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

Abstract

Latent heat measurements, determined by high resolution and slow temperature scanning calorimetry (10^−3o C/min), in three compounds of differing purity—where any enantiomer of opposite handedness to that of the predominant enantiomer is included in the impurity count—suggest a correlation between blue phase stability and material purity when chiral excess is included in estimates of impurity, the data suggest that materials with less than ∼ 1.3 per cent impurities present will not exhibit blue phases even though their pitch is small enough to support blue phases. One class of compounds is discussed where this condition may indeed apply. Furthermore, the magnitude of the total latent heat of 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.