Diffusion, thermal diffusion, and Soret coefficients and optical contrast factors of the binary mixtures of dodecane, isobutylbenzene, and 1,2,3,4-tetrahydronaphthalene.

We have measured the Soret (S(T)), diffusion (D), and thermal diffusion (D(T)) coefficients of the three binary benchmark mixtures of dodecane (C12), isobutylbenzene, and 1,2,3,4-tetrahydronaphthalene at T = 25°C for at least five different concentrations each, covering the entire binary composition range. The two different optical techniques employed, optical beam deflection and optical digital interferometry, are in good to excellent agreement. Additionally, we have carefully measured the optical contrast factors (∂n/∂c)(p, T) and (∂n/∂T)(p, c). If the temperature and composition dependence of the mixture density is taken into account, both the Lorentz-Lorenz (LL) and the Looyenga (LO) equations give reasonable predictions of (∂n/∂c)(p, T). In case of (∂n/∂T)(p, c), only the LO equation yields good predictions in case of constant molecular polarizabilities α(i) of the pure compounds. If the apparent temperature dependence of α(i) is explicitly taken into account, excellent predictions are obtained both from the LL and the LO equations.