氮化硼纳米片制备及其改性复合材料导热性能研究进展

氮化硼纳米片(BNNSs)是一种二维片状纳米材料,具有较高的导热性和热稳定性.将其作为填料加入聚合物中,可显著提高复合材料的导热性能.基于近年来对BNNSs改性复合材料的导热性能的研究进展,总结了BNNSs的制备和改性方法,介绍了该体系复合材料的导热机理,分析了影响复合材料导热性能的因素,最后对该体系复合材料的导热性能研究进行了展望.     

复合材料导热性能的研究综述

简述了聚合物基复合材料的导热性能以及导热填料工作反应机制,综述了一些直接影响复合材料导热性能的主要因素以及填料改性处理的方法。同时也展望了一些关于导热复合材料未来的相关技术应用研究的发展和方向。     

表面改性处理对EP/BN复合材料导热及力学性能的影响

采用硅烷偶联剂KH-550对氮化硼(BN)进行表面改性,并对改性的BN进行了X射线光电子能谱分析(XPS),考察了BN表面改性对EP/BN绝缘导热复合材料导热性能和力学性能的影响。结果表明:添加适量的偶联剂能够提高EP/BN复合材料的热导率,但是随着添加偶联剂用量的增加,复合材料的导热性能逐渐下降;另外,由表面改性BN制备的复合材料,其拉伸强度明显低于其他EP/BN复合材料。     

氧化铝的表面改性及其对BR导热性能的影响

采用不同品种偶联剂对氧化铝进行表面湿法改性,制备改性氧化铝/BR复合材料,研究复合材料的物理性能和导热性能.结果表明:硅烷偶联剂KH-550湿法改性氧化铝/BR复合材料的物理性能最佳,硬脂酸湿法改性氧化铝/BR复合材料的导热性能最佳;随着硬脂酸于法改性氧化铝用量的增大,复合材料的硬度、拉断伸长率及导热系数明显增大;在硬脂酸干法改性氧化铝/BR复合材料中加入炭黑N330,复合材料的物理性能提高,导热性能基本不变.     

PEK-CN/SiC复合材料的制备及热学性能

以酚酞聚芳醚腈酮(PEK-CN)为基体、碳化硅(SiC)为导热填料，用硅烷偶联剂(KH550,KH560及KH570)对SiC进行表面改性，通过静电纺丝技术和高温模压法制备了PEK-CN/SiC复合材料，研究了SiC含量和不同偶联剂改性SiC对PEK-CN/SiC薄膜的微观形貌、PEK-CN/SiC复合材料的导热性能和热稳定性的影响。结果表明：偶联剂改性SiC后以及随着SiC含量的增加，PEK-CN/SiC复合材料的导热性能与热稳定性均有所改善。当经KH560表面改性的SiC质量分数为25%时，复合材料的导热系数最大，达到了0.586 W/(m·K),比PEK-CN导热系数提高了133.5%,玻璃化转变温度、失重5%及30%时的温度较PEK-CN分别提升了3.79,0.37,225.76℃。     

导热型环氧复合材料的研究进展

介绍了导热型环氧复合材料导热性能和导热机理。并综述各类导热环氧复合材料的研究进展,在此基础上讨论提高复合材料导热性能的途径。     

改性石墨对天然橡胶复合材料导热性能的影响

研究表面活性剂或不同偶联剂对石墨改性效果以及石墨用量对天然橡胶(NR)复合材料物理性能、导热性能及微观结构的影响。结果表明:偶联剂Si69对石墨的改性效果最好,石墨呈现亲油性;与未改性石墨填充NR复合材料相比,偶联剂Si69改性石墨填充NR复合材料中石墨与NR间的界面相容性得到改善,物理性能和导热性能提高;随着偶联剂Si69改性石墨用量的增大,复合材料导热性能提高,物理性能先提高后下降。当改性石墨用量为30份时,复合材料的综合性能较好。     

不同粒径氮化硼填充环氧树脂/玻璃纤维绝缘导热复合材料的研究

以聚砜改性环氧树脂为基体,通过高温模压制备了环氧树脂/玻璃纤维/氮化硼复合材料,研究了不同粒径及不同氮化硼导热粒子用量对复合材料导热性能、力学性能和电性能的影响。结果表明,大粒径粒子有利于复合材料力学性能的提高,小粒径有利于导热性能的提高;随着氮化硼用量的增加,复合材料的导热性能升高,力学性能呈现先增后降趋势,当氮化硼用量为10%(质量分数,下同)时,复合材料的冲击强度和弯曲强度均达到最佳,当氮化硼用量为20%时,复合材料仍保持较好的电性能。     

不同粒径氮化硼填充环氧树脂/玻璃纤维

以聚砜改性环氧树脂为基体,通过高温模压制备了环氧树脂/玻璃纤维/氮化硼复合材料,研究了不同粒径及不同氮化硼导热粒子用量对复合材料导热性能、力学性能和电性能的影响。结果表明,大粒径粒子有利于复合材料力学性能的提高,小粒径有利于导热性能的提高;随着氮化硼用量的增加,复合材料的导热性能升高,力学性能呈现先增后降趋势,当氮化硼用量为10 %（质量分数,下同）时,复合材料的冲击强度和弯曲强度均达到最佳,当氮化硼用量为20 %时,复合材料仍保持较好的电性能。     

碳纳米管/聚乙烯导热系数分子动力学模拟

采用平衡分子动力学模拟方法研究了碳纳米管(CNT)/聚乙烯(PE)复合材料的导热系数。结果表明,使用长度为0.738nm的单壁CNT填充,CNT/PE复合材料的导热系数可达7.2 W/(m·K),增加CNT的填充量,复合材料的导热系数值随之增大;由于官能团改性造成的CNT缺陷阻碍了CNT自身热传导过程中声子的传播,官能团改性CNT填充虽然也能很大程度地提高了复合材料的导热系数,但其效果却不及CNT,模拟结果表明,CNT可成为提高PE导热性能的优良添加剂。     

The effect of boron nitride nanosheets on the mechanical and thermal properties of aluminum nitride ceramics

The boron nitride nanosheets (BNNSs)/aluminum nitride (AlN) composites were prepared by hot press sintering at 1600°C. The microstructure, mechanical properties, and thermal conductivity of the samples were measured, and the effect of adding BNNSs to AlN ceramics on the properties was studied. It is found that the addition of BNNSs can effectively improve the mechanical properties of AlN. When the additional amount is 1 wt%, the bending strength of the sample reaches the maximum value of 456.6 MPa, which is 23.1% higher than that of the AlN sample without BNNSs. The fracture toughness of the sample is 4.47 MPa m^1/2, a 68.7% improvement over the sample without BNNSs. The composites obtained in the experiment have brilliant mechanical properties.     

Fabrication of High Thermally Conductive and Electrical Insulating Composites by Boron Nitride-Nanosheet-Coated PEEK Fiber

The development of polyether ether ketone (PEEK)-based thermally conductive insulating composites is required in miniaturized electronic devices with a high power density where heat needs to be evacuated. However, the low thermal conductivity (TC) remains a great challenge, significantly restricting the large-scale applications of PEEK. Here, a novel class of boron nitride nanosheets (BNNSs)/PEEK composites with excellent heat dissipation properties through BNNS-coated PEEK fiber is developed, through simple hot-press sintering. A direct comparison of experimental measurements between the BNNSs/PEEK fiber composites and the BNNSs/PEEK powder composites indicates that the TC is greatly improved in the presence of the well-orientated structure of BNNSs. In addition, the composite with high loading of BNNSs exhibits a combination of high tensile strength and significant electrical insulation (volume electrical resistivity beyond 10⁹ Ω cm). The experimental data demonstrate that it has broad and bright prospects for application in a range of emerging electronic devices, which also provide great potential for enhancing the thermal management application of PEEK-based composites.     

Green and efficient production of boron nitride nanosheets via oxygen doping-facilitated liquid exfoliation

As the structural analogue of graphene, boron nitride nanosheets (BNNSs) are anticipated to have a wide range of potential applications. BNNSs exhibit good mechanical properties, outstanding thermal conductivity, oxidation and chemical stability and are excellent electrical insulators. While BNNSs have gained recognition as one of the most versatile 2D materials in recent years, their application in research and industry is still hampered by the lack of methods to produce BNNSs in large quantity and a cost-effective way. In this study, we report highly efficient h-BN exfoliation via the oxygen doping-facilitated liquid exfoliation. Oxygen atoms are introduced into the hexagonal boron nitride (h-BN) structure via a facile thermal treatment. The relationship of thermal treatment, structural changes and h-BN exfoliation are studied to elucidate the key factor for advancing the BNNS production. The optimum concentration of hydroxyl groups and weakening of interlayer interactions have synergistically facilitated the delamination of h-BN in water under mild exfoliation conditions, resulting in up to 1255% yield increment and without noticeable new defects in the BNNS structure as compared with the untreated control. An efficient and environmentally friendly exfoliation process of h-BN is a crucial starting point towards the cost-effective and mass production of BNNSs which is needed for the currently identified and myriad future applications of BNNSs.     

Large‐scale synthesis of hexagonal boron nitride nanosheets and their improvement in thermal properties of epoxy composites

In this study, we report a novel method to synthesize hexagonal boron nitride nanosheets (BNNSs) using a ball‐milled mixture of ammonium fluoroborate and sodium borohydride as precursor, under an ammonia atmosphere. The detailed morphological and structural investigations of the BNNSs are carried out by means of scanning electron microscopy, transmission electron microscopy (TEM), and high‐resolution TEM, and detailed formation process of the BNNSs is proposed. We further utilize the BNNSs and acid‐treated BNNSs (ATBNNSs) as nanofillers to fabricate a series of epoxy nanocomposites and study their varied thermal properties. The results indicate that the surface treatment and different fractions of BNNSs can discriminatively influence the thermal properties of epoxy nanocomposites. We also estimate the thermal conductivity channel thresholds with different ATBNNSs and BNNSs fractions. Through this work, an understanding of the interface treatment and filler fraction effects on thermal properties of epoxy nanocomposites is obtained. POLYM. COMPOS., 35:1707–1715, 2014. © 2013 Society of Plastics Engineers     

Novel Poly(m‐phenyleneisophthalamide) Dielectric Composites with Enhanced Thermal Conductivity and Breakdown Strength Utilizing Functionalized Boron Nitride Nanosheets

Dielectric polymer‐based composites with high breakdown strengths and thermal conductivities have attracted considerable attention when applied in electronic devices. In this study, a novel poly(m‐phenyleneisophthalamide) (PMIA) dielectric nanocomposite is successfully fabricated by introducing functionalized hexagonal boron nitride nanosheet (fBNNS) fillers. Due to effective functionalization of hexagonal boron nitride nanosheets (BNNSs), fBNNSs fillers are homogeneously dispersed in the PMIA matrix. The breakdown strength and thermal conductivity of PMIA/fBNNSs dielectric nanocomposite are investigated. Research results indicate that the breakdown strength of fBNNSs‐12 reaches 105.6 MV m^?1, which is 1.34 times that of pure PMIA. Moreover, owing to high thermal conductivity of fBNNSs, the thermal conductivities of fBNNSs‐12 are observably increased to 8.06 W m^?1 K of in‐plane direction and 0.84 W m^?1 K of through‐plane direction, respectively. Considering these properties, the manufactured PMIA/fBNNSs dielectric nanocomposites show potential applications in field of electronics.     

Scalable production of boron nitride nanosheets in ionic liquids by shear-assisted thermal treatment

Due to their intriguing properties, boron nitride nanosheets (BNNSs) with large lateral size and high crystallinity have great promise for many applications. However, the quantitative exfoliation of hexagonal boron nitride (h-BN) into good quality BNNSs still remains a key challenge. Herein, we report a scalable method to exfoliate BNNSs in ionic liquids (ILs) via shear-assisted thermal treatment. Few-layer BNNSs with well-preserved structural integrity are successfully prepared by this method. The synergistic effects of strong physical adsorption and intercalation of IL molecules, chemical interactions between hydrogen fluoride (HF) and h-BN, activation energy provided by heat treatment, and shear forces generated by repetitive stirring effect contribute to the exfoliation of BNNSs.     

Enhancing mechanical properties of fused silica composites by introducing well-dispersed boron nitride nanosheets

Well-dispersed boron nitride nanosheets (BNNSs) reinforced fused silica composites were successfully fabricated by surface modification assisted flocculation method. Surface modification can enhance the performance of flocculation process. BNNSs were homogeneously mixed with fused silica through the electrostatic interaction between hydroxylated BNNSs with negative charge and amino-modified fused silica with positive charge. The BNNSs can act as excellent nanofillers for enhancing the mechanical properties of fused silica composites. Approximately 74% and 48% increases in flexure strength and fracture toughness can be achieved for the 1.5 wt% BNNSs/fused silica composite, respectively. The toughening mechanisms were analyzed by microstructural characterization, especially for pull-out mechanism.     

Microstructure and mechanical properties of boron nitride nanosheets-reinforced fused silica composites

In order to overcome intrinsic brittleness and poor mechanical properties of fused silica (FS), boron nitride nanosheets (BNNSs) as a novel reinforcement were employed for fabrication of BNNSs/fused silica composites. BNNSs with micron lateral size were homogeneously dispersed with FS powder using a surfactant-free flocculation method and then consolidated by hot pressing. The flexural strength and fracture toughness of the composite with the addition of only 0.5 wt.% BNNSs increased by 53% and 32%, respectively, compared with those of pure FS. However, for higher BNNSs contents the improvement in mechanical properties was limited. Microstructural analyzes have shown that the toughening mechanisms are combinations of the pull-out, crack bridging, and crack deflection mechanisms.     

Boron nitride nanosheets reinforced glass matrix composites

The effect of reinforcing boron nitride nanosheets (BNNSs) on the mechanical properties of an amorphous borosilicate glass (BS) matrix was studied. The BNNSs were prepared using liquid exfoliation method and characterised by transmission electron microscopy, scanning electron microscopy and X-ray diffraction (XRD) analysis. The average length was ～0.5?μm, and thickness of the nanosheets was between 4 and 30 layers. These BNNSs were used to prepare BS-BNNS composite with different loading concentrations of 1, 2.5 and 5 mass-% (i.e. 1.395, 3.705 and 7.32 vol.-%). Spark plasma sintering (SPS) was used to densify these composites to avoid structural damages to the BNNSs and/or crystallisation within the composite sample during high temperature processing. The BNNSs were found to be evenly distributed in the composites matrix and were found to be aligned in an orientation perpendicular to the direction of the applied force in SPS. The mechanical properties including fracture toughness, flexural strength and elastic modulus were measured. Both fracture toughness and flexural strength increased linearly with increasing concentration of BNNSs in BS glass. There was an enhancement of ～45% in the fracture toughness (1.10?MPa.m^1/2) as well as flexural strength (118.82?MPa) with the addition of only 5 mass-% loading of BNNSs compared to BS glass (0.76?MPa.m^1/2; 82.16?MPa). The toughening mechanisms developed in the composites because of the reinforcement of BNNSs were thoroughly investigated.     

Fabricating boron nitride nanosheets from hexagonal BN in water solution by a combined sonication and thermal-assisted hydrolysis method

Boron nitride nanosheets (BNNSs) have unique and excellent thermal, electrical, and mechanical properties. But, their low efficiency in the production methods restricts their applications in the study of researchers. Hence, we reported a study in which BNNSs were successfully produced through a simple, affordable, and high-efficiency method. In this approach, hexagonal boron nitride block (h-BN) was firstly examined in aqueous solution under sonication (120 min) to produce hydroxyl functionalization and; furthermore, to penetrate water molecules between the layers. Then, with the explosion of the water molecules into the h-BN layers in the presence of heat, the space between the layers was increased. Finally, with the exfoliation of bulk h-BN layers through the ultrasonic irradiation, the ultrathin BNNSs were produced with an efficiency of 37%. The TEM and AFM images confirmed that the obtained BNNSs have mainly consisted of nanosheets with a thickness in the range of 3–8 nm. The results of UV–Vis analysis of BNNSs compared to h-BN showed a strong absorption peak at 204 nm^?1, which confirmed the presence of nanosheets. Also, other analyses, including XRD, BET, and FT-IR, confirmed the structure of BNNSs.