导热高分子材料研究进展

讨论了提高聚合物导热性能的途径－合成高导热系数的结构聚合物，用高导热无机填料对聚合物进行填充复合。综述了导热高分子材料的研究成果：聚合物导热的基本概念和影响其导热性能的因素及导热系数的预测理论；聚合物基导热复合材料的选材、复合技术及其应用。指出了导热高分子材料的研究方向－－纳米导热填料的研究和开发；聚合物树脂基体的物理化学改性；聚合物基体与导热填料复合新技术的研究和开发；复合材料导热模型的建立、导热机理（特别是聚合物基体与导热填料界面的结构与性能对材料导热性能的影响）及导热通路的形成等；探索高导热本体聚合物材料的制备方法和途径等。对导热高分子材料的研究和开发有重要意义。     

碳纤维随机填充橡胶复合材料导热性能的数值模拟

运用随机顺序添加算法RSA(Random sequential addition method),基于均匀化理论建立了碳纤维填充橡胶复合材料代表体积单元RVE(Representative volume element)模型,利用有限元方法数值模拟研究了碳纤维对橡胶复合材料导热性能的影响。结果表明:在相同的填充分数下,碳纤维根数对复合材料导热性能的影响较小;合理安排碳纤维空间分布及纤维取向能有效提高复合材料的导热性能;复合材料的导热性随着碳纤维填料含量及长径比的增加而增大;与理论模型相比,基于碳纤维填料随机分布模型所得模拟结果与实验值较接近,尤其在高填充分数时与实验值吻合较好,可以更好地预测纤维填料填充复合材料的导热性能,对制备具有高填充分数的高导热复合材料具有一定的指导意义。     

微纳米复合导热材料的制备及导热性能

采用超声处理方法将膨胀石墨剥离成微纳米石墨片,并以制备的微纳米石墨片为导热填料采用溶液共混法对聚偏氟乙烯(PVDF)进行改性,制备出微纳复合导热材料。通过扫描电子显微镜对其微观结构进行了表征,结果表明通过超声处理可以使膨胀石墨发生部分剥离得到微纳米石墨片。导热性能测试结果表明,复合材料的导热性能随着超声处理时间的增加而增加;当超声处理时间为150min时,复合导热材料的导热系数是膨胀石墨填充PVDF的1.8倍。     

填充颗粒导热性对复合材料导热性能的影响

基于ANSYS Workbench稳态热分析模块,利用均匀化方法,研究了填充颗粒导热性对填充型复合材料导热性能的影响。结果表明,依靠增大填充颗粒导热系数来提高复合材料整体的导热性能有一定局限性,填料导热系数与基体材料导热系数之比存在一个临界值。在相同体积分数下,随着比值的增大复合材料导热系数增加,当达到临界值后继续增大比值复合材料的导热系数基本不变。不同形状的填充颗粒有不同的临界值,圆柱形颗粒的临界值略大于正方体形和球形,而且对于同一种形状的填充颗粒,随着填充分数的增大临界值略有增加。     

基于Lattice-Boltzmann方法的填充型复合导热材料的导热性能数值分析

陶瓷被广泛用作催化燃烧的催化剂载体。为及时将反应热导出,避免催化剂烧结、失活,需提高陶瓷导热能力。针对通过填充高导热性的金属或无机填料的方法制成的陶瓷复合导热材料,引入二维九速度不可压格子多相Lattice-Boltzmann模型,对构造的5种规则填充形状(圆形、正八边形、正六边形、正四边形和正三角形)的陶瓷基复合材料进行了完整的二维导热过程的数值分析。结果表明,在相同的填料和填充体积分数下,三角形填充的复合材料有效导热系数最大,填充形状愈趋近圆形则有效导热系数越小。同时模拟了各填充形状下,填充材料与基体材料的导热系数之比kp/km对复合材料有效导热系数的影响。研究结果表明,孤立的导热填料对于复合材料导热系数的提高作用是有限的,当kp/km增大到一定程度,有效导热系数不再明显增加。     

介电陶瓷/导热硅橡胶复合材料的制备及介电性能研究

针对单一导热填料在高填充量下也无法同时提高硅橡胶介电、导热性能的问题,采用介电陶瓷钛酸锶(ST)、导热填料氮化硅(Si_3N_4)复合填充制备了Si_3N_4/ST/硅橡胶复合材料,研究了复合材料的介电和导热性能。采用LCR频谱分析仪和导热系数测试仪分别测试复合材料的介电常数和导热系数。结果表明:Si_3N_4与ST的共同填充提高了复合材料的介电性能和导热系数;Si_3N_4填充量为15%(体积分数,下同)时,Si_3N_4/硅橡胶复合材料的介电常数达到最大值5.4F/m;在Si_3N_4填充量保持不变、ST填充量为20%时,复合材料介电常数为纯硅橡胶介电常数的2.3倍,介电损耗保持在0.05以下,导热系数是纯硅橡胶的3倍。     

导热硅橡胶的制备及性能研究

与其它合成橡胶相比,硅橡胶具有优异的耐高低温、耐候、耐老化、电气绝缘、生理惰性等优点.当配合加入无机导热填料(如金属粉末、金属氧化物、氮化物等)后可制成导热硅橡胶.虽然导热硅橡胶的研究历史不长,但它已逐步得到了实际应用,并且随着现代科学技术和工业生产的发展,其应用领域越来越广,用量越来越大,对其性能的要求也越来越高.但是,目前对导热硅橡胶的研究重在应用方面,其理论研究滞后于应用研究,且理论研究仅仅为初步,并不深入.因此在设计开发高品质导热硅橡胶的同时,重点对导热硅橡胶进行了基础理论研究. 选择ZnO、Al2O3、SiC、AIN、BN 5种导热填料填充的导热硅橡胶作为研究对象,对导热硅橡胶的导热性能、力学性能、熟稳定性、各种影响因素及其作用机理等进行了研究;以导热硅橡胶的TGA数据为基础,研究了导热填料对硅橡胶热稳定性及其热降解动力学的影响,并对其热降解动力学参数进行了计算;通过溶液插层法制备VMQ/EG导热复合材料,将材料的结构、热稳定性、导热性等与传统熔融共混法制备VMQ/EG导热复合材料进行了对比,分析了影响材料导热性能的因素,探索了其导热机理;制备了具有导热性的硅橡胶/EPDM并用胶,并研究了导热填料对并用橡胶力学性能、导热性能的影响. (1)导热硅橡胶的性能研究.以甲基乙烯基硅橡胶作为基胶,以气相白炭黑为补强剂,考察了导热填料ZnO、Al2O3、SiC、AIN、BN对所填充的高温硫化导热硅橡胶性能的影响.研究发现,所得导热硅橡胶的各项性能与所用导热填料种类密切相关,SiC>AIN>Al2O3>ZnO>BN.对制备的导热硅橡胶的导热系数进行理论拟合,结果发现材料导热系数与Agari方程拟合较好.多种粒径导热填料配合使用能够显著提高橡胶导热性能,例如选用不同粒径的Al2O3导热填料制备的导热硅橡胶,当m(Φ27nm):m(Φ2μm)=3:1、m(Φ50μm):m(Φ50μm)=1:3或3:1时,所得硅橡胶的导热系数提高较大.导热填料经过表面处理后制备的硅橡胶导热系数有明显提高,其中用A-172处理Al2O3效果最好,比未处理时(0.546 W/(m·K))提高了12.7%.硅橡胶交联密度增加,导热网络变得更加致密,硅橡胶导热系数也增加,但当连续致密的导热网络形成以后,交联状态对硅橡胶导热系数的影响不再明显.降低硫化温度能够显著提高硅橡胶的导热系数,当硫化温度从160℃降到120℃时,所得硅橡胶的导热系数增加了5.5%;当硫化温度从120℃降到80℃时,导热系数增加24.9%.硅橡胶/Al2O3、硅橡胶/ZnO的导热系数随温度的升高而降低,随导热填料用量增加,硅橡胶的导热系数降低的程度增大;导热硅橡胶材料中存在明显的PTC(正温度系数)现象. (2)导热硅橡胶热降解动力学研究.应用TGA数据,采用改进的Freeman-Carroll方法对填充导热填料Al2O3和ZnO的导热硅橡胶的热降解动力学参数进行了计算,发现导热硅橡胶的起始热降解反应温度较高,其相应的反应活化能也大于空白硅橡胶.导热硅橡胶的热降解反应以零级反应为主,反应活化能是温度的函数,而且对温度的敏感性随温度的升高而变弱. (3)溶液插层法制备硅橡胶/膨胀石墨(VMQ/EG)导热复合材料.用X射线衍射对制备的VMQ/EG复合物进行了结构表征.对比溶液插层法和熔融共混法制备的VMQ/EG复合材料发现,EG用量小时,溶液插层法制备的VMQ/EG复合材料导热系数较高,并且能够显著改善硅橡胶的热稳定性能.这是因为溶液插层法制备的VMQ/EG复合材料中EG在经过插层、混炼、模压成型等工序后不但保留了原始结构,而且变得更紧密;而熔融共混法制备的VMQ/EG复合材料中EG的网络结构被彻底破坏.插层法制备的VMQ/EG复合材料虽然能够显著提高硅橡胶的导热性,但EG用量受到限制,硅橡胶导热性能的进一步提高非常困难.研究发现,当在VMQ/EG体系中继续加入第三组分(如SiC、AlN、BN、Al2O3、ZnO、碳纤维(CF)等)时可以进一步提高VMQ/EG材料的导热系数. (4)硅橡胶/三元乙丙橡胶(EPDM)导热并用胶研究.系统研究了固定硅橡胶与EPDM配比的条件下,增容剂Si69以及硫化荆DCP用量对并用导热硅橡胶力学性能的影响,以及导热填料及配合方法等对并用橡胶的力学性能、导热性能的影响.硅橡胶/EPDM并用导热硅橡胶与纯导热硅橡胶相比,其力学性能可得到显著提高.并用橡胶的热稳定性介于纯硅橡胶和EPDM之间.     

填充型导热聚合物基复合材料的研究进展

阐述了填充型导热聚合物基复合材料的导热机理、导热模型和测试方法等,重点介绍了聚合物基导热复合材料的研究进展及基体、填料、表面改性对复合材料导热性能的影响,最后展望了聚合物基导热复合材料的发展趋势。     

聚合物复合材料导热性能的研究

论述了填充聚合物复合材料的导热性及其变化规律；总结了复合材料导热的理论模型和导热系数预测方程，对比研究了各种导热模型的区别与联系；分析了影响复合材料导热特性的因素。     

碳纳米管/橡胶复合材料导热性能研究进展

导热橡胶在航空、航天、电子、电器领域有着广泛的应用前景。把碳纳米管填充到橡胶中,渴望获得具有优良导热性能的橡胶复合材料已成为材料领域研究的热点。本文综述了填充型导热橡胶的实验研究现状、导热橡胶的导热机理、导热模型;重点论述了碳纳米管的结构与改性、碳纳米管填充橡胶的导热性能的实验研究及理论研究进展;最后指出碳纳米管的独特结构和优异性能使其作为橡胶复合材料导热增强组分在理论上具有明显优势,但其复合材料的热物性研究仍存在一些问题有待解决;如何降低界面热阻、增加碳纳米管取向等将是提高碳纳米管/橡胶复合材料导热性能的重要解决途径。     

Thermally conductive polyamide 6/carbon filler composites based on a hybrid filler system

Abstract

We explored the use of a hybrid filler consisting of graphite nanoplatelets (GNPs) and single walled carbon nanotubes (SWCNTs) in a polyamide 6 (PA 6) matrix. The composites containing PA 6, powdered GNP, and SWCNT were melt-processed and the effect of filler content in the single filler and hybrid filler systems on the thermal conductivity of the composites was examined. The thermal diffusivities of the composites were measured by the standard laser flash method. Composites containing the hybrid filler system showed enhanced thermal conductivity with values as high as 8.8 W (m · K)^?1, which is a 35-fold increase compared to the thermal conductivity of pure PA 6. Thermographic images of heat conduction and heat release behaviors were consistent with the thermal conductivity results, and showed rapid temperature jumps and drops, respectively, for the composites. A composite model based on the Lewis–Nielsen theory was developed to treat GNP and SWCNT as two separate types of fillers. Two approaches, the additive and multiplicative approaches, give rather good quantitative agreement between the predicted values of thermal conductivity and those measured experimentally.     

Thermally conductive polyamide 6/carbon filler composites based on a hybrid filler system

We explored the use of a hybrid filler consisting of graphite nanoplatelets (GNPs) and single walled carbon nanotubes (SWCNTs) in a polyamide 6 (PA 6) matrix. The composites containing PA 6, powdered GNP, and SWCNT were melt-processed and the effect of filler content in the single filler and hybrid filler systems on the thermal conductivity of the composites was examined. The thermal diffusivities of the composites were measured by the standard laser flash method. Composites containing the hybrid filler system showed enhanced thermal conductivity with values as high as 8.8 W (m · K)⁻¹, which is a 35-fold increase compared to the thermal conductivity of pure PA 6. Thermographic images of heat conduction and heat release behaviors were consistent with the thermal conductivity results, and showed rapid temperature jumps and drops, respectively, for the composites. A composite model based on the Lewis–Nielsen theory was developed to treat GNP and SWCNT as two separate types of fillers. Two approaches, the additive and multiplicative approaches, give rather good quantitative agreement between the predicted values of thermal conductivity and those measured experimentally.     

Thermal conductivity of ceramic particle filled polymer composites and theoretical predictions

Models and theories for predicting the thermal conductivity of polymer composites were discussed. Effective Medium Theory (EMT), Agari model and Nielsen model respectively are introduced and are applied as predictions for the thermal conductivity of ceramic particle filled polymer composites. Thermal conductivity of experimentally prepared Si₃N₄/epoxy composite and some data cited from the literature are discussed using the above theories. Feasibility of the three methods as a prediction in the whole volume fraction region of the filler from 0 to 1 was evaluated for a comparison. As a conclusion: both EMT and Nielsen model can give a well prediction for the thermal conductivity at a low volume fraction of the filler; Agari model give a better prediction in the whole range, but with larger error percentage.     

高导热低填量聚合物基复合材料研究进展

高导热低填量聚合物基复合材料在电子封装和大功率电子设备等领域有着巨大需求。通常高导热聚合物是通过在高分子基体中均匀分散高含量的导热填料来实现的,然而较高填料含量会极大地恶化复合材料力学性能和提升材料经济成本,因此高填量复合材料很难满足当前工业应用上的需求。综述了近年来高导热低填量聚合物基复合材料制备研究进展,简要介绍了导热机制和影响低填量聚合物基复合材料导热性能的主要因素,按照不同填料类型介绍了一些热导率高于1.0 W/（m·K）且填充量低于10vol%的高导热低填量聚合物基复合材料的制备方法和研究进展,展望了高导热低填量聚合物基复合材料的发展方向。     

石墨烯纳米片/(酚酞聚芳醚酮-环氧树脂)双逾渗导热复合材料的制备和性能

为在较低的导热填料含量下提高环氧树脂(EP)的热导率,通过溶液法制备了石墨烯纳米片/(酚酞聚芳醚酮-EP) (GNP/(PEK-C-EP))复合材料。基于接触角测量计算并预测了GNP的选择性分布,并通过SEM和激光闪光法研究了GNP和PEK-C含量对GNP/(PEK-C-EP)复合材料的微观结构和热导率的影响。结果表明,当PEK-C的含量为20wt%时,GNP选择性分布在PEK-C中,形成了双逾渗结构的GNP/(PEK-C-EP)复合材料,从而构建了连续导热通道。当GNP含量为1wt%时,GNP/EP复合材料导热率最高达0.375 W(m·K)?1。当GNP含量为0.5wt%时,GNP/(PEK-C-EP)复合材料导热率最高达0.371 W(m·K)?1,较GNP含量为0.5wt%的GNP/EP复合材料热导率高48%,与GNP含量为1wt%的GNP/EP复合材料的热导率基本相同。表明GNP/(PEK-C-EP)复合材料的填料量减少了50%,利用双逾渗效应可以有效减少导热填料用量。此外,比较了纯EP和GNP/(PEK-C-EP)复合材料的玻璃化转变温度、热稳定性和热膨胀系数,结果表明,GNP/(PEK-C-EP)复合材料的热性能优于纯EP。      

On the Lewis–Nielsen model for thermal/electrical conductivity of composites

Several models have been proposed in the literature to describe the thermal and electrical conductivities of particulate composites. Among the proposed models, the Lewis–Nielsen model appears quite attractive as it is simple to use and it predicts the correct behavior when filler concentration () approaches the maximum packing concentration (_m). In this paper, the Lewis–Nielsen model is evaluated in light of a vast amount of experimental data available on thermal and electrical conductivities of particulate composites. The Lewis–Nielsen model is found to describe the experimental data for both thermal and electrical conductivities reasonably well.     

两种典型星用聚合物介质抗内带电改性防护技术研究

空间高能电子辐射易造成星用聚合物介质内带电水平过高,是卫星运行可靠性的潜在威胁因素。对航天器介质材料进行非线性电导改性是提高航天器介质材料自释电荷能力,进而降低内带电水平的有效方法。实验选用半导电无机添加剂对典型空间聚合物材料聚四氟乙烯、聚酰亚胺进行改性工艺和电导特性研究,测量了常态体电导率与添加剂含量关系,不同含量添加剂下复合材料体电导率随温度与电场的变化规律以及复合材料的导热性能参数。实验表明,添加剂含量会显著影响复合材料的体电导特性及导热特性,特别是复合材料的非线性电导特性阈值电场降低最为明显。这种既能保持高绝缘性能又具有良好非线性电导特性的新型复合介质材料,有希望成为从根本上解决星用聚合物介质深层带电问题的有效措施。     

A Study on Microsized Titanium Oxide-Filled Epoxy with Enhanced Heat Conductivity for Microelectronic Applications

This article presents a study on the thermal conductivity characterization of microsized TiO₂-filled epoxy composites. Titanium oxide (TiO₂) particles of about 100 µm mean size are embedded in epoxy resin to develop composites by hand layup technique. Effective thermal conductivity values of these samples are measured using Unitherm Model 2022 in accordance with ASTM-E 1530 standards. The measured values are then compared with those obtained from a mathematical correlation deduced basing upon a one-dimensional heat conduction model developed by the authors previously. This study reveals that there is a significant improvement in thermal conductivity of the composites with increase in TiO₂ content. With addition of 25 vol% of TiO_2, the thermal conductivity of epoxy composite improves by about 223%. On comparing the measured conductivity values with those obtained from the theoretical model, it has been observed that the measured values are in very good agreement with the theoretical values for low filler concentrations (0–17.5 vol%). It is further seen that TiO₂ particles show percolation behavior in epoxy matrix at about 17.5 vol% of filler content at which a sudden jump in the conductivity value is noticed.     

Thermal conductivity of metal powder-polymer feedstock for powder injection moulding

Thermal conductivity of a powder injection moulding feedstock (mixture of metal powders and polymers) in solid and molten states has been measured by using the laser flash method. The filler material was 316L stainless steel powder and its content in the mixture amounted 60% by volume. An attempt has been made to employ two most promising existing mathematical models (theoretical Maxwell- and semi-theoretical Lewis & Nielsen model) to calculate the thermal conductivity of the mixture. Comparison of the experimental and calculated results has revealed that the Lewis & Nielsen model predicts better than Maxwell model the thermal conductivity of the feedstock. As the difference between the calculated (Maxwell model) and the measured results amounts to 15–85%, it is suggested that it can only be used for preliminary assessment of the thermal conductivity of so highly filled composite material. If accurate thermal conductivity data are required (as in case of numerical simulation of the powder injection moulding process), measurement of this property has to be performed if meaningful simulation results are to be expected.