title: Concentration dependent refractive index of CO2/CH4 mixture in gaseous and supercritical phase.
abstract: Carbon dioxide (CO2)/methane (CH4) binary mixtures are investigated at pressure values up to 20 MPa at 303 K in order to investigate the pressure dependence of the optical concentration contrast factor, ∂n/∂c(P,T), through gaseous and supercritical phase. Refractive index is measured by means of a Michelson interferometer. Refractivities of the mixtures are found in good agreement with Lorentz-Lorenz predictions after density calculations by means of the AGA8-DC92 equation of state. Experimental polarizabilities of pure fluids are compared to quantum calculations of monomers and dimers for each pressure; it results that the quantity of dimers is small in the investigated thermodynamic conditions. Finally, by extending our experimental database with numerical simulations, we evidence that ∂n/∂cP,T presents a critical enhancement similar to heat capacity.
authors.affiliation: Laboratoire des Fluides Complexes et leurs Réservoirs - UMR 5150, CNRS, Université de Pau et des Pays de l'Adour, 64600 Anglet, France.
authors.forename: C
authors.initials: C
authors.lastname: Giraudet
authors.affiliation: Atelier de Physique Générale, Université de Pau et des Pays de l'Adour, BP 1155, 64013 Pau Cedex, France.
authors.forename: L
authors.initials: L
authors.lastname: Marlin
authors.affiliation: Institut Pluridisciplinaire de Recherche sur l'Environnement et les Matériaux - UMR 5254, CNRS, Université de Pau et des Pays de l'Adour, BP 1155, 64013 Pau Cedex, France.
authors.forename: D
authors.initials: D
authors.lastname: Bégué
authors.affiliation: Laboratoire des Fluides Complexes et leurs Réservoirs - UMR 5150, CNRS, Université de Pau et des Pays de l'Adour, 64600 Anglet, France.
authors.forename: F
authors.initials: F
authors.lastname: Croccolo
authors.affiliation: Laboratoire des Fluides Complexes et leurs Réservoirs - UMR 5150, CNRS, Université de Pau et des Pays de l'Adour, 64600 Anglet, France.
authors.forename: H
authors.initials: H
authors.lastname: Bataller