Stepwise Percolation: Identification of New Behavioral Mechanism of Conductive Polymer Composites
Professor Jung Tae Lee’s research team at the Department of Plant and Environmental New Resources has identified Stepwise Percolation, a new mechanism theory for conductive polymer composites (CPCs)
A joint research team led by Professor Jung Tae Lee at the Department of Plant and Environmental Materials Engineering and Professor Kim Seong Yun Kim at the Department of Organic Materials and Textile Engineering of Jeonbuk National University identified the Stepwise Percolation, a new prediction model for the electrical properties of conductive polymer composites. Related research results were published in the international journal Materials Today Physics (IF: 11.5) under the title, “Stepwise percolation behavior induced by nano-interconnection in electrical conductivity of polymer composites.”
Nanocarbons such as carbon nanotubes and graphene are attracting attention as fillers for next-generation conductive composites. While the behavior of conductive polymer composites is generally explained by percolation theory, the electrical conductivity of new CPCs using a continuous nanocarbon filler network has exceeded the predictions of a conventional percolation model without a clear identification of its mechanism.
Experimental proof of stepwise percolation theory
The research team developed an in situ polymerization method using heat convection from an air fryer and fabricated a conductive polymer composite (CPC) with high filler content up to 50% in volume incorporating continuous nanocarbon filler networks. With the new CPC, the team identified the mechanism that enables the improved conduction properties of a CPC containing continuous fillers in the sense that there is a secondary percolation after the primary percolation. This discovery led to a novel behavioral prediction model based on the newly identified mechanism, which was given the name “stepwise percolation model.”
When the tunneling resistance effect of electrons generated in the CPC was reduced by direct physical contact with the filler, the movement speed of electrons was improved, and the CPC containing continuous nanocarbon fillers showed improved conductive properties. The research team confirmed this experimentally and also found that these characteristics can be predicted based on the proposed stepwise percolation model.
The CPC fabricated by the research team consistently demonstrated significantly higher level of electrical performance after the secondary percolation. Its electrical conductivity was 4086S/m (3828% increase at 40 vol% multi-walled carbon nanotube [MWCNT] compared to 35 vol%), electromagnetic interference shielding performance at 50 dB (236.36% increase at 40 vol% graphene nanoplatelet relative to 25 dB at 35 vol%), and 82.22% humidity sensing properties at 50vol% (compared to 47.13% at 35 vol% MWCNT), compared to CPCs with lower levels of continuous nanocarbon fillers.
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