Concentration dependent refractive index of a binary mixture at high pressure

Fabrizio Croccolo (1) , Marc Alexandre Arnaud (2) , Didier Bégué (2) , Henri Bataller (1)

1 LFCR - Laboratoire des Fluides Complexes et leurs Réservoirs
2 IPREM - Institut des sciences analytiques et de physico-chimie pour l'environnement et les materiaux

In the present work binary mixtures of varying concentrations of two miscible hydrocarbons, 1,2,3,4-tetrahydronaphtalene (THN) and n-dodecane (C12), are subjected to increasing pressure up to 50 MPa in order to investigate the dependence of the so-called concentration contrast factor (CF), i.e., (n/c) p, T, on pressure level. The refractive index is measured by means of a Mach-Zehnder interferometer. The setup and experimental procedure are validated with different pure fluids in the same pressure range. The refractive index of the THN-C12 mixture is found to vary both over pressure and concentration, and the concentration CF is found to exponentially decrease as the pressure is increased. The measured values of the refractive index and the concentration CFs are compared with values obtained by two different theoretical predictions, the well-known Lorentz-Lorenz formula and an alternative one proposed by Looyenga. While the measured refractive indices agree very well with predictions given by Looyenga, the measured concentration CFs show deviations from the latter of the order of 6 and more than the double from the Lorentz-Lorenz predictions.

Mots clés: Refractive index; High pressure; Atmospheric pressure; Porous media; High pressure instruments

Domaines: Chimie-Physique [physics.chem-ph]

Fabrizio Croccolo, Marc Alexandre Arnaud, Didier Bégué, Henri Bataller. Concentration dependent refractive index of a binary mixture at high pressure. Journal of Chemical Physics, 2011, 135 (3), pp.Article number 034901. ⟨10.1063/1.3610368⟩. ⟨hal-00683950⟩