Metal-insulator transition and size dependent electrical percolation in onion-like carbon/polydimethylsiloxane composites

Abstract

Dielectric/electric properties of onion-like carbon (OLC)/polydimethylsiloxane composites were investigated over very wide frequency (20 Hz–3 THz) and temperature (26–500 K) ranges. The percolation threshold in these composites strongly dependents on the OLC aggregate sizes and was lowest for the composites with the smallest OLC aggregate sizes (∼40 nm). Interestingly, the transition into the insulator state of the composites occurred at higher temperatures. The transition temperature increases with OLC aggregate concentration. Above the percolation threshold, the electrical conductivity in the composites occurs mainly due to electron tunneling between OLC clusters and quasi-one-dimensional hopping inside the clusters. The hopping almost vanishes at frequencies above 100 GHz where the phonon contribution dominates.

Carbon-Coated Nickel Nanoparticles: Effect on the Magnetic and Electric Properties of Composite Materials

“…Next, the system was placed into a vacuum to remove isopropanol from the mixture. Curing of the PDMS-nanoparticle mixture at 60 • C for 2 h and 40 • C overnight resulted in films with good nanoparticle dispersion (see Figure 1) [33]. Samples with 1, 5, 7, 9, and 11 vol % of Ni@C dispersed in PDMS were prepared.…”

Size‐Dependent Electrical and Thermal Properties of Onion‐Like Carbons/Polyurethane Composites

“…The percolation threshold value close to 5.4 vol. % for small‐sized OLC is slightly lower than the percolation threshold observed in OLC/polydimethylsiloxane composites for the same aggregate size . The huge values of dielectric permittivity and electrical conductivity in the microwave range (e.g.…”

“…The aggregate structure of conductive particles thus has a strong impact on the threshold and on the related composite dielectric/electrical properties [17], as already observed for some carbon black composites [17]. OLCs, similarly to carbon blacks, may indeed have a complex aggregate structure [7] and it was found that, in OLCpolydimethylsiloxane composites, the percolation threshold is the lowest with the smallest OLC aggregates [19].…”

A phantom study of terahertz spectroscopy and imaging of micro- and nano-diamonds and nano-onions as contrast agents for breast cancer

“…While a single layer of microdiamonds in PDMS does not fully model the distributed particles that would be present in a biomedical application, it is still useful to observe the THz signal interaction with the particles. Additional details on the fabrication of particles and sample preparation were previously reported in other works [32],[37],[39],[53]. …”