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 $\epsilon \text{—}T$ plane is concerned. Specifically, it is found that the diameters, characterized by a ${\left|T-T_c\right|}^{1-\alpha }$ 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 ${\left|T-T_c\right|}^{2\beta }$ term, whose existence is shown to be supported by literature experimental data. The widely known ${\left|T-T_c\right|}^{1-\alpha }$ 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.

• Received 3 February 2010

DOI:https://doi.org/10.1103/PhysRevE.81.041121