Abstract-Investigation of Dielectric Properties of Polymers and their Discrimination Using Terahertz Time-Domain Spectroscopy with Principal Component Analysis

Muhammad Mumtaz, Ahsan Mahmood, Sabih D. Khan, M. Aslam Zia, Mushtaq Ahmed, and Izhar Ahmad

https://www.osapublishing.org/as/abstract.cfm?uri=as-71-3-456&origin=search

Polymers are among the most commonly used materials in our everyday life. They are generally transparent to terahertz (THz) radiation, but are quite difficult to differentiate using optical techniques as few or no characteristic features exist in the spectral range of <2.0 THz for small and portable radiation systems. In this work, we report experimental measurement of refractive indices and absorption coefficients of styrene acrylonitrile (SAN) and Bakelite in the spectral range of 0.2–2.0 THz for the first time. Additionally, we demonstrate that by combining principle component analysis (PCA) with THz time-domain spectroscopy one can differentiate such polymers. In this analysis, the first three principle components PC1, PC2, and PC3 depict >94% variance with a distribution of 72.45%, 11.52%, and 9.38%, respectively.

Abstract-Dielectric Properties of Ethanol and Gasoline Mixtures by Terahertz Spectroscopy and an Effective Method for Determination of Ethanol Content of Gasoline

Enis Arik , Hakan Altan , and Okan Esenturk

http://pubs.acs.org/doi/abs/10.1021/jp500760t

J. Phys. Chem. A, Just Accepted Manuscript

DOI: 10.1021/jp500760t

Publication Date (Web): April 4, 2014

Copyright © 2014 American Chemical Society

Investigation of frequency dependent permittivity of mixture solutions provides information on role of intermolecular interactions on relaxation processes of solvent and solute molecules. In this study the dielectric properties of ethanol/gasoline mixtures in the terahertz spectral region are investigated. Frequency dependent absorption coefficients, refractive indices, and complex permittivities of pure ethanol and gasoline, and their mixtures at varying ethanol volume percentages (v/v %) are reported. As the mixing ratio changes meaningful shifts are observed in the frequency dependent refractive index and absorption coefficients associated with the dominant component, ethanol. The relaxation dynamics of the pure gasoline and ethanol are successfully modelled with Debye model using ultrafast nature of the terahertz transients, and those of mixture solutions are investigated by an additive model with an assumption of minimum interaction due to the significant differences in their molecular natures; polar and nonpolar. Successful modelling of the mixtures confirms the weak interaction assumption and enables to accurately determine the ethanol content. Among five ethanol/gasoline blends, except for one mixture, the estimated percent ethanol in gasoline are predicted with an accuracy of ca. 1% with respect to the actual ethanol percentage. In addition, the results show that free OH contribution to the macroscopic polarization is significantly higher at low concentrations (5-20%) and lower at 50% compared to the pure ethanol. The measurements and analysis presented here show that time-domain terahertz studies can offer invaluable insight into development of new models for polar/nonpolar complex mixture solutions.