Inverted reentrant-nematic—smectic-A—smectic-Cmulticritical point

We describe a very new topology for a nematic—smectic-$A$—smectic-$C$ polycritical point which results from the insertion of a reentrant-nematic phase in an isobaric binary phase diagram. For the first time the nematic—to—smectic-$C$ transitions around this point are seen as a line of second order. Thus the $N_{\mathrm{re}}\mathrm{AC}$ point is basically different from the other $\mathrm{NAC}$ multicritical points reported so far, in the sense that the three coexisting branches are of second-order type. A short phenomenological interpretation with the use of a mean-field approach is given which agrees fairly well with the experimental results.