Dielectric Properties of Carbon-Materials-Filled Composites Characterized by Terahertz Time-Domain Spectroscopy

Abstract

The optical properties of composites, formed by filling the high density polyethylene (HDPE) with carbon black (CB), multi-walled carbon nanotubes (MWNTs) and fullerene (C60), respectively, in the frequence region from 0.3 to 2.0 terahertz (THz) were characterized with THz time-domain spectroscopy (THz-TDS). It is found that the optical parameters and the details of their variation with frequence and filler concentration are significantly different for different kinds of carbon materials. The MWNTs filled composites have the biggest absorption coefficient value, refractive index and real conductivity. The C60/HDPE composite shows very little changes in absorption and refractive index compared to that of the HDPE even at a filler-content of 12.3% in volume fraction. These phenomena are related to the special properties of the fillers as well as their particulate structures, such as aspect ratio, particle size, and aggregate structure, etc. The results are analyzed by using Cole-Cole theory of dipole relaxation under the assumption that carbon particles dispersed in the matrix behave like dipoles.

Terahertz Shielding Properties of Carbon Black Based Polymer Nanocomposites

“…The absorption coefficient values grow thrice as much with growing filler loading at 1.5 THz than they do at 0.5 THz. Absorption coefficient values reported in this work are consistent with data on similar materials found in the literature, for example a HDPE/CB composite reaches over 100 cm −1 value at 15 vol% CB loading, while a polypropylene-based composite enhanced with multiwalled carbon nanotubes shows maximum absorption coefficient of ~80 cm −1 at 1.4 THz, which also exhibits growth trend with changing frequency [36,37].…”

Terahertz time-domain spectroscopy as a novel metrology tool for liquid-phase exfoliated few-layer graphene

“…As a consequence, THz-TDS yields directly the amplitude and the phase of each spectral component, making it possible to obtain unambiguously the refractive index and absorption coefficient, and therefore the complex permittivity of the sample [36]. As non-polar polymers are transparent to THz frequencies [38], THz-TDS is well suited to the characterisation of FLG-polymer composites [39] of this type. Absorption of THz radiation is largely the result of the motion of free-charge carriers in conductors and semiconductors, and activation of phonon modes in dielectrics such as polymers.…”

Characterizations of high-density polyethylene by terahertz time-domain spectroscopy

“…Terahertz time-domain spectroscopy (THz-TDS) has become an important tool for identifying material components and analyzing material characteristics [13][14][15][16] owing to its advantages of being non-contact, non-invasive, strong penetrability and high sensitivity [17][18][19]. HDPE is often used and tested as a substrate material in the terahertz range [20,21], Stefan Sommer et al [22] distinguished the crystalline state of HDPE by refractive index, and the adsorption characteristics of HDPE have been studied by Gas chromatography [8], liquid chromatography [23,24], etc. But the research on optical properties of HDPE composites and adsorption is rare in the terahertz range.…”