Terahertz Time-Domain Spectroscopy of Graphene Nanoflakes Embedded in Polymer Matrix
Terahertz Time-Domain Spectroscopy of Graphene Nanoflakes Embedded in Polymer Matrix
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DOI：
10.3390/app9030391
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发表时间：
2019-02-01
影响因子：
2.7
通讯作者：
Sobolewski, Roman
中科院分区：
文献类型：
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作者：
Koroliov, Anton;Chen, Genyu;Sobolewski, Roman
利用太赫兹时域光谱（THz-TDS）技术，获得了含有可控量剥离石墨烯的聚合物纳米复合材料的透射太赫兹辐射光谱。本研究中使用的石墨烯纳米复合材料（1 wt%）是基于聚对苯二甲酸乙酯-乙烯二烯油酸酯（PET-DLA）基体，并通过千级（适合研发和原型制作）原位聚合制备的。接下来是压缩成型成0.3毫米厚和0.9毫米厚的箔片。透射电子显微镜（TEM）和拉曼光谱研究证实了分散在聚合物基体中的石墨烯纳米片由几层石墨烯组成。使用低温生长的GaAs光导发射器和探测器产生和检测太赫兹辐射瞬态，两者都由由Ti：蓝宝石激光器以76 mhz重复频率产生的100 f宽，800 nm波长的光脉冲激发。时域信号通过氮、整齐聚合物和1 wt%石墨烯-聚合物纳米复合材料样品传输，随后通过快速傅里叶变换转换到谱域。我们的光谱仪的光谱范围高达4太赫兹，测量是在室温下干燥的氮环境中进行的。我们收集了一系列光谱，并基于菲涅耳方程进行了数值分析，这使我们能够提取太赫兹频率范围内的折射率和吸收系数，以及它们与样品成分和石墨烯含量的关系。利用Clausius-Mossotti关系，我们还成功地估计了石墨烯的有效介电常数等于类似于7 +/- 2。最后，我们从实验数据中提取了石墨烯纳米复合材料的复杂电导率谱，并成功地将其拟合到Drude-Smith模型中，证明了我们的石墨烯纳米片在聚合物基体中被隔离，并表现出高度局域的电子后向散射，具有飞秒弛豫时间。我们的研究结果揭示了剥离的石墨烯纳米片如何在太赫兹频率范围内改变聚合物的电学性能。重要的是，他们证明了复合电导率分析是一种非常有效的、宏观的、非破坏性的（与TEM相反）工具，用于表征石墨烯纳米填料在共聚酯基体中的分散。
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-f s-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 similar 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.