The results of studies of static dielectric permittivity $\varepsilon \mathrm{}\left(T\right)\mathrm{}$ in the isotropic phase of 4-cyano-4-pentylalkylbiphenyl and $n-p-\mathrm{methoxybenzylidene}{-p}^{\prime }-\mathrm{butylaniline}$ (5CB-MBBA) mixtures are presented. 5CB and MBBA are nematogens with antagonistic permanent dipole moments configurations. An increase in MBBA concentration strongly decreases the pretransitional effect. However, a derivative analysis detected the existence of a pretransitional anomaly even if its weakness made a straightforward $\varepsilon \mathrm{}\left(T\right)\mathrm{}$ fit impossible. The obtained anomalies can be well portrayed by fluidlike equations, isomorphic to that applied in critical binary mixtures. Every time the same value of the specific heat critical exponent $\alpha \approx 0.5$ was obtained. A preliminary discussion of the influence of the permanent dipole configuration on the pretransitional behavior of dielectric permittivity was also possible.

• Received 14 May 2001

DOI:https://doi.org/10.1103/PhysRevE.64.051701