Critical behavior of the binary fluids cyclohexane-methanol, deuterated cyclohexane-methanol and of their isodensity mixture: Application to microgravity simulations and wetting phenomena

It is possible to adjust the density of cyclohexane by adding a small amount of deuterated cyclohexane. Then the mixture deuterated cyclohexane-cyclohexane-methanol can be made isopycnic. We have determined the critical properties of this system and of the systems cyclohexane-methanol and deuterated cyclohexane-methanol: coexistence curve, correlation length, and osmotic compressibility via refractive index and turbidity measurements. For that purpose, a detailed discussion of the validity of the volume additivity and of the Lorentz-Lorenz formula has been made. The main result is that the isopycnic system acts as a binary mixture for the phase transition properties as shown by the \ensuremath{\beta} exponent and the amplitude combinations (${R}_{\ensuremath{\xi}}^{+}$${R}_{c}^{\mathrm{\ensuremath{-}}1/3}$) which exhibit the universal values. Some aspects of microgravity conditions can then be created. We have studied in the isopycnic system the phase separation at critical concentration; new features are found after a thermal quench: macroscopic spinodal decomposition structures during the phase separation process and macroscopic wetting layers in the final equilibrium state.