Reentrant transition enthalpies of liquid crystals: The frustrated spin-gas model and experiments

Specific-heat–versus–temperature curves are calculated across the reentrant (N-$A_d$-N-$A_1$) phase diagram of liquid crystals, using the microscopic ‘‘spin-gas’’ model. The transition enthalpies are found to be much weaker on each side of the partial bilayer smectic phase ($A_d$) than at the onset of the monolayer smectic phase ($A_1$). This qualitative difference, which agrees with experimental results obtained on octyloxybenzoyloxycyanostilbene (T8), is readily explained by the dipolar frustration reentrance mechanism of our model.