Transport properties of the binary mixtures of the three organic liquids toluene, methanol, and cyclohexane

Abstract

We report on the measurements of diffusion (D), thermodiffusion (D T ) and Soret (S T ) coefficients in binary pairs of the ternary system toluene-methanol-cyclohexane using different instrumental techniques: microgravity measurements (SODI/DCMIX2) on the International Space Station (ISS), thermogravitational column (TGC) in combination with sliding symmetric tubes (SST), optical beam deflection (OBD), optical digital interferometry (ODI) and Counter Flow Cell (CFC). The binary systems have large regions where the mixtures are either not miscible or the Soret coefficient is negative. All the coefficients have been measured over a wide composition range with the exception of a miscibility gap. Results from different instruments and literature data are in favorable agreement over a broad composition range. Additionally, we have carefully measured the physical properties and the optical contrast factors (∂n/∂c) p,T and (∂n/∂T ) p,c . The latter ones were also calculated using the Looyenga equation. The measurements in methanol-cyclohexane mixture revealed a decay of the diffusion coefficient when approaching the miscibility gap. We have interpreted this in the spirit of the pseudospinodal concept.

Preliminary analysis of Diffusion Coefficient Measurements in ternary mIXtures 4 (DCMIX4) experiment on board the International Space Station

“…3(e), for this cell, after an abrupt negative variation of the phase difference due to the application of the thermal gradient, a positive variation occurs followed by a slower negative variation. These two variations of opposite directions are compatible with Soret coefficients of opposite sign, as expected for the polystyrene-toluene-cyclohexane mixture, since toluene-cyclohexane has a negative Soret coefficient [16] while polystyrene-toluene mixtures typi-cally show positive Soret coefficient [33]. In this case, even with only one wavelength, thanks to the well distinguishable dynamics, one can determine the two eigenvalues of the diffusion matrix of the ternary mixture.…”

“…The ternary mixture toluene-methanol-cyclohexane is of fundamental interest as it exhibits a miscibility gap and a large region with negative Soret coefficients. The transport and optical properties of binary subsystems were extensively examined [16]. It is known from statistical physics for binary mixtures and confirmed experimentally for methanol + cyclohexane mixture [17], that the diffusion coefficient D drastically diminishes approaching the binodal and should be zero at spinodal, while the thermodiffusion coefficient D T remains constant.…”

Do ternary liquid mixtures exhibit negative main Fick diffusion coefficients?

“…The first system is an almost ideal mixture, which is composed of tetralin (THN), isobutylbenzene (IBB) and dodecane (nC 12 ) [12,25]. For that system, the transport coefficients of its binary subsystems are also well-known [30][31][32]. The second system, composed of cyclohexane, toluene and methanol, exhibits a miscibility gap [27,28,33].…”

A ternary mixture at the border of Soret separation stability

“…[12][13][14][15][16] The second system, studied during DCMIX2 compaign, is composed of toluene, methanol, and cyclohexane. 13,[17][18][19] The DCMIX3 system is composed of water, ethanol, and triethylene glycol, 20 and the last campaign, DCMIX4, includes three additional mixtures of the system toluene, methanol, and cyclohexane; one mixture containing fullerene and a polymer diluted in a binary solvent. 21 The processing of the ISS data revealed that the final results were sensitive to the applied methodology.…”