Latent heat measurements of the smectic A–cholesteric transition on binary mixtures

New differential scanning calorimetry measurements of the smectic A-cholesteric latent heat of transition for binary mixtures of cholesteryl nonanoate (C 9) and cholesteryl heptanoate (C 7), cholesteryl nonanoate and cholesteryl caproate (C 6) are reported for cooling cycles. These measurements give evidence of a tricritical point at approximately the reduced temperature T SACh/T Chl ≅ 0·92 for 63·1 mol per cent C 9 in the mixture of C 6 and C 9. This tricritical point occurs at reduced temperatures and concentrations different from those already obtained for heating cycles for the same mixture.