六方氮化硼高导热纳米材料:晶体结构、导热机理及表面修饰改性

Crystal Structure,Thermal Conductivity Mechanism and Surface Modification of High Thermal Conductivity Hexagonal Boron Nitride Nanomaterials

六方氮化硼(h-BN)纳米材料,如氮化硼纳米颗粒(BNNPs)、氮化硼纳米管(BNNTs)、氮化硼纳米纤维(BNNFs)、氮化硼纳米片(BNNSs),被认为是近年来最有前途的无机纳米材料。它们具有独特的理化性能,包括超宽带隙(5.0~6.0 eV)、高导热率(50~600 W/(m·K))、高机械强度等,在覆铜板(CCL)、电子封装(EMC)、热界面材料(TIMs)、发光二极管(LED)以及相变储能(PCMs)等领域具有广阔的应用前景。与其他功能材料一样,为改善其在聚合物复合材料中的分散性和界面亲和性,在其填充聚合物材料之前,通常要对其进行表面改性,最终达到改善聚合物复合材料的力学性能、导热性能及介电性能的目的。但由于h-BN特殊的晶体结构,使得其具有极强的化学惰性和抗氧化性,一方面,与石墨烯类似,每一个h-BN层中,B原子和N原子通过强共价键相连,但由于B和N的电负性不同,这种共价键具有类似离子键的特征,相比石墨结构中的C-C共价键,B-N键更强,更难以断裂。另一方面,不同于石墨片层间的AB型堆积,h-BN片层间为AA′型堆积,相邻层中B和N原子交替堆积产生“Lip-lip”作用,使得层间的极性相互作用强于石墨层间的范德华力。另外,h-BN在合成过程中,除了边缘上残留有痕量的-OH及-NH_(2)基团外,几乎没有其它官能团,极大加剧了h-BN表面修饰改性的难度。常用的碳纳米材料改性方法并不能使h-BN改性达到满意的效果,因此许多新的方法和药剂被用来设计修饰h-BN纳米材料。本文根据h-BN晶体结构、制备方法和表面性质,从共价键和非共价键功能化修饰两个方面,重点总结修饰改性药剂的设计选择以及对复合材料性能影响的研究进展,最后,对未来h-BN功能化的具体措施及修饰药剂设计选择的发展方向进行了展望。

Hexagonal boron nitride(h-BN)nanomaterials,such as boron nitride nano-particles,boron nitride nanotubes,boron nitride nanofibers and boron nitride nanosheets,have been among the most promising inorganic nanomaterials in recent years.Their unique properties,including high mechanical stiffness,wide band gap,excellent thermal conductivity and thermal stability,suggest many potential applications in various material fields,such as CCL,EMC,TIMS,LED and PCMs.Like other nanomaterials,prior to their utilization in nanocomposites,surface modification of h-BNs is often necessary in order to improve their dispersion and interfacial properties in polymer nanocomposites,so as to finally improve the mechanical properties,thermal conductivity and dielectric properties of polymer composites.However,the special crystals of h-BNs make it high chemical inertness and resistance to oxidation.First of all,similar to graphene,B atom and N atom are connected by strong covalent bond in each h-BN layer.However,due to the difference in electronegativity of B and N,the covalent bonds between B and N atoms are partially ionic,in contrast to the C-C bonds in graphitic structures,which makes the B-N bonds stronger and more difficult to break.Secondly,the peculiar stacking sequence of atomic planes of h-BNs are superposed as in AA′stacking sequence different from AB stacking sequence of graphite planes.The“Lip-lip”interactions caused by the alternating accumulation of B and N atoms in adjacent layers makes the polar interaction between layers stronger than the van der Waals force between graphite layers.In addition,h-BN has almost no functional groups except for the trace amount of hydroxyl groups and amino groups on the edge planes during the synthesis process,which greatly aggravates the difficulty of surface modification of h-BN.Therefore,many new methods and agents have been used to modify h-BN nanomaterials,because commonly used method for carbon nanomaterials to modify h-BN was not very successful.In this paper,on the basis of crystal structures,synthesis methods and surface properties of h-BN,the design and selection of modification agents and their influence on the performances of the composites are summarized with respect to covalent bond and non-covalent bond functional modification.At last,this review proposes concrete research approaches for h-BN functionali-zation and provides perspectives for the design and selection of modified agents.