升,从聚合物的37提升到125（100 Hz）,介电损耗仅为0.12。与KTN-BT基复合材料对比,Ag/KTN-BT基复合材料也显示出较好的介电性能。     

纳米TiO_2/硅橡胶复合材料的制备及研究

介电弹性体是一种通过在其两端施加电压就能够获得变形的材料。硅橡胶类介电弹性体因变形响应速度快、可自由制备、温度适用范围广等优点而备受关注,但是因介电常数较低、激发电场强度较高、电致变形较小等缺点制约了其发展。针对这些问题,本文以液体硅橡胶为基体,以纳米TiO_2为填料,通过溶液混合法制备了纳米TiO_2/硅橡胶复合材料,并对其介电性能、电致变形性能进行测试。结果表明,通过在聚合物基体中添加纳米TiO_2,提高了其介电常数,降低了介电损耗,能够获得较大的电致变形。     

聚合物纳米复合电介质

聚合物纳米复合材料能够发挥纳米材料在电、磁、光等方面的优越性,也具有聚合物的易成型等方面的优点,正成为电介质领域研究的热点.本文综述了聚合物纳米复合材料在介电性能方面的研究概况,主要涉及了电导、介电强度与空间电荷、介电常数、介电损耗以及局部放电等方面的研究.最后展望了今后的研究方向.     

巨介电CCTO及CCTO/聚合物研究

具有类钙钛矿结构的钛酸铜钙CaCu3Ti4O12(CCTO)介电陶瓷材料以其巨介电特性、介电常数的温度和频率稳定性及非线性等特性在材料研究领域和实际应用中受到广泛关注。本文比较了CCTO各种巨介电理论和模型,详述了目前能够较合理地解释CCTO巨介电特性的内部阻挡层电容模型(IBLC)。综述了制备方法、制备条件及改性方法对CCTO介电性能的影响。离子掺杂是降低CCTO介电损耗常用的方法之一,掺杂效果受掺杂离子半径、离子价态等多种因素的影响。将陶瓷粉体与聚合物进行复合形成0-3型复合材料是目前制备综合性能良好的介电材料的有效方法,对CCTO/聚合物复合材料的研究进展进行了评述。最后,展望了CCTO陶瓷材料的发展前景。     

高介电常数树脂基复合材料的研究进展

高介电常数(high-k)树脂基复合材料(RMCs)以其良好的加工性能、突出的机械性能及优异的介电性能受到人们的广泛关注和重视,显示出巨大的应用潜力,因而成为近年来功能材料领域的研究热点。如何实现更高介电常数、更低介电损耗和更优异的力学性能成为该领域的研究重点。本文根据近年来high-k RMCs的研究现状,重点介绍了本课题组在该方向的研究进展,以期为综合性能优异的high-k RMCs的发展提供一些思路和方法。     

CP@hBT-CNT/PDMS三相介电复合材料的制备与性能

基于卡波姆（CP）和羟基化钛酸钡（hBT）之间的相互作用,通过CP对hBT的包覆制备了“核-壳”结构CP功能化改性的hBT杂化粒子（CP@hBT）。以CP@hBT为陶瓷填料,氨基化碳纳米管（CNT）为导电填料,聚二甲基硅氧烷（PDMS）为基体,利用溶液共混法制备CP@hBTCNT/PDMS介电复合材料。系统研究了CP功能化改性对CP@hBT-CNT/PDMS微观形貌和介电性能的影响。结果表明,CP对hBT功能化改性后可以有效减少CP@hBT杂化粒子的沉降和团聚问题,增强了其在PDMS基体中的分散性。在1 000 Hz条件下,当w(CNT)=0.75%时,CP@hBT-CNT/PDMS复合材料的介电常数可以达到138,同时介电损耗仍较低。     

颗粒填充聚合物高介电复合材料

颗粒填充聚合物高介电复合材料兼具聚合物材料的易加工、低损耗、耐击穿性能和陶瓷材料的高介电等性能,还可使金属材料具备介电性能,可以广泛应用于电气、电子行业。本文综述了非均匀体系介电理论研究的历史背景,以及陶瓷、金属颗粒填充聚合物高介电复合材料的组成、制备及介电性能的影响因素,并着重讨论了界面相在复合材料研究中的重要性,最后展望了发展方向。     

Ba0.6Sr0.4TiO3/聚偏氟乙烯-聚甲基丙烯酸甲酯复合材料的制备及其介电性能

采用流延热压工艺制备Ba_0.6Sr_0.4TiO₃(BST)/聚偏氟乙烯(PVDF)?聚甲基丙烯酸甲酯(PMMA)复合薄膜,研究了PMMA含量对复合材料微观组织结构和介电性能的影响规律。结果表明,BST相能够均匀分散在聚合物基体中,归因于PMMA与PVDF良好的相容性,2种聚合物之间的界面不分明;随着PMMA含量的增加,复合材料的介电常数先降低后升高,耐击穿强度和介电可调性先增加后减少。PMMA含量(体积分数)为15%的BST/PVDF?PMMA₁₅复合材料的综合性能最佳:介电常数为23.2,介电损耗为0.07,耐击穿强度为1412 kV·cm^-1,在550 kV·cm^-1偏压场下,介电可调性为26.2%。     

碳纳米管-聚乙烯复合材料的介电性能

采用熔融共混及模压的方法制备了碳纳米管(CNT)-高密度聚乙烯(HDPE)复合材料,并用介电谱仪研究了逾渗值附近的导电填料对复合材料体系在不同温度、频率条件下的介电常数、介电损耗、交流电阻率的变化规律。结果表明:复合材料的介电常数、介电损耗均随CNT质量分数增加而逐渐增大;在频率为103~106 Hz,温度为40~130℃时,HDPE基体的介电常数随频率和温度的变化较小,而添加CNT填料的复合材料的介电常数随频率和温度的增加而略微降低。当w(CNT)0.5%时,复合材料的交流电阻率表现出对频率的强烈依赖性;而当w(CNT)0.5%时,在低频处表现出直流特性,在高频处显示出交流电阻率的降低。     

纤维素基介电材料

作为电荷的高效存储设备,介电电容器受到学术界和产业界越来越多的关注,其中介电材料是介电电容器的核心。长久以来,双向拉伸聚丙烯和聚对苯二甲酸乙二醇酯等石油基聚合物作为介电材料广泛应用于商用电容器设备。然而,随着服役环境的变化(如工作温度升高等),聚合物材料的介电常数与充放电效率下降,同时介电损耗与电流漏导增加,导致储能密度大幅降低,亟待开发具有高储能密度的新型可持续聚合物介电材料。纤维素是地球上储量最丰富的天然聚合物,具有可持续、价格低廉、可生物降解等特点,是理想的候选生物基材料。近年来,通过将纤维素纳米纤维、氰乙基纤维素、再生纤维素及醋酸纤维素分别与不同填料进行复合,显著提高了介电常数、击穿场强与充放电效率,获得了一系列具有高储能密度的生物基介电材料。本文总结了上述纤维素基介电材料的研究进展,并对该领域面临的挑战与发展前景进行了探讨与展望。     

Dielectric studies of As-Se glasses

Dielectric constants and loss tangents of As-Se glasses have been measured between 300 K and the respective glass transition temperatures and between 1 kHz and 20 kHz. The variation of dielectric constants has been interpreted in terms of both heteropolarity of bonds and average bond energies employing a chemically ordered network model. Various contributions to total molar polarizations have been estimated. Rapid rise of loss tangent in the vicinity of glass transitions has been interpreted in terms of rapid increase; of d.c. conductivity. Communication No. 108 from Solid State and Structural Chemistry Unit.     

Dielectric studies on some mesogenic,non-mesogenic and organic molecules

Two important molecular parameters, namely, the dielectric relaxation time τ and electric dipole moment are highly useful in having insight into the molecular structure, size, shape, apart from the inter- and intra-molecular forces, etc. With these in view dielectric measurements in benzene at room temperature on the pure samples of o-ethyl phenol, 2-n-butylphenol, 4-n-butylphenol, 2,6-dimethoxyphenol and 3,4-difluorophenol were carried out at a frequency of 9.98 GHz by employing concentration variation method. Similar measurements, on a single weight fraction of each of them at 9.98 GHz and also at 8.74 GHz are carried out. Measurements on a single weight fraction in benzene of each of the liquid crystal samples, namely, EPCP.car (Butyl-p-(p-ethoxy phenoxy corbonyl)-phenyl carbonate), PPPB (p-pentylphenyl-p-propyl benzonate), EPAP.Hp (p-(p-ethoxyphenyl azo) phenyl heptenate) and EPAP. Und (p-(p-ethoxyphenyl azo) phenyl undecylenate were also carried out at the said two frequencies. Using the obtained values of ε′, ε′′ relaxation time and dipole moment were determined using different methods. The obtained results are compared with earlier results wherever available.     

Advances in the Study of Gas Hydrates by Dielectric Spectroscopy

The influence of kinetic hydrate inhibitors on the process of natural gas hydrate nucleation was studied using the method of dielectric spectroscopy. The processes of gas hydrate formation and decomposition were monitored using the temperature dependence of the real component of the dielectric constant ε′(T). Analysis of the relaxation times τ and activation energy ΔE of the dielectric relaxation process revealed the inhibitor was involved in hydrogen bonding and the disruption of the local structures of water molecules.     

Dielectric relaxation studies of aromatic polyamides

Dielectric relaxation spectroscopy (DRS) is presented for a family of four aromatic polyamides trying to relate the structure of the lateral groups to the molecular mobility. A prominent sub-T_g absorption is always seen followed in some cases by remanent dielectric activity at room temperature and a subsequent increase of the loss permittivity. The low temperature relaxation is analyzed in terms of a Fuoss–Kirkwood equation to obtain the broadness and the strength of these relaxations as well as the activation energy (ranging from 10 to 11 Kcal/mol). The low frequency conductive peak shows in each case a half-width higher (1.30) than those corresponding to a single relaxation time peak (1.144). These values of the half-width are an indication of the complex character of these phenomena. A final discussion of the rotational barriers of the lateral chains rules out that such motions are the only molecular origin for the gamma relaxation. Instead, some kind of motion involving the main chain and where the interchain interactions play a significant role should be considered as responsible for that relaxation. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 919–927, 1997     

Dielectric relaxation measurements on aerosol-OT/water/cyclohexane-solutions at low water content

The complex relative dieletric permittivity of aerosol-OT(AOT)/water/cyclohexane solutions has been measured within the frequency range 5 kHz-10 GHz. The investigated solutions were of oil-rich type with varying AOT- and water content. A marked dielectric relaxation has been found. The dielectric increment as well as the conductivity steeply increase with the water content, while the relaxation time decreases. Theoretical models of heterogeneous dielectrics consisting of polar, highly conductive inclusions in a nonpolar solvent with low conductivity have been applied to the results, allowing conclusions with regard to the inclusions, shape and conductivity.     

马来二腈基二硫烯镍(Ⅱ)配合物展现了介电反常和弛豫

合成并用X-射线单晶衍射表征了一个离子对化合物1,7-bis(1-methylimidazolium)heptane bis(maleonitriodithiolato)nickelate(1)的结构。沿着晶体学c轴方向,化合物1中的阴、阳离子分别排列形成波浪形的链。变温介电性质研究表明,化合物1在90℃左右展现了介电态转变。我们将此转变归于化合物1中平衡阳离子的有序到无序转变。在低频区,化合物1出现了明显的介电弛豫过程,这与阳离子偶极运动有关。此外,DSC研究表明,在第二个升温过程中,化合物1在66℃和130℃左右出现两步冷结晶。此种冷结晶现象在小分子化合物中很罕见,这与化合物1的较大粘度以及测试过程中的较快降温速率有关。     

马来二腈基二硫烯镍（Ⅱ）配合物展现了介电反常和弛豫

合成并用X-射线单晶衍射表征了一个离子对化合物1,7-bis（1-methylimidazolium）heptane bis（maleonitriodithiolato）nickelate（1）的结构。沿着晶体学c轴方向,化合物1中的阴、阳离子分别排列形成波浪形的链。变温介电性质研究表明,化合物1在90℃左右展现了介电态转变。我们将此转变归于化合物1中平衡阳离子的有序到无序转变。在低频区,化合物1出现了明显的介电弛豫过程,这与阳离子偶极运动有关。此外,DSC研究表明,在第二个升温过程中,化合物1在66℃和130℃左右出现两步冷结晶。此种冷结晶现象在小分子化合物中很罕见,这与化合物1的较大粘度以及测试过程中的较快降温速率有关。