Fickian and thermal diffusion coefficients of binary mixtures of isobutylbenzene and n -alkanes at different concentrations from the optical beam deflection technique

Abstract

We report the Fickian diffusion (D12), thermal diffusion (DT), and Soret (ST) coefficients of 4 binary mixtures of isobutylbenzene (IBB) and n-alkanes (n-hexane, n-octane, n-decane, and n-dodecane) at 298.15 K and atmospheric pressure. The concentration is varied in the whole range. The Optical Beam Deflection technique is used in the measurements. We first verify our measurements with published data. The concepts of molecular similarity and mobility are invoked to investigate D12 and DT dependency on molecular weight and concentration. Our analysis reveals a combined effect of molecular mobility and similarity dependency of DT on concentration and molecular weight of the n-alkanes. The mobility of individual molecules describes the D12 dependency on concentration and molecular weight of alkanes. The dependency of D12 on concentration weakens as the n-alkane molecular weight increases. DT increases with IBB concentration for nC6 and nC8 and decreases with IBB concentration for nC10 and nC12. In this work, we demonstrate that the temperature contrast factors can be accurately estimated without the use of an interferometer.