Critical heat capacity variation at the smectic A1–smectic A2 transition

Abstract
A high resolution a.c. calorimetric study has been carried out on a mixture of 4-n-hexylphenyl-4′-(4″-cyanobenzoyloxy)benzoate (DB6) and terephthalylidene-bis-(4-n-butylaniline) (TBBA). The heat capacity at the smectic A1—smectic A2 (SA1-SA2) transition in a DB6 + 15 per cent TBBA mixture exhibits a distinct cusp with a critical exponent α ⋍ -0.15. This value for a is consistent with the critical correlation exponent v obtained from X-ray scattering, but it does not conform with current theoretical predictions that the SA1-SA2 transition should belong to the Ising universality class.