113. Thermal Annealing Induced Enhancements of Electrical Conductivities and Mechanism for Multiwalled Carbon Nanotubes Filled Poly(Ethylene-co-Hexene) Composites
writer：Wenlin Li, Yaqiong Zhang, Jingjing Yang, Jun Zhang, Yanhua Niu, and Zhigang Wang
keywords：polyethylene, carbon nanotube, aspect ratio, network, diffusion, electrical conductivity
source：期刊
specific source：ACS Appl. Mater. Interfaces, 2012, 4 (12), 6468–6478
Issue time：2012年
通過電導率測量研究了多壁碳納米管填充的乙烯-己烯共聚物（MWCNT/PEH）復合材料在高于乙烯-己烯共聚物熔點的溫度下熱退火引起的導電性能增強行為。作為對比研究，將兩種具有不同長徑比（4和31）的多壁碳納米管混入PEH基體之中。利用SEM觀察了退火導致的多壁碳納米管/ PEH復合材料的形態變化。利用流變學測量清晰證實了多壁碳納米管在復合材料中形成的網絡結構。令人驚奇的是，具有較高多壁碳納米管濃度的多壁碳納米管/PEH復合材料的電導率在退火時間40分鐘后具有明顯增加，退火時間120分鐘后，電導率的增量最大接近3個數量級。分析得出多壁碳納米管/PEH復合材料導電率的增加取決于MWCNT含量、MWCNT的長徑比和退火時間。SEM結果表明，在退火后，微米級多壁碳納米管聚集體被破壞而形成更加松散多壁碳納米管網絡。不同類型的網絡結構決定了復合材料的流變學行為（MWCNT網絡和PEH鏈MWCNT聯合網絡）和導電性能（MWCNT管-管接觸網絡）的演變。而在退火過程中MWCNT網絡的重建，是由于在高溫下多壁碳納米管在PEH基體中發生了旋轉擴散，并且多壁碳納米管的長度對此行為具有顯著的影響。電導率的明顯增強可以歸因于熱退火過程中非布朗運動所誘導形成的松散網絡結構。
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.