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.
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