Cholesteric Pitch and Blue Phases in a Chiral-Racemic Mixture

Abstract

The cholesteric and “blue” phases (BP) of a mixture of the chiral and racemic forms of the same compound were studied as a function of composition and temperature. It was found that the clearing point and the cholesteric-S_A transition temperature was independent of composition. The pitch of the cholesteric at a given temperature was inversely proportional to the fraction of chiral material, as was the lattice parameter of BPII. The lattice parameter of BPI did not follow the above rule. No second-order BPI-BPIIb transition was seen.

It is concluded that this mixture is thermodynamically ideal^(6,7) in that the intermolecular interactions between two molecules are independent of their relative chirality. Thus, this system comes close to the theorist's ideal of one in which only the chirality is varied.