CAS Key Laboratory of Soft Matter Chemistry, Department of Polymer Science and Engineering, University of Science and Technology of China, Hefei, Anhui Province 230026, PR China.
ACS Appl Mater Interfaces. 2012 Dec;4(12):6468-78. doi: 10.1021/am302597f. Epub 2012 Dec 4.
Thermal annealing-induced enhancements of electrical conductivities at the temperature higher than the melting point of poly(ethylene-co-hexene) matrix for multiwalled carbon nanotubes filled poly(ethylene-co-hexene) (MWCNTs/PEH) composites were investigated by electrical conductivity measurements. Two types of MWCNTs with low and high aspect ratios (4 and 31) were added as fillers into PEH matrix, respectively for comparison study purpose. The morphological changes due to annealing for MWCNTs/PEH composites were observed by SEM. The formation of MWCNT networks in the composites were clearly demonstrated by rheological measurements. It is surprisingly found that the electrical conductivity for MWCNTs/PEH composites with high MWCNT concentrations increases obviously with annealing time of 40 min and the maximum increment approaches about 3 orders of magnitude with annealing time of 120 min. The increase of electrical conductivity of MWCNTs/PEH composites depends on MWCNT content, MWCNT aspect ratio and annealing time. SEM results clearly reveal that micrometer-sized MWCNT aggregates are broken down and more loosely packed MWCNT networks form due to annealing. Different types of networks in the composites are responsible for the evolutions of rheological (MWCNT network and PEH chain-MWCNT combined network) and electrical conductivity properties (tube-tube contacting MWCNT network). The reconstruction of MWCNT network during annealing is attributed to rotational diffusion of MWCNTs in PEH matrix at high temperature and the length of MWCNTs shows significant effect on this. The obvious enhancements of electrical conductivities can be ascribed to the thermal annealing-induced formation of loosely packed more homogeneous networks through non-Brownian motions.
通过电导率测量研究了多壁碳纳米管填充聚乙烯-共-己烯（MWCNTs/PEH）复合材料在高于聚合物基体熔点的温度下热退火诱导电导率增强的现象。分别添加了两种低长径比（4 和 31）和高长径比（4 和 31）的 MWCNTs 作为填充剂，以进行对比研究。通过 SEM 观察了 MWCNTs/PEH 复合材料因退火引起的形态变化。通过流变学测量清楚地证明了复合材料中 MWCNT 网络的形成。令人惊讶的是，发现具有高 MWCNT 浓度的 MWCNTs/PEH 复合材料的电导率随着退火时间的增加 40 分钟而明显增加，最大增量在 120 分钟的退火时间内接近 3 个数量级。MWCNTs/PEH 复合材料电导率的增加取决于 MWCNT 含量、MWCNT 长径比和退火时间。SEM 结果清楚地表明，由于退火，微米级 MWCNT 聚集体被分解，形成更疏松的 MWCNT 网络。复合材料中不同类型的网络负责流变学（MWCNT 网络和 PEH 链-MWCNT 复合网络）和电导率性能（MWCNT 管-管接触网络）的演变。MWCNT 网络在退火过程中的重建归因于 MWCNTs 在高温下的旋转扩散，并且 MWCNTs 的长度对其有显著影响。电导率的明显增强可归因于热退火诱导通过非布朗运动形成疏松的更均匀的网络。
