The experimental results of isothermal pressure dielectric permittivity ɛ studies in a critical mixture characterized by a negative shift of critical temperature induced by pressure ${(dT}_C/dP<\mathrm{}0)$ are presented. The critical effect is portrayed by the same relation as in previous $\varepsilon \mathrm{}\left(T\right)\mathrm{}$ and $\varepsilon \mathrm{}\left(P\right)\mathrm{}$ studies, with the critical exponent $\alpha =0.12\mathrm{}\pm \mathrm{0.03.}$ The advantage of pressure studies is the negligible influence of the correction-to-scaling term and the low-frequency Maxwell-Wagner effect. This conclusion is supported by the distortion-sensitive derivative analysis of the experimental data. In contrast to previous $\varepsilon \mathrm{}\left(P\right)\mathrm{}$ studies, carried out in mixtures with ${\mathrm{dT}}_C/dP>\mathrm{}0,$ the critical effect manifests by the bending-up behavior near the critical point. It is suggested that signs of the critical amplitudes of $\varepsilon \mathrm{}\left(P\right)\mathrm{}$ and $\varepsilon \mathrm{}\left(T\right)\mathrm{}$ anomalies may be related to the excess volume $V^E$ and the excess enthalpy $H^E,$ respectively.

• Received 7 December 2000

DOI:https://doi.org/10.1103/PhysRevE.64.061104