Nematic–smectic-Cheat capacity near the nematic–smectic-A–smectic-Cpoint

An ac calorimetric technique has been used to investigate the nematic (N)--smectic-C (SmC) transition near the N-SmA-SmC multicritical point in a mixture of heptyloxypentylphenylthiolbenzoate and octyloxycyanobiphenyl (7{}S5+8OCB). The heat-capacity data are well described by a Landau model in which the first-order character is very weak. Thus there is a classical tricritical point along the SmC transition line at (or very close to) the N-SmA-SmC point. No calorimetric indications of a biaxial N' phase were observed.