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Terahertz Time-Domain Spectroscopy of Graphene Nanoflakes Embedded in Polymer Matrix

Terahertz Time-Domain Spectroscopy of Graphene Nanoflakes Embedded in Polymer Matrix

Title: Terahertz Time-Domain Spectroscopy of Graphene Nanoflakes Embedded in Polymer Matrix
Author: Koroliov, Anton
Chen, Genyu
Goodfellow, Kenneth M.
Vamivakas, A. Nick
Staniszewski, Zygmunt
Sobolewski, Peter
Fray, Mirosława El
Łaszcz, Adam
Czerwinski, Andrzej
Richter, Christiaan   orcid.org/0000-0002-6563-4923
... 1 more authors Show all authors
Date: 2019-01-23
Language: English
Scope: 391
University/Institute: Háskóli Íslands
University of Iceland
School: Verkfræði- og náttúruvísindasvið (HÍ)
School of Engineering and Natural Sciences (UI)
Department: Iðnaðarverkfræði-, vélaverkfræði- og tölvunarfræðideild (HÍ)
Faculty of Industrial Eng., Mechanical Eng. and Computer Science (UI)
Series: Applied Sciences;9(3)
ISSN: 2076-3417
DOI: 10.3390/app9030391
Subject: Drude-Smith model for complex conductivity; Graphene; Graphene nanoflakes; Graphene-polymer nanocomposites; Multiblock copolyesters; Terahertz time-domain spectroscopy; Nanótækni; Litrófsgreining
URI: https://hdl.handle.net/20.500.11815/1843

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Koroliov, A.; Chen, G.; Goodfellow, K.M.; Vamivakas, A.N.; Staniszewski, Z.; Sobolewski, P.; Fray, M.E.; Łaszcz, A.; Czerwinski, A.; Richter, C.P.; Sobolewski, R. Terahertz Time-Domain Spectroscopy of Graphene Nanoflakes Embedded in Polymer Matrix. Applied Sciences 2019, 9, 391.


The terahertz time-domain spectroscopy (THz-TDS) technique has been used to obtain transmission THz-radiation spectra of polymer nanocomposites containing a controlled amount of exfoliated graphene. Graphene nanocomposites (1 wt%) that were used in this work were based on poly(ethylene terephthalate-ethylene dilinoleate) (PET-DLA) matrix and were prepared via a kilo-scale (suitable for research and development, and prototyping) in-situ polymerization. This was followed by compression molding into 0.3-mm-thick and 0.9-mm-thick foils. Transmission electron microscopy (TEM) and Raman studies were used to confirm that the graphene nanoflakes dispersed in a polymer matrix consisted of a few-layer graphene. The THz-radiation transients were generated and detected using a low-temperature-grown GaAs photoconductive emitter and detector, both excited by 100-fs-wide, 800-nm-wavelength optical pulses, generated at a 76-MHz repetition rate by a Ti:Sapphire laser. Time-domain signals transmitted through the nitrogen, neat polymer reference, and 1-wt% graphene-polymer nanocomposite samples were recorded and subsequently converted into the spectral domain by means of a fast Fourier transformation. The spectral range of our spectrometer was up to 4 THz, and measurements were taken at room temperature in a dry nitrogen environment. We collected a family of spectra and, based on Fresnel equations, performed a numerical analysis, that allowed us to extract the THz-frequency-range refractive index and absorption coefficient and their dependences on the sample composition and graphene content. Using the Clausius-Mossotti relation, we also managed to estimate the graphene effective dielectric constant to be equal to ~7 ± 2. Finally, we extracted from our experimental data complex conductivity spectra of graphene nanocomposites and successfully fitted them to the Drude-Smith model, demonstrating that our graphene nanoflakes were isolated in their polymer matrix and exhibited highly localized electron backscattering with a femtosecond relaxation time. Our results shed new light on how the incorporation of exfoliated graphene nanoflakes modifies polymer electrical properties in the THz-frequency range. Importantly, they demonstrate that the complex conductivity analysis is a very efficient, macroscopic and non-destructive (contrary to TEM) tool for the characterization of the dispersion of a graphene nanofiller within a copolyester matrix.


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