JunhHua WU
材料科学技术（英）
Microwave dielectric measurements over the broad bandwith of 10 MHz to 20 GHz were conducted on composites comprising bundles of single-walled carbon nanotubes (SWNT) embedded in an epoxy matrix, in comparison to the nano-graphite and MWNT. It is found that both relative real and imaginary permittivity of the nanocomposites are strong functions of the SWNT concentration, showing large, wide dielectric and electrical response. Distinct resonance around 1.5 GHz is observed at high SWNT concentrations, accompanied by the downshift of the resonance frequency with increasing concentration. Largely, the SWNT-epoxy composites share the behavior of the MWNT owing to structural similarity, much more effective than the nano-graphite. The remarkable, broadband dielectric and electrical properties of the nanotubes acquired in the work originate from their unique seamless graphene architectures, modeled by two major contributions, dielectric relaxation/resonance and electronic conduction, which is substantiated by the agreement between theoretical analysis and experimental results. The carbon nanotube composites are prospective for microwave applications and offer experimental evidence for fundamental studies in low-dimensional systems.
关键词:
Single-walled carbon nanotube
,
carbon
,
nanotube
,
Dielectric
谌为
,
李峰
,
刘畅
,
尹利长
新型炭材料
doi:10.1016/S1872-5805(16)60030-6
采用密度泛函理论计算系统研究了单壁碳纳米管( Single-walled carbon nanotube,SWCNT)改变手性外延生长(手性指数从(n,m)变化到(n±△,m芎△),其中△=1和2)的热力学过程。结果表明,碳管手性变化后外延生长在热力学上都需要吸收能量,其所需吸收的能量随着管径的减小线性减小。在△=1的情况下,由于近扶手椅型碳管改变手性时,所引入的5~7元环对与管轴的夹角比近锯齿型碳管更大,导致5~7元环对的形成能增加,使得管径相同的近扶手椅型碳管比近锯齿型碳管在改变手性生长时需要吸收更多的能量。在△=2的情况下,发现只有当两个必须引入的5~7元环对相互毗邻,手性改变的外延生长所需能量最小,预测其为实验上最易于实现的碳管手性指数由( n,m)变化到( n±△,m芎△)的外延生长模式。这些理论研究结果有助于深入理解SWCNTs手性变化后外延生长的热力学行为,可为基于外延生长可控制备单一手性SWCNTs提供理论依据。
关键词:
单壁碳纳米管
,
手性变化
,
5~7缺陷
,
外延生长
,
密度泛函理论
