Influence of chirality on phase transitions in ferroelectric liquid crystals

The transition temperatures between various smectic liquid crystal phases are determined as a function of the enantiomeric excess for three different chiralracemic systems (i.e. binary mixtures consisting of a chiral enantiomer and its racemate). It is shown that transitions involving a ferroelectric phase occur in the chiral compounds at higher temperatures compared to their racemates, the temperature shift being proportional to the square of the enantiometric excess. In contrast, for transitions between two non-ferroelectric phases no difference between the chiral and the racemic compounds is found. Various reasons for the experimental behaviour are discussed. A chirality dependence of the transition temperature is also observed for the smectic A-isotropic transition.