Percolation nanostructured materials

S, Zavyalov, A, Timofeev, A. Pivkina, and J. Schoonman, Metal-polymer nanocomposites formation and properties near the percolation threshold in Nanostructured Materials Selected... 

Another area of intense interest in conducting-polymer nanomaterials for chemical sensing is their combination with carbon nanostructures, most particularly carbon nanotubes, either single-walled (SWNT) or multiwaUed (MWNT). This again reflects the desire to combine the beneficial properties of both types of material to create new combinations with novel properties. CNTs empart high conductivity and high aspect ratios, which yield low percolation thresholds with nanodimensional stmctural order. This has led to their application as chemical sensors. However, CNT-based devices are difficult to fabricate, an issue which may be overcome by their dispersion in a conductive polymeric matrix. 

It is well known that the percolation threshold is strongly dependent on the aspect ratio. One-dimensional (ID) nanostructures, such as nanowires, nanotubes, and nanoribbons, have geometries that are favorable for the maintenance of connectivity at low content of active materials. Carbon nanotubes (CNTs) are a good representative example. Electrical percolation can be achieved in polymer composites with well-dispersed single-walled carbon nanotubes (SWCNTs) at levels as low as 0.03 wt% [69]. Recently, it has been reported that the formation of semiconducting nanofibers facilitates percolation in semiconducting/insulating polymer blends. 

At the same time, Peddini et al. described the preparation of nanocomposites from styrene-butadiene mbber (SBR) and multiwall carbon nanotubes (MWCNT). MWCNT are important nanostructures due to the exceptionally high modulus and aspect ratios there has been much interest in using them as reinforcing agents for polymer composites. Styrene-butadiene rubber (SBR), commonly used as a tread stock for tires, is employed here as the matrix for creation of a masterbatch with oxidized MWCNT (12.3-15 wt%). These materials do not show a high level of electrical conductivity as might be expected from a percolation concept, signifying excellent tube dispersion and formation of a bound rubber layer on the discrete MWCNT [126]. 

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