Dielectric constant of fluids and fluid mixtures at criticality
Losada-Pérez, Patricia × Pérez-Sánchez, Germán Cerdeirina, Claudio A × Thoen, Jan #
Published by the American Physical Society through the American Institute of Physics
Physical Review E, Statistical, Nonlinear and Soft Matter Physics vol:81 issue:4
The behavior of the dielectric constant epsilon of pure fluids and binary mixtures near liquid-gas and liquid-liquid critical points is studied within the concept of complete scaling of asymmetric fluid-fluid criticality. While mixing of the electric field into the scaling fields plays a role, pressure mixing is crucial as the asymptotic behavior of the coexistence-curve diameter in the epsilon-T plane is concerned. Specifically, it is found that the diameters, characterized by a vertical bar T-T-c vertical bar(1-alpha) singularity in the previous scaling formulation [J.V. Sengers, D. Bedeaux, P. Mazur, and S. C. Greer, Physica A 104, 573 (1980)], gain a more dominant vertical bar T-T-c vertical bar(2 beta) term, whose existence is shown to be supported by literature experimental data. The widely known vertical bar T-T-c vertical bar(1-alpha) singularity of epsilon along the critical isopleth in the one-phase region is found to provide information on the effect of electric fields on the liquid-liquid critical temperature: from experimental data it is inferred that T-c usually decreases as the magnitude of the electric field is enhanced. Furthermore, the behavior of mixtures along an isothermal path of approach to criticality is also analyzed: theory explains why the observed anomalies are remarkably higher than those associated to the usual isobaric path.