2026 年 21 巻 3 号 p. 26-00236
In this study, we extend the principle of frequency-domain Soret forced Rayleigh scattering (SFRS) to ternary mixtures for the determination of ternary Soret coefficients. We derived an analytical expression for the frequency-dependent phase lag in ternary systems, revealing the mathematical relationship between the measured phase lag and the coupled transport coefficients. Similar to time-domain SFRS, theoretical analysis demonstrates that the use of two-wavelength probe lasers enables the simultaneous determination of Soret and thermodiffusion coefficients. To validate the proposed theory, preliminary experiments were conducted on a ternary benchmark mixture composed of n-dodecane, isobutylbenzene, and 1,2,3,4-tetrahydronaphthalene using an existing single-wavelength probing setup. The measured frequency response was well-described by the derived analytical expression. This work provides a new foundation for characterizing mass transport in complex multicomponent mixtures that have remained challenging to investigate, by virtue of lock-in detection scheme offering minimal system disturbances and high robustness against scattered light.
