Critical behavior of static properties for nitrobenzene-alkane mixtures

Liquid-liquid criticality in the dielectric constant and refractive index: A perspective

The critical region in the phase diagram of condensed matter systems such as fluids or fluid mixtures is characterized by the anomalous behaviour of specific thermodynamic properties. Here, we discuss the progress of understanding the behaviour of two intimately related properties, the dielectric constant [Formula: see text] and the refractive index n, when approaching the liquid-liquid critical point in binary liquid mixtures. Phenomenological scaling approaches, in particular, complete scaling formulation, are highlighted. In addition, experimental evidence provided by dielectric spectroscopy and optical measurements supporting the asymmetry-related critical features in [Formula: see text] and n in the one- and two-phase regions is assessed. We revisit recent experimental data and point out peculiar patterns of behaviour of polar-polar liquid mixtures as compared to (much more frequently studied) polar-non-polar mixtures. We point the necessity of additional research efforts towards the study of polar-polar mixtures, which would shed light into the influence of (microscopic) system-dependent parameters on asymmetry-related features of liquid-liquid criticality.

Heat capacity singularity of binary liquid mixtures at the liquid-liquid critical point

The critical anomaly of the isobaric molar heat capacity for the liquid-liquid phase transition in binary nonionic mixtures is explained through a theory based on the general assumption that their partition function can be exactly mapped into that of the Ising three-dimensional model. Under this approximation, it is found that the heat capacity singularity is directly linked to molar excess enthalpy. In order to check this prediction and complete the available data for such systems, isobaric molar heat capacity and molar excess enthalpy near the liquid-liquid critical point were experimentally determined for a large set of binary liquid mixtures. Agreement between theory and experimental results-both from literature and from present work-is good for most cases. This fact opens a way for explaining and predicting the heat capacity divergence at the liquid-liquid critical point through basically the same microscopic arguments as for molar excess enthalpy, widely used in the frame of solution thermodynamics.

Asymmetric criticality of the osmotic compressibility in binary mixtures

Heat capacities in the critical and the non-critical regions for {benzonitrile + tridecane} and {benzonitrile + pentadecane}, and light scattering for {benzonitrile + undecane}, {benzonitrile + dodecane}, {benzonitrile + tridecane}, {benzonitrile + tetradecane}, {benzonitrile + pentadecane}, and {benzonitrile + hexadecane} in the critical two-phase region were measured. Light scattering measurements confirmed the existence of the asymmetry for the osmotic compressibility while no such asymmetry was observed for the correlation length. An analysis of the osmotic compressibility asymmetry suggested the dominance of the singular term |ΔT[circumflex]|(β), which supports the complete scaling theory. The consistency of the complete scaling theory in descriptions of different asymmetry behaviors was also discussed. Moreover, it was found that the contribution of the heat capacity-related term is also important in describing the asymmetry of the osmotic compressibility as it was observed in studies of the diameters of the coexistence curves.

Electric permittivity anomaly close to the critical consolute point of a nitrobenzene + octane liquid mixture

Electric permittivity and density were measured in a nitrobenzene and octane mixture in the vicinity of the upper critical consolute point. Measurements were conducted in the one-phase region, at the critical concentration. The possibility of stirring in the course of measurements allowed us to check if the density and concentration gradients had any influence on the obtained results. No signs of the presence of the gradients mentioned above were found. Using the data obtained in the reported measurements, different methods of the fitting of the equation describing the permittivity anomaly were tested. The calculation of a reliable value of the critical amplitude, used to estimate the critical temperature shift under the influence of the electric field, was of particular interest. The derivative (∂T(c)/∂E(2)) was found to be (-3.9 ± 0.3) × 10(-16) K m(2) V(-2).

Comparison of complete scaling and a field-theoretic treatment of asymmetric fluid criticality

We investigate the connection between the theory of complete scaling and a field-theoretic (FT) treatment of asymmetric fluid criticality. To facilitate the comparison, we develop an equation of state from a simplified form of the complete scaling transformations and systematically compare this equation of state with the equation of state generated by a FT treatment of an asymmetric Landau-Ginzburg-Wilson Hamiltonian. We find, with care in interpretation, that these two approaches may be read as equivalent up to terms involving an independent higher-order asymmetric correction-to-scaling exponent.