Heat capacity peaks observed at the blue phase transitions in compounds of different purities.

Measurements in three compounds of differing purity show that for the latent heats of blue phase transitions determined by high resolution and slow temperature scanning calorimetry (10 sup (-3 C/min) there is a correlation between blue phase stability and material purity. The data suggest that materials with less than ~ 1.3% impurities present will not exhibit blue phases even though their pitch is small enough to do so. One class of compounds is discussed where this result may indeed apply. The magnitude of the latent heat of the blue phase transitions was observed to be sensitive to scan rates: a significantly smaller latent heat was measured at the slowest scan rates compared to faster scan rates and the magnitude of the difference was largest for the isomerically purest compound.